Ct & mr enterography

Introduction
• There was a time when small-bowel follow-through (SBFT)
was the primary method of diagnosing diseases of the
small bowel.
• Endoscopic methods for evaluating the small bowel,
including ileocolonoscopy, capsule endoscopy, and double-balloon
enteroscopy, offer distinct advantages for assessing
superficial mucosal abnormalities and obtaining biopsies
for histologic assessment. However, endoscopic evaluation
is invasive and may be limited by bowel strictures, and
techniques such as double-balloon enteroscopy and
wireless capsule endoscopy require special equipment and
expertise that are available only at large tertiary-care
centers. Moreover, no endoscopic technique allows
assessment of extraenteric abnormalities.

• In recent years, there has been renewed interest in small
bowel imaging using a variety of techniques such as
ultrasound(US), contrast enhanced ultrasound (CEUS),
computed tomography (CT), magnetic resonance imaging
(MRI), computed tomography enteroclysis/enterography
(CTEc/CTEg) and magnetic resonance
enteroclysis/enterography ( MREc/MREg) and the small
bowel endoscopic methods.
• CT and MR enterography have proven superior to
conventional barium examinations since they provide
essential information about transmural and extramural
involvements, and about the complications that may
determine surgical treatment (obstruction, fistulas,
abscesses).

Introduction
• CT enterography was first introduced by
Raptopoulos et al in 1997 as a modification to
‘‘standard’’ abdomino-pelvic CT examination to
specifically examine the small bowel in detail,
notably to assess the extent and severity of
Crohn’s disease.
• They combined neutral (low-density) oral
contrast with ‘‘enteric phase’’ CT to optimise
contrast resolution between mucosa and lumen,
thereby maximising conspicuity of abnormalities
arising from the small bowel wall.

• Several authors have subsequently described similar
techniques, which are broadly categorised into:
– CT enterography (where patients drink oral contrast) and
– CT enteroclysis (luminal contrast is introduced via a
nasojejunal tube placed fluoroscopically prior to CT
examination).
• Although superior jejunal distension is attained using
enteroclysis, the convenience, efficiency and superior
patient experience achieved with CT enterography
make it the preferred technique at many institutions.

Technique
• The technique of CT enterography combines
– small bowel distension with a neutral or low-density oral
contrast mixture and
– abdomino-pelvic CT examination during the enteric phase
following administration of intravenous contrast.
• Patients drink approximately 1.5–2 l of oral contrast over
45–60 min.
• Patient compliance is central to the success of CT
enterography, and supervision and encouragement during
the drinking phase is recommended.
• Optimising luminal distension will facilitate rapid and
efficient luminal navigation, enabling accurate detection
and characterisation of abnormalities.

Luminal contrast and distension
• Neutral or low-density oral contrast media
are a prerequisite for good-quality CT
enterography because:
– they maximise contrast between the lumen and
enhancing small bowel wall,
– facilitating assessment of mucosal thickening and
wall stratification/enhancement patterns

Oral Contrast Agents
• Water
• Water–methylcellulose solution
• polyethylene glycol,
• commercially available low-density barium,
• 0.1% Volumen (Bracco, Milan, Italy) and
• Milk
• Positive oral contrast agents

• Water
– inexpensive, well tolerated by patients, and effective for distending
the stomach, duodenum, and jejunum.
– inadequate distension due to rapid reabsorption
• polyethylene glycol (PEG) electrolyte solution
– Gastrointestinal side-effects
• Volumen; E-Z-EM, Westbury, NY
• 0.1% w/v ultra-low-dose barium with
• sorbitol, a nonabsorbable sugar alcohol
– promotes luminal distention and
– limits resorption of water across the length of the small bowel.
– The attenuation of low-concentration barium is only 20 HU.
– Fewer side effects than are associated with PEG.
– Unpleasant taste & loose bowel movements or diarrhea very soon
after the scan
• Milk
– similar results as Volumen,
– less expensive
– freely available in Europe,
– it may be deemed unpalatable by many patients when drunk in large
volumes.

• Positive oral contrast agents (containing iodine or barium)
– not routinely used for CT enterography
– they obscure mucosal enhancement, intraluminal haemorrhage
and assessment of subtle mural disease.
– problematic in creating three-dimensional images if CT
angiography is concurrently being performed—for example, in
the assessment of gastrointestinal blood loss.
• may be preferred for some clinical situations
– establish fistula patency
– exact site of mechanical obstruction
– known serosal disease,
– detection of some primary tumors, and
– patients with an iodine allergy.

Optimal Volume
• Maglinte stated that a volume of less than
1.5L is unlikely to be sufficient to adequately
distend the small bowel without active
inflammation, and a subcentimetre mass
could be missed; although,according to many
authors, good-quality examinations can be
achieved with smaller volumes.

• For the evaluation of the upper small intestine only,
– patients drink a total of two 450-mL bottles of the agent, with a
10-minute interval between each bottle.
– Water achieves the same results, is less expensive, and is better
tolerated by patients.
• For the evaluation of the complete small intestine,.
– Patients are given three 450-mL bottles, each of which is
consumed at about 15-minute intervals. The last 150 to 200 mL
is consumed just before the patient gets on the scanner.
• In small patients and patients with history of previous
small bowel resection
– smaller volumes of oral contrast may be sufficient, judged
mainly by patient tolerance.

Recommended protocol
• Avoid solid food for at least 6 h prior to
examination to decrease the possibility of
mischaracterising solid food residue as true
luminal pathology.
• Patients can liberally drink clear fluids to
maintain hydration prior to examination.
• Outside the scanner room, patients are then
encouraged to drink the oral contrast.

Intravenous Contrast
• In addition, intravenous contrast is an essential
component of CT enterography.
• It enables evaluation of:
– wall thickening,
– mucosal enhancement,
– the supplying and draining blood vessels, and
– the presence or absence of GI bleeding.
• 100 to 125 mL of intravenous contrast at a rate of
3 to 5 mL/sec, initiating the scan acquisition after
a 60-second delay.

• Maximal small bowel enhancement on MDCT has been reported
by Schindera et al to be 50 s after administration of intravenous
contrast or 14 s after aortic peak enhancement.
• Therefore administer contrast intravenously during this enteric
phase.
• The enteric phase is similar to the pancreatic phase; therefore, CT
enterography also optimises demonstration of most pancreatic
neoplasms.
• This is particularly relevant for clinicians, given that symptoms of
pancreatic tumour can mimic luminal disease.
• However, lack of portal venous phase imaging is rarely a problem
for patients undergoing CT enterography because subtle liver
metastases are rarely the target of imaging in this patient group.

Alternatively…
• Acquisition of both arterial and venous phase images at
30s and 60s respectively.
• The arterial phase images are critical for:
– appreciating subtle bowel wall for mucosal hyperenhacement
– engorgement of the adjacent vasa recta, all of which are
important signs of bowel inflammation.
• The venous phase images are important not only for
– evaluating the bowel, but also the
– other parenchymal organs of the abdomen (i.e., liver, spleen,
etc.),
– the extraenteric manifestations of Crohn’s disease,
– the venous mesenteric vasculature, and
– hypovascular bowel tumors.

• Images are acquired with thin collimation, with
acquisition of 0.625-0.75 mm slices, which are
then reconstructed into 3-5 mm axial slices for
routine interpretation.
• Coronal and sagittal multiplanar reconstructions
are directly created at the CT scanner following
the acquisition of the axial source images.
• At the same time, isotropic 0.5-0.75 mm images
are used for 3-D post-processing.

3-D TECHNIQUE
• two separate sets of 3-D reconstructions:
– Maximum intensity projection (MIP) imaging
• Effective for evaluation of the mesenteric vasculature
• Not only the main aortic branch vessels, but also tiny mesenteric
branches which are typically not readily visualized on the axial
source images.
• Areas of bowel hyperemia and mesenteric vascular engorgement
(i.e., “comb sign”, opacification of the vasa recta) are also easily
identified using this technique;
– Volume rendering (VR)
• most useful in displaying the entirety of the small bowel, and
illustrating the relationship of adjacent small bowel loops, subtle
areas of bowel wall thickening, abnormal mucosal enhancement,
and extra-enteric manifestations of Crohn’s disease

Certain medications may be helpful
but are optional.
• Metoclopramide (10 mg)
– given orally 75 minutes before the CT scan
– stimulates gastric emptying.
• Glucagon (1 mg) OR Buscopan (20mg)
– administered intravenously immediately prior to
scanning
– decrease small bowel peristalsis.

Precautions
• To avoid intravenous contrast-induced nephropathy,
– limit the use in frail and diabetic patients.
– consider reducing the volume of intravenous contrast,
– ensure patients are well hydrated before the examination and
– monitor renal function closely afterwards.
• A large volume of oral contrast is contraindicated
– who are fluid-restricted owing to clinical conditions such as
renal or heart failure.
• Following CT enterography examination, patients are
encouraged to remain in the radiology department for
approximately 45 min because they reasonably frequently
experience severe, albeit short-lived, diarrhoea.

Variations to the basic protocol -
Multiphase Scan
• In patients where active gastrointestinal bleeding is
suspected (and endoscopic work-up is negative) a
multiphase scan protocol can be used to identify sites
of occult gastrointestinal bleeding.
• This protocol would frequently include pre-contrast,
arterial, venous and delayed phase CT examinations of
the abdomen and pelvis.
• Rarely, this can be used in emergency situations to
identify the site of bleeding.
• However, the radiation burden is approximately three
times higher, and therefore potential radiation risks
should be balanced against patient benefit.

Indications for CT Enterography

LOW-DOSE CT TECHNIQUE
• peak incidence of Crohn’s disease is in
patients between the ages of 20-40 years;
• a sizeable percentage of cases are diagnosed
in children (15%); and
• the disease has a mild female predominance
i.e. radiation sensitive population,

Dose-reduction Techniques
• These include
– automated tube current modulation, which alters the
tube current (mAs) based on the patient’s size and
density;
– automated tube potential modulation, which alters
the scanner’s tube potential (kVp) based on the
patient’s size and density; and
– iterative reconstruction, an alternative to traditional
filtered back projection reconstruction techniques,
which allows the acquisition and reconstruction of
diagnostic quality images at far lower radiation doses

The Future
• CT enterography will continue to be incorporated
into wider clinical measures of Crohn’s disease,
particularly given the promise that objective CT
findings such as mural hyperenhancement can be
quantitated.
• Continuing technical developments in CT image
reconstruction will substantially reduce the
radiation dose at CT enterography, which is
already the same or less than routine abdominal
CT.

• The use of dual-source CT systems will permit
wider use of low-energy CT scanning, which will
– increase the conspicuity of hypervascular
inflammation and
– permit further radiation dose reduction.

Low-Dose 18F-FDG PET/CT Enterography
• Low-dose 18F-FDG PET/CTE, compared with CTE,
may improve the detection and grading of active
inflammation in patients with Crohn disease.
CTE demonstrates mural thickening and mucosal enhancement in loop of ileum (arrow) involved with Crohn
disease. Corresponding 18F-FDG uptake is seen on PET. Excellent anatomic registration of PET and CTE
findings on PET/CTE

PET/CTE also may reveal clinically significant findings, such as
enterocolic fistula, not evident on PET or CTE alone.
Axial CTE image (A) demonstrates thickened loop of ileum (white arrow) in pelvis and unremarkable adjacent
loop of sigmoid colon (black arrow). No fistula was appreciated on CTE.
Corresponding 18F-FDG PET image (B) reveals increased tracer uptake in ileum (arrow) consistent with active
Crohn disease; however, anatomic detail is insufficient to suggest enterocolic fistula.
Fused PET/CTE image (C) clearly demonstrates 18F-FDG uptake (arrow) bridging ileum and sigmoid colon,
with focal uptake present in wall of sigmoid colon. PET/CTE diagnosis of enterocolic fistula was confirmed at
surgery.

Technique
• A combination of good bowel distention and
ultrafast MRI sequences is required to obtain
diagnostic small-bowel images.

Contrast Media Used
for MR Enterography
• The first MR enterography studies were
performed without oral contrast (Shoenut et
al. 1993, 1994).
• One study that compares MR enteroclysis with
MRI without oral contrast has found that the
reliability for luminal findings increases when
luminal contrast is given (Wiarda et al. 2009).

Good Contrast Agent
• Important features of a good contrast agent
are:
– high contrast resolution between the bowel wall
and the small bowel lumen and
– homogeneous signal intensity of the lumen.

Classification
• Contrast media can be classified according to
how they appear on T1- and T2-weighted images.
• Negative contrast agents give low signal intensity
on T1- and T2-weighted images (“dark lumen”),
whereas positive contrast agents produce high
signal intensity on T1- and T2-weighted images
(“bright lumen”).
• Biphasic contrast agents give high signal intensity
on one sequence and low signal intensity on the
opposite sequence.

Positive Oral Contrast Agents
• Paramagnetic substances based on gadolinium-chelate,
ferrous or manganese ions.
• An increase in signal intensity at T1-weighted
sequences (appearing as bright lumen) is caused
by the paramagnetic effect that causes a
reduction in the T1 relaxation time.
• There is no effect on T2 relaxation time in the
concentrations used in clinical practice, so on T2-
weighted images the signal intensity is also high
because of the high water content of the contrast
agent.

• Wall thickening is demonstrated well by
positive oral contrast agents.
• A limitation of positive oral contrast agents is
that the luminal high signal intensity at T1-
weighted sequences may interfere with the
enhancement of the bowel wall after the
administration of intravenous contrast.

• Gadopentate dimeglumine (Magnevist Enteral, Schering AG, Berlin,
Germany)
– 1.0 mmol/L gadolinium-DTPA with
– 15 g/L mannitol
• to reduce water reabsorption in the bowel
– Mild side effects (flatulence, diarrhea, and thin stools) occur in 11% of
patients. These are caused by the addition of the mannitol.
• Ferric ammonium citrate
– mixture of granular and crystalline powders based on iron salt with
paramagnetic effects, and has to be dissolved in water (600–1,200 mg in 600
mL).
– Some patients (15%) report minor gastrointestinal side effects
• natural substances
– milk, green tea, and blueberry juice appear bright on MR because the
contents of these substances shorten the T1 relaxation time.
– Limitation of these positive contrast agents is that their signal intensity is not
constant through the gastrointestinal tract.

Negative Oral Contrast Agents
• Superparamagnetic substances that are based
on iron
• They act by inducing local field
inhomogeneties, thus resulting in shortening
T1 and T2 relaxation time.
• The signal intensity on both T1- and T2-
weighted images is thus much lower (“dark
lumen” appearance).

• These local field inhomogenities could hypothetically
lead to an underestimation of bowel wall thickness.
• The hypointense bowel wall is visualized due to the
negative contrast in the bowel lumen and the high
signal intensity of the mesenteric fat.
• The pathologic bowel wall is hyperintense after
contrast injection and the lumen remains hypointense.
• Fat suppression is recommended to suppress the high
signal intensity of the mesenteric fat for optimal
contrast after intravenous contrast injection.

• Ferumoxsil (Lumirem; Laboratoires Guerbet, Paris, France) contains
– superparamagnetic particles of iron oxide coated
in a layer of silicone that prevents it from being
absorbed by the small bowel.
• Side effects include mostly minor
gastrointestinal symptoms

Biphasic Oral Contrast Agents
• now the most widely used
• have low signal intensity on T1-weighted
images and high signal intensity on T2-
weighted images.
• On T1-weighted images, the contrast between
the enhancing bowel wall and the dark lumen
is optimized.

• These agents include:
– water,
– methylcellulose,
– mannitol (2.5%),
– mannitol (2.5%) with locust bean gum (0.2%),
– sorbitol (2%),
– VoLumen (EZ-E-M, Westbury, NY), and
– polyethylene glycol (used as a cathartic agent for
colonoscopy)

• Optimal contrast agents (eg, mannitol, locust
bean gum, and polyethylene glycol) are
hyperosmolar to prevent their absorption
across the intestinal mucosa and thereby
maximize luminal distention, in
contradistinction to less effective agents such
as water and methylcellulose.

Note!!!
• It should be noted that most, if not all,
hyperosmolar oral contrast agents may cause
gastrointestinal side effects — notably,
diarrhea. This often occurs within 1 hour of
ingestion, and all patients should be warned
of this possibility before undergoing the study,
so that they may plan the timing and method
of their travel home from the hospital.

• Water has been used as a luminal contrast
agent, as it has several advantages:
– it is widely available, cheap, and safe.
• A disadvantage is that it is rapidly absorbed,
often before it reaches the terminal ileum.
• Therefore, various additives have been
proposed to diminish intestinal absorption.

• Mannitol is an osmotic agent that can be
added, but can also cause osmotic effects such
as diarrhea and cramping.
• Nonosmotic agents such as locust bean gum
(a thickening agent extracted from the seeds
of the European carob tree) can also be used
or in combination with mannitol.

• Polyethylene glycol solution (PEG), often used as a bowel
cleansing agent, is a poorly absorbed carbohydrate that
retains fluid in the bowel lumen.
• PEG binds water molecules preventing their rapid absorption.
• As a secondary effect, it promotes peristalsis and leads to the
evacuation of bowel contents several hours after ingestion.
• Good distension has been achieved with the administration of
600mL; increasing the dosage did not improve distension.
• Similar to mannitol, PEG can cause side effects such as
cramping and diarrhea.
• PEG is less appreciated by patients because of its salty taste.

• Barium sulfate, often used in conventional
fluoroscopic exams, can be used as biphasic
contrast agent.
• The signal intensity depends on the
concentration.
• The advantage of barium sulfate is the high safety
and low cost. It is also widely available.
• The taste is a drawback for the use of barium
sulfate. Gastrointestinal side effects have been
reported

Enteric contrast agents
for MR imaging.

Technique
• A specific protocol for MR enterography requires
that the patient fast for 6 hours before the
procedure.
– decreases the amount of food residue and debris in
the intestinal lumen that can be mistaken for mass
lesions or polyps.
• Unless contraindicated, patients also follow a
low-residue diet for the preceding 5 days.
– promotes reduction of fecal matter in the colon,
which facilitates transit of the small-bowel contrast
agent because fecal material can delay transit times in
the small bowel.

• It is advised to aim for a total of 1.5 L, some
patients cannot tolerate this volume, and
adequate results may still be achieved with as
little as 500 mL.
• An oral suspension that contains 20 mg of
metoclopramide is given with the first aliquot to
promote gastric emptying.
• Just before imaging, patients are asked to drink
another 200 mL of contrast material to opacify
the stomach and duodenum.

Precaution!!!
• Colonoscopy with electrocoagulation should
not be performed directly after an MR
enterography with a mannitol solution. This as
methane and hydrogen are formed when
mannitol dissociates.

Rectal contrast administration
• Some authors have advocated concomitant
administration of a warm rectal enema to
improve the depiction of the entire colon and the
distension of the terminal ileum.
• However it is not routinely performed, but when
required, 1-1.5 l of warm saline can be
administered via the rectum, depending on the
patient tolerance.
• Antegrade colonic filling is also possible and well
tolerated, although it does not provide an
optimal colonic distension.

An Alternative!!!
• Two-step techniques have also been
described in which the patients drink:
– 2 l of PEG solution 2-4 h before the examination,
and then
– 1.2-2 l of solution, 45 min before the examination.

Imaging Timing
• Although rapid transit to the right colon (<20
minutes) in seen in some patients, most patients
require a delay of at least 40–60 minutes from
contrast material ingestion to imaging
• Some advocate imaging patients twice (eg, after
20 minutes to best visualize the distended
jejunum and then at 45 minutes for evaluation of
the ileum),

Intravenous Contrast Agents
• Detection of active inflammation can be
improved by the administration of intravenous
contrast, especially in patients with CD.
• A study with dynamic MRI has shown that the
mean peak enhancement in patients with active
CD is after 39 s (±19 s) (Florie et al. 2006).
• Administer Gadolinium (0.1 mL/kg) and start with
the postcontrast series after 60 s.
• In patients with renal impairment (low
glomerular filtration rate) or pregnancy, the
usage of intravenous contrast is contraindicated.

Anti-Spasmolytic Agents
• To prevent blurring or artifacts due to peristalsis
• N-butyl scopolamine bromide (Buscopan,
Boehringer, Ingelheim, Germany)
– Not approved for this use by the FDA
– lower costs
• Glucagon
– aperistalsis has been reported to be significantly
longer
• intravenously just before the contrast-enhanced
sequence

Technique
• 1.5-T imagers
• Large-gradient body coils are necessary for adequate
resolution and a sufficiently large field of view.
• fast imaging techniques
• Performed in breath-holds (usually between 15 and
25s)
• For breath-holds over 15 s, hyperventilation directly
prior to the sequence is advised.
• Good explanation of the procedure and length of the
breathhold is mandatory.

Patient position
• Prone imaging
– compression of the bowel loops resulting in better loop separation and can
give some reduced scan coverage due to a smaller bowel cavity in the coronal
plane, which in turn reduces the length of breath hold required, resulting in
improved patient compliance.
– It has also been shown to improve small bowel distention.
• Supine position
– more comfortable, especially in older individuals.
– normally required in patients with stomas and abdominal wall fistulas, or in
those who cannot lie prone.
• In a study that investigated this subject, prone scanning
position did lead to improved small bowel distension but not
to improved lesion detection (Cronin et al. 2008).

Imaging Protocol
• An initial thick-slab (50 mm) T2-
weighted MR
cholangiopancreatographic
sequence (HASTE) helps to
determine whether the oral
contrast agent has reached the
ileocecal junction.
• Once the contrast material
reaches the ileocecal junction, an
IV injection of 1 mg of glucagon is
administered to minimize bowel
peristalsis.
• If bowel obstruction is observed
on thick slab HASTE images, MR
fluoroscopy of the affected
segment may be performed to
assess for inflammatory
adhesions or strictures before
injection of antiperistaltic drugs.

Half-Fourier Single Shot RARE (HASTE)
• Performed in the axial and coronal plane
images with a strong T2-weighting short
acquisition times (less than 1 s per slice),
breathing artifacts are minimal.
• Normal bowel wall has low signal intensity
on HASTE sequences, an increased signal
intensity can be seen in edematous lesions
(inflammation).
• sensitive to intraluminal flow-void
artifacts.
– because of peristaltic motion,
– limited by spasmolytic drugs
• used for measuring wall thickness,
– because it is not sensitive to the chemical shift
artifact.
• performed using fat suppression.
– To differentiate between Fat and edema
(intramural edema of the bowel wall is indicative
of inflammation)

Balanced Steady-State Free
Precession (True-FISP)
• (true Fast Imaging with Steady-state
Precession; True-FISP)
• More complex in generation of tissue
contrast.
• This tissue contrast comes from both T1
and T2 in a ratio, namely the T2/T1 ratio.
• A higher ratio corresponds with higher
signal intensity.
• At 1.5 T, the bowel wall has an
intermediate to low signal intensity and
fluids have a high signal intensity.
• provide high contrast between the bowel
wall, lumen, and mesentery.
• Flow-void (motion) artifacts are not so
common
• The most common artifact in the true-FISP
sequence is the black boundary artifact,
due to chemical shift.
– however, fat suppression helps in reducing
the effects of this artifact

Balanced Steady-State Free
Precession (True-FISP)
Black boundary artifact Not seen with fat saturation

T1-Weighted Sequences
• Contrast-enhanced T1-weighted gradient echo
sequences with fat suppression
– to assess whether there are areas of increased
enhancement
• either two-dimensional (2D) or three-dimensional
(3D).
• Commonly used is the 3D T1w interpolated volume
imaging sequence (3D VIBE: Volumetric Interpolated
Breath-Hold Examination or comparable sequences)
• To reduce the acquisition time, small flip angles and
short TR (repetition time) are used.
• recommend a precontrast coronal series and coronal
and axial postcontrast series to optimal assess the
bowel wall enhancement.
• 3D ultrafast gradient echo sequences are sensitive to
bowel peristalsis, so spasmolytic drugs are advised.
– an additional 10 mg of hyoscine butylbromide or 0.2 mg of
glucagon prior to gadolinium-based contrast material
injection (0.2 mg/kg).

Coronal True FISP image:
normal bowel. The ‘black
boundary’ artefact may be
confused with bowel wall
thickening (arrows)
Coronal T1 fat-saturated post-contrast
image: normal bowel
wall shows mild homogeneous
enhancement
Coronal fat-saturated HASTE
image: normal bowel.
Intraluminal flow voids
(arrow) are seen, as this
sequence is sensitive to fluid
motion

• The imaging plane in these sequences is
– aligned parallel to the bowel segments
• to allow detailed visualization of mucosal irregularities
and
– aligned perpendicular to the bowel
• to provide accurate visualization of transmural ulcers,
fistulas, sinus tracts, and periintestinal abnormalities.
• The total in room time of the examination is
approximately 30 - 45 min.

Pitfalls
• suboptimal distention of bowel loops can be
encountered more commonly.
– Early mural changes of Crohn disease may be
overlooked in areas of collapsed bowel segments.
– Partial strictures may also not be identified because of
inadequate distention of the bowel.
• Artifacts due to peristalsis or flow voids are more
prominent on HASTE sequences.
– Intraluminal food debris may simulate filling defects
or polyps; a low-residue diet and fasting before
examination help in reducing these artifacts.
• Previous surgery, particularly stricturoplasty, may
mimic tumors with a shouldered margin or
fibrotic strictures.
– Observation of these segments in all three planes
helps in distinguishing stricturoplasties from tumors
because stricturoplasties typically have a lobulated or
bi- or trifoliate appearance. Coronal HASTE image with fat
saturation (4-mm thickness) shows
linear filling defect in bowel lumen
(arrow) due to peristalsis

Diffusion-Weighted Imaging (DWI)
• DWI at MR enterography has been
researched recently in one small study
of 11 patients for detection of active
CD (Oto et al. 2009).
• In patients with active CD, ADC values
are decreased, indicating diffusion
restriction.
• The sensitivity for detecting
inflammation with DWI was 95% and
specificity 82%.
• More studies have to be performed to
test the reproducibility of these data
and the relevance in comparison with
other MR findings.
• Hence it is suggested that DWI may
have a role in imaging of patients for:
– whom IV contrast administration is
contraindicated or
– who cannot tolerate oral
preparation.

Cine Imaging / MR fluoroscopy
• to obtain information about peristalsis and bowel
motion.
• allow both qualitative and quantitative
assessment of bowel motility.
• The most common indication is the diagnosis of
adhesions, which are visualized by fixation of
bowel loops and lack of normal peristalsis.
• This is best seen on true-FISP images
• a frame rate of 0.5–2 sections per second along
the long axis of the affected segments.

Magnetization Transfer Imaging
• role in imaging of fibrosis in Crohn disease
• Magnetization transfer imaging reflects the transfer of
energy from protons in free water molecules to those
associated with large molecules such as collagen.
• Fibrotic tissues therefore have a high magnetization
transfer effect.
• An in vivo study of nine patients with ileal Crohn
disease showed the magnetization transfer ratio was
highest in patients with a stricturing disease
phenotype, supporting the use of MRI to image enteric
fibrosis

Future Prospects of MR Enterography
• Research now is focused on:
– creating abdominal 3 T protocols,
– studying perfusion and diffusion and
– obtaining more insight into the role of MRI in determining disease
activity in CD.
• New techniques are being developed to assess bowel wall
enhancement in a more objective manner. With the creation of so-called
T1-maps, the absolute T1-value can be calculated and
therefore the absolute contrast enhancement.
• Recently, more research is being performed on dynamic contrast-enhanced
MRI (DCE-MRI) in CD. Mural hemodynamic parameters
derived from DCEMRI were reported to be correlated with disease
chronicity and microvessel density was inversely related to mural
blood flow (Taylor et al. 2009).

ENTEROGRAPHY INTERPRETATION:
HOW TO REVIEW AND AVOID PITFALLS

Reading Technique
• Careful luminal navigation from the gastro-oesophageal
junction to the anus, or vice versa.
• Can take several minutes (up to 15 min in some
patients) and can be thwarted by poor luminal
distension or collapse, particularly when there is
minimal intra-abdominal fat separating loops.
• Use of a multiplanar review will improve accuracy
of both luminal navigation and interpretation

• first distinguish abnormal from normal
segments.
– differential contrast enhancement is a cardinal
sign of many small bowel pathologies.
– hyperenhancing mass
– focus of wall thickening.

• The jejunum occasionally
is collapsed at
enterography, which can
be a normal finding in the
minority of cases, but the
ileum almost always is
distended adequately.
• the enteric phase of
enhancement the
jejunum enhances more
than the ileum.
• This should not be
mistaken for pathology.
Normal CT enterography. Coronal CT
enterography image showing normal jejunal
(short arrows) and ileal (long arrrows) loops.
Note the prominent mucosal pattern in
the proximal jejunal loops.

• Furthermore, collapsed bowel
loops appear to enhance more
than the distended loops in
the same segment.
• In the non-distended loops,
other signs of disease must be
used to diagnose pathological
processes, including
associated changes in the
adjacent small bowel
mesentery such as
hypervascularity, fat stranding
or lymphadenopathy.
Collapsed small bowel. Axial CT enterography
image showing a collapsed small bowel
mimicking pathology (long arrow) compared
with a normal fluid-filled loop (short arrow).
Note the absence of any associated changes.

• Focal small bowel spasm is
frequently encountered,
despite the use of Buscopan,
and can mimic short
strictures.
• Identification of similar
areas of spasm, lack of
mucosal hyperenhancement
and absence of mesenteric
abnormality helps to
distinguish spasm from true
pathology
Small bowel spasm. Axial CT enterography
image showing two areas of focal small bowel
spasm mimicking pathology (arrows). Note the
absence of any associated changes.

• Repeat scanning through the section of
interest is often useful to distinguish stricture
from a collapsed loop, but clearly the dose of
ionising radiation imparted by CT makes this
less applicable than during MRI enterography.
• As noted above, multiplanar reformatting
when reporting CT enterography has been
shown to increase diagnostic confidence and
sensitivity.

Characterisation of small bowel
pathology
• Interpretation of small bowel abnormalities
can be divided into:
– Luminal (Wall, Fold and Mucosal) changes
– Extra Enteric changes
– Colonic abnormalities

Intestinal ulcers
• An aphthous ulcer may be seen
on high-resolution MR images as
a nidus of high signal surrounded
by a rim of moderate signal
intensity.
• The presence of aphthous ulcers
provides strong evidence for
Crohn disease in the appropriate
clinical setting.
• Aphthous ulcers are also seen in
other conditions such as
infections, tuberculosis, and
ischemic enteritis, but aphthous
ulcers are encountered less
commonly in these entities than
in Crohn disease.
Axial FIESTA images show mural thickening of
the terminal ileum with submucosal edema
and irregular mucosal surface with some focal
ulcerations (white arrows).

• Advanced inflammation in
Crohn disease manifests as
deep ulcerations and a
cobblestone mucosal
appearance.
• Deep transmural ulcers
manifest as linear, high-signal-intensity
protrusions into the
bowel wall on fast imaging
with steady-state precession
(FISP) and HASTE sequences.
• True FISP images have a black
boundary artifact that may
mask smaller transmural
ulcers. Coronal true fast imaging with steady-state
precession image obtained with fat saturation
shows thickened, inflamed segments of ileum
with deep ulcers seen as high-contrast
protrusions within bowel wall (arrow).

• Axial HASTE image
shows good bowel
distention, a short
terminal ileal stricture,
wall thickening, and a
deep rose thorn ulcer
(arrow), findings that
are infrequently seen at
enterography

• Early and superficial ulceration is not well
demonstrated even with full luminal distention at
MR imaging or CT, and well-performed conventional
fluoroscopy still holds an advantage
MR enterogram shows no
ulceration in an asymmetrically
thickened terminal ileal
segment (arrowhead) lying
adjacent to the transverse
colon (arrow).
Image from a small bowel
follow-through study clearly
shows ulceration in the
terminal ileal segment..

Wall thickening
• Although this feature is not
entirely specific for Crohn
disease, any thickening of the
small bowel wall greater than 3
mm should be considered
abnormal.
• In patients with small bowel
Crohn disease, wall thickness
usually ranges between 5 and 10
mm.
• The black border artifact seen on
true FISP images can complicate
the assessment of bowel wall
thickness. Bowel wall thickness is
more accurately assessed with a
HASTE sequence

Fold Pattern
• Three main alterations in fold pattern are
recognized:
– the picket fence pattern of diffusely thickened
folds,
– a reduction in or distortion of folds due to
ulceration, and
– cobblestoning.

(a) picket fence pattern of diffusely
thickened folds,
• 47-year-old man with
proven Crohn disease.
• Coronal HASTE image
shows nodular (arrow),
thickened, and
asymmetric folds in
distal ileum
(arrowhead).

(a) picket fence pattern of diffusely
thickened folds,
Small bowel Crohn disease in a 66-year-old man who had
previously undergone right hemicolectomy and presented with
recurrent symptoms. Axial (a) and coronal (b) HASTE images show
a small volume of free fluid between small bowel mesenteries
(arrows), but no loculation, encapsulation, or mass effect as would
be expected with an abscess. There is a “picket fence” pattern of
fold thickening in the neoterminal ileum, along with wall
thickening (arrowheads).

(b) reduction in or distortion of folds due to ulceration
Distortion or blunting of the mucosal folds and thickening of the valvulae conniventes.
(A) Coronal SSFSE image shows thickening and blunting of valvulae conniventes of the terminal
ileum with a pseudopolypoid appearance (white arrows in (A).
(B) Endoscopic view shows mucosal ulcers and edema (black arrows) in the terminal ileum.

(c) Cobblestoning
• It manifests as sharply demarcated patchy areas of
both high and moderate signal intensity within an
affected bowel wall segment caused by longitudinal
and transverse ulceration, producing a cobblestone
pattern.
• This finding is best appreciated on true FISP images,
which are less sensitive to intraluminal flow void.
• Although cobblestoning is best seen in well-distended
bowel at MR enteroclysis, it can also be identified on
good-quality MR enterograms.
• The mesenteric border is preferentially affected in
Crohn disease

Stricture
• defined as functionally significant if there is upstream bowel
dilatation greater than 3 cm, or
• as nonfunctional if there is a greater than 10% narrowing in the
bowel lumen compared with normal adjacent bowel in the absence
of dilatation.
• In Crohn disease, strictures are invariably associated with a
segment of thick-walled bowel, whereas adhesive strictures do not
demonstrate this finding.
• However, in isolation, a stricture with wall thickening does imply an
extensive differential diagnosis, which includes infections, radiation
enteritis, or neutropenic enteritis in immunocompromised patients
(in the latter two conditions, an appropriate antecedent history
would be expected) and malignancies such as carcinoid tumors and
lymphoma.

Acute Wall Edema
• Higher than normal wall T2 signal intensity, best seen as
longitudinal intermediate signal intensity (within what is
normally hypointense bowel wall) affecting the thickened
bowel wall on fat-saturated HASTE images, may be related to
mucosal or submucosal edema and has been shown to
correlate with independent indexes of Crohn disease activity.
• Axial HASTE image
shows higher than
normal wall signal
intensity (arrowhead).
• Axial fat-saturated
HASTE image shows
apparent wall edema
from active
inflammation in the
defunctioned segment
(arrowhead)

• In a histology matched study, the mural signal
intensity on T2-weighted images was compared
with cerebro-spinal fluid (CSF) signal intensity.
• The ratio of these signal intensities (T2 mural/CSF)
was positively correlated with histology (a higher
ratio denotes a more inflamed bowel wall)(Punwani et
al. 2009).

• This may allow differentiation from fibrotic
wall thickening, which usually has low to
moderate T2 signal intensity on true FISP and
HASTE images.
• However, the absence of wall hyperintensity
does not exclude active disease, whereas the
presence of high signal intensity can result
from intramural fat deposition, found in
chronic strictures.

Chronicity and Wall Fat
• Fatty infiltration of the
bowel wall may occur in
chronic IBD, and both the
small bowel and colon may
be affected.
• Notably, however,
intramural fat deposition is
a nonspecific finding that
can be seen not only in
other causes of chronic
bowel inflammation, but
also in the setting of
obesity, steroid use, and
diabetes.

• Generally, fat-saturated and non-fat-saturated T2-weighted
HASTE sequences are required to differentiate fat from wall
edema, with the latter demonstrating persistent high signal
intensity with both sequences, whereas fat saturation will
reduce wall signal intensity that is due to fat.
• Gradient-echo (FISP) sequences demonstrate chemical shift
artifact in the presence of intramural fat.
Intramural fat in a patient with chronic ileal Crohn disease. (a) HASTE image shows focal midileal
wall thickening with associated linear intramural high signal intensity (arrow). (b) Gradient-echo
FISP image shows chemical shift artifact as a thin black stripe in the corresponding location
(arrow), a finding that confirms the presence of intramural fat rather than edema.

Patterns of Wall Enhancement
• Mural enhancement is best assessed by
comparing
(a) abnormal bowel with adjacent normal
loops, or
(b) bowel loops that are at a similar
distance from the center of the field of view to
mitigate for field inhomogeneity, which may
otherwise influence the apparent level of
enhancement

Enhancement pattern
• Small bowel wall enhancement patterns have
been divided into:
1. ‘‘target’’ appearance,
2. homogeneous mild
3. homogenous hyperenhancement
4. heterogeneous and
5. diminished.

1. Target/stratified/layered
appearance with
stratification of the layers
of the small bowel wall
(mural stratification) is
generally found with
benign conditions — for
example, vasculitis,
Crohn’s disease, venous
thrombosis with
associated bowel oedema
or ischaemia and
intramural haemorrhage.
Coronal VIBE image shows stratified
contrast enhancement, with avid
enhancement of the mucosa
(arrowheads) relative to the submucosa
and muscular layers (arrows), findings
that help confirm active Crohn disease.

Different types of mural stratification
Soft tissue density mural
thickening of the terminal
ileum representing
inflammatory infiltrate in a 34-
year-old male with newly
diagnosed active Crohn’s
disease.
Fluid density mural
thickening of the distal
ileum representing
submucosal oedema in a
62-year-old female with
recurrent Crohn’s disease.
Fat density mural
thickening of the terminal
ileum in a 62-year-old
female, representing
chronic active inflammation

2. If wall enhancement is
homogeneous and mild
(i.e. similar to muscle),
chronic inflammatory
conditions should be
considered, particularly
those producing fibrosis
within the small bowel
wall (for example
Crohn’s disease,
ischaemia and radiation)
Coronal contrast-enhanced T1-weighted fatsuppressed
image of a patient with no history of surgery, but with
similar symptoms, show thickening and stenosis of the
terminal ileum with homogeneous contrast enhancement
(arrows), compatible with chronic stenosis.

3. Homogeneous
hyperenhancement
represents transmural
inflammation is commonly
seen with active Crohn’s
disease, and is frequently
associated with increased
density in the surrounding
mesenteric fat.
• Indeed, it has been
roposed by Bodily et al that
a cut off of 109HU can be
used with reasonable
accuracy
Gadolinium-enhanced image shows diffuse
hyperenhancement relative to normal adjacent
bowel (arrowheads), a finding that further
confirms active disease.

4. Heterogeneous enhancement is seen in
small bowel neoplasms, including
gastrointestinal stromal tumours,
adenocarcinomas, metastases and peritoneal
deposits.
5. Decreased enhancement is typical of bowel
ischaemia, and usually precedes the
development of intramural gas and
subsequent perforation.

• In addition, the absolute level of bowel wall
enhancement has been suggested as a marker
for disease activity.
• The peak signal intensity of mucosal
enhancement has been shown to have good
correlation with the Crohn disease activity
index.

Active Crohn disease.
Dynamic axial contrast-enhanced three-dimensional gradient-echo MR images (left to right, top
to bottom) show progressive rapid bowel wall enhancement within the first 70 seconds after
injection of contrast material.

Length of small bowel involvement
• For the purpose of differential diagnosis, the length of small bowel
involvement can be divided into three:
– focal (5 cm)
• neoplasms, endometriosis, small bowel diverticulitis, foreign body
perforations, small bowel ulcers (secondary to non-steroidal anti-inflammatory
drugs) and occasionally granulomatous processes like tuberculosis and Crohn’s
disease
– segmental (6–40 cm)
• intramural haemorrhage, Crohn’s disease, lymphoma, infectious enteritis and
ischaemia, particularly due to superior mesenteric artery (SMA) embolus or
superior mesenteric vein (SMV) thrombosis.
• In a patient with previous malignancy and segmental involvement, previous
radiotherapy should be considered
– diffuse (40 cm)
• hypoalbuminaemia, low-flow intestinal ischaemia, vasculitis, graft vs host
disease and infectious enteritis

Location of pathology within the small
bowel wall
• The mucosa is seen to be predominantly affected
in inflammatory conditions like Crohn’s disease,
tuberculosis and neoplasms such as
adenocarcinoma.
• The predominant abnormality is seen in the
submucosa in conditions like intramural
haemorrhage, vasculitis, ischaemia,
hypoalbuminaemia and angio-oedema.
• The serosa is predominantly involved in
metastases, endometriosis, carcinoid and other
inflammatory conditions in the peritoneum.

Pseudosacculation-Pseudodiverticulum Formation
• Pseudosacculations are a consequence of relative sparing
of the antimesenteric border within an affected bowel
segment.
• Fibrosis and shortening of the diseased mesenteric wall
lead to apparent dilatation of the opposing normal bowel
wall.
• Because all three bowel wall layers form the sacculation (in
contrast to colonic diverticular disease), such a finding may
also be referred to as a pseudodiverticulum .
• Abnormal bowel segments frequently demonstrate other
features of chronic Crohn disease, such as fibrofatty
infiltration of the wall, wall thickening, and fat wrapping.

Multiple pseudodiverticula in a 33-year-old woman. US demonstrated thickened right iliac fossa bowel loops.
(a) Coronal HASTE image shows pseudosacculation produced by asymmetric thickening of the terminal ileal
mesenteric border.
(b) Coronal fat-saturated HASTE image shows intermediate-signal-intensity mesenteric edema (arrows)
tracking from the bowel segment shown in a, a finding that is appreciated only with fat saturation.
(c) Gadolinium-enhanced image shows diffuse hyperenhancement relative to normal adjacent bowel
(arrowheads), a finding that further confirms active disease.

Extra-enteric Assessment
• One of the major advantages of CT and other
cross- sectional techniques is their ability to
visualise the extraluminal soft tissues.
• It is therefore important to carefully evaluate
the structures beyond the bowel wall.

Mesenteric Blood Vessels
• Patency or otherwise of mesenteric blood
vessels should be assessed to exclude a
vascular pathology such as arterial embolus or
venous thrombosis.

Comb Sign
• corresponds to increased mesenteric vascularity.
• identified as short low-signal-intensity parallel
lines on true FISP images, oriented perpendicular
to the longitudinal axis of the affected bowel
wall.
• On contrast material–enhanced VIBE images, the
comb sign is seen as high-signal-intensity parallel
lines due to contrast enhancement of the
vasculature.
• The presence of the comb sign may suggest
active disease.

Mesenteric Edema
• Mesenteric edema is present
in some (but not all) patients
with advanced active disease,
and it tracks along the
adjacent mesentery from an
inflamed bowel loop.
• Seen particularly on fat-suppressed
sequences.
• There is typically
accompanying bowel wall
edema and
hyperenhancement, findings
that are commensurate with
active disease.
Coronal fat-saturated HASTE image shows intermediate-signal-intensity mesenteric
edema (arrows), a finding that is appreciated only with fat saturation.

Fat Wrapping
• Increased mesenteric fat producing a
mass effect and manifests as
anatomic displacement of mesenteric
vessels or surrounding abdominal
viscera.
• Frequently asymmetric, preferentially
involving the mesenteric border of the
bowel, although there is often
fibrofatty proliferation encircling
involved bowel loops.
• Fat wrapping usually occurs in
patients with long-standing,
established transmural inflammation,
and it is a very specific sign for Crohn
disease (its presence may help in
narrowing the differential diagnosis
for small bowel disease).
Sequela of chronic Crohn’s related bowel
inflammation. Twenty-seven year-old male
with Crohn’s disease. Axial images
demonstrate diffuse fat deposition
in the wall of the rectosigmoid colon (A, B), as
well as marked fibrofatty proliferation
(“creeping fat”) (B) surrounding the rectum.

Lymph Nodes
• Better on T2-weighted FISP images.
• Small-volume lymph nodes can be seen adjacent
to normal bowel segments and to those affected
by active and inactive Crohn disease.
• However, hyperenhancement, enlargement, and
edema of lymph nodes seen with fat-saturated
VIBE & FISP sequences are highly suggestive of
active Crohn disease in patients in whom this
diagnosis has been established.

• FISP image shows a distended terminal ileum (arrow) but no focal thickening. Arrowheads
indicate lymph nodes.
• HASTE image clearly delineates a thickened terminal ileum (arrow) but not lymph nodes.
• VIBE image shows abnormal enhancement of the ileal wall (arrow) and lymph nodes
(arrowheads).

Mesenteric lymphadenopathy in a patient with Crohn disease. Coronal HASTE (a) and
balanced SSFP (b) MR images show mesenteric adenopathy (arrowheads), which is
much more conspicuous in b

• Nodes typically lie along the vascular supply of
an affected disease segment (eg, ileocolic
vessels in terminal ileal disease) but may be
spatially remote from the segment.
• Enhancement, when present, is usually
homogeneous.

• Nonenhancing nodes in
the presence of
adjacent bowel wall
thickening and nodal
edema may indicate an
alternative diagnosis to
Crohn disease.
• Necrotic caseating
nodes are present in
tuberculosis and, more
rarely, in histoplasmosis MR image shows central nonenhancement (arrows),
a finding that suggests necrosis (confirmed at CT),
and a pattern of nodal change (arrowheads) that is
atypical for Crohn disease. Results of laparoscopic
lymph node biopsy confirmed histoplasmosis

Fistulas and Sinuses
• Up to 1/3 of Crohn’s patients
develop a fistula within the first
ten years after exhibiting
symptoms of Crohn’s disease.
• While the perianal region is the
most common site of fistula
formation, fistulas can develop
anywhere in the abdomen,
including enteroenteric,
coloenteric, colocolic,
rectovaginal, enterocutaneous,
and enterovesicular fistulas.
• Deep transmural ulcers may
ultimately communicate with
an adjacent epithelial surface
and so become fistulas.

• In the most obvious cases,
an enhancing tract can be
traced, clearly identifying
the presence of a fistula.
• Fistulas that are visible at
MR enterography typically
manifest as high-signal-intensity
tracts on T2-
weighted images and
enhance avidly following
gadolinium-based contrast
material administration.

• Coronal HASTE image again shows the ileum (arrow) in
proximity to the sigmoid colon (arrowhead).
• Coronal fat-saturated HASTE image shows a high-signal-intensity
tract (straight arrow) connecting the ileum (curved arrow) and
the colon (arrowhead).

• 32-year-old man in
treatment for known
Crohn disease.
• Coronal true fast imaging
with steadystate
precession image
obtained with fat
saturation shows ileoileal
fistula (arrow).
• Note that fistula does not
contain any fluid or air
within patent lumen but
appears isointense.

• A sinus is defined as a blind-ending tract that
arises from bowel but does not reach another
epithelium-lined surface.
• Sinuses also manifest as high-signal-intensity
tracts on T2-weighted images and appear
similar to fistulas, sometimes in association
with abscesses.

Enterocutaneous Fistulas
• Imaging with the patient supine is
recommended to mitigate against the field
inhomogenity if such fistulas are suspected
clinically.
• Conventional techniques such as fistulography
may still have an important problem-solving
role in difficult cases involving the abdominal
wall.

37-year-old woman with known Crohn disease and previous ileorectal anastomosis.
A, Axial true fast imaging with steady-state precession image shows large enterocutaneous
fistula (arrow) containing high-signal enteral contrast material and surrounding inflammation.
B, Intraoperative photograph shows fistula opening in bowel wall (arrow) and marked mural
thickening (arrowhead)

• However, in many cases a
discrete tract will not be
identified, and the presence of
a fistula must be surmised by
secondary signs.
• In particular, the presence of
ectopic gas in the midst of
bowel loops, tethering and
spiculation of adjacent bowel
loops, and soft tissue
stranding and density in the
midst of tethered bowel loops
can be seen in the presence
“complex fistulizing” Crohn’s
disease.

• Incipient or early fistulas
manifest as linear areas of
moderate signal intensity
arising from the bowel wall.
• These fistulas may be
difficult to visualize because
of partial volume averaging
and the lower spatial
resolution of MRI.
• Multiplanar imaging of the
bowel is useful for a
complete assessment and
avoidance of missed
sinuses.
Coronal true FISP image obtained with fat
saturation shows active inflammation in distal
ileum. Small linear projections (arrows) are
seen arising from bowel; these findings are
indicative of incipient fistulas or sinuses.

• Ectopic gas in other
locations, including the
bladder and
subcutaneous soft
tissues, should also raise
concern for a fistula, and
should not automatically
be assumed to be
secondary to a foley
catheter or soft tissue
injections.
Coronal CT enterograms reveal that the
irregularly shaped fistula (arrowheads) courses
anterior to a bowel loop (arrows) and extends
to the urinary bladder.
Air is seen within the bladder, a finding that is
consistent with fistula.

A 22-year-old female with Crohn’s disease and persistent pelvic pain.
An abnormally thickened loop of distal ileum is present in the pelvis (a–d, chevron).
Note the wide-mouthed fistulous connection (a–d, small arrows) with the left ovary (a–d, arrowheads), which has become
enlarged with an intra-ovarian phlegmon (c, asterisk) as a sequela of long-standing Crohn’s disease. There is also tethering
of this diseased bowel to adjacent small bowel loops in the pelvis (a–d, large arrows), but
no severe, active inflammation is identified on fatsaturated T2W images (a–d).

Small Fistulas
Enterocolic fistula in a 36-year-old woman who presented with clinical relapse after undergoing
right hemicolectomy for Crohn disease.
(a) Coronal HASTE image shows a thickened ileum (arrowhead) a few centimeters from an
ileocolic anastomosis. Arrows indicate the path of the transverse colon.
(b) Image from a subsequent small bowel follow-through study shows a fistula (arrow) from the
ileum to the transverse colon. In hindsight, the fistula was visible at MR enterography.
Fistulization can be difficult to appreciate, and dynamic imaging with compression (eg, a
small bowel follow-through study) has advantages in some doubtful cases.

Abscess
• An abscess is a well-defined,
encapsulated
collection of pus.
• Abscesses do not conform
to normal peritoneal
reflections (unlike free
fluid) but do have the
signal intensity
characteristics of fluid (ie,
high signal intensity on
T2-weighted images, low
signal intensity on T1-
weighted images), and
their rim often enhances
strongly.
Abscess in a 29-year-old man with known Crohn
disease who presented with clinical relapse.
Coronal gadolinium-enhanced VIBE image
shows a high-signal-intensity fluid collection 2
cm in diameter with intense wall enhancement
(arrowheads), a finding that is consistent with
an abscess. The abscess responded to
intravenous antibiotic therapy.

• MR enterography is very
sensitive for the detection
of abscesses, but unlike CT,
MR imaging may fail to help
detect small volumes of gas
within an abscess.
• The detection of any
intraabdominal abscess is
important because the use of
anti–tumor necrosis factor
agents such as infliximab is
contraindicated in the
presence of intra-abdominal
abscess.

• Reactive loculated peritoneal
fluid is occasionally seen in
patients with severe
nutritional failure, in patients
with long-segment
inflammation, or as a normal
physiologic finding in young
women with Crohn disease.
• It may mimic abscess, but it
will not demonstrate an
enhancing wall or adjacent
peritoneal thickening, and it
will have uniform high signal
intensity.
Axial HASTE images show a small volume of
free fluid between small bowel mesenteries
(arrows), but no loculation, encapsulation, or
mass effect as would be expected with an
abscess.

Colonic Abnormalities
• This technique is specifically aimed at maximizing
detection of small bowel disease and hence
colonic distention may not be optimimal.
• Lack of prior laxative bowel preparation can
sometimes interfere with the assessment of
mucosal hyperenhancement, since colonic fecal
residue can be hyperintense with T1-weighted
sequences, and underdistention or collapse may
cause difficulty in accurately measuring wall
thickness.

Crohn colitis.
• Axial three-dimensional
gradient-echo MR image
obtained with intravenous
contrast material shows
mucosal
hyperenhancement and
wall thickening in the colon
(arrows), findings consistent
with active inflammation.
• In this case, adequate
colonic visualization was
achieved because of
antegrade filling.

Decision Making!!!
Choice of Small Bowel Imaging
Technique: General Considerations

The Radiation Issue
• It is now clear that access to multidetector computed tomography
(MDCT) has led to an increase in population radiation exposure.
• The benefits of MDCT are also well known.
• However, patients with small bowel pathology, particularly those
with Crohn’s disease, frequently undergo multiple studies over the
course of their disease, especially during acute episodes or when
complications arise (Desmond et al. 2008). This can result in
significant radiation accumulation;
• Nuclear medicine studies and barium examinations carry a lower
but not insignificant radiation burden. Many individuals with small
bowel disease are young, so where possible radiation-free imaging
is preferable .
• For this reason, small bowel MRI and ultrasound examinations are
advantageous, where clinically appropriate.

Invasive Investigations: Bowel
Preparation and Tubes
• Cathartic bowel preparation is unpopular with
patients (Jensch et al. 2008), but may be an
important aspect of barium examinations of the
small bowel, WCE, and DBE.
• Purgation is not always necessary prior to CT,
nuclear medicine, or MRI studies, depending on
the indication and clinician preference, but the
bowel distension agent may be a laxative, for
example polyethylene glycol (PEG), or have a
significant laxative side-effect (e.g., mannitol)
(Lauenstein et al. 2003).

• Nasojejunal intubation without sedation for
enteroclysis is tolerated but unpopular with
both patients and most radiologists.
• Tube placement by less experienced operators
or in more difficult cases may result in higher
screening times, imparting a significant
radiation dose and thereby increasing the
radiation dose in a CTE procedure or negating
the benefit of using MRI to avoid radiation.

• While sedoanesthesia makes the procedure
more comfortable for patients, it requires
additional monitoring and staff to prevent
complications and has implications for the
patient following the procedure.
• MR enteroclysis examinations also result in
significantly more discomfort and abdominal
pain following the procedure than
enterography.

Acute vs. Elective Evaluation
• While similar out of hours access may be available for
ultrasound and CT, the same is not always true for
other modalities, particularly MRI.
• In acutely unwell patients, a MDCT scan is quicker and
needs fewer breath-holds than MRI, improving patient
compliance in what is often a difficult clinical situation.
• In severely ill patients, the length of examination and
limited access for clinical assessment during the scan
may render MRI completely inappropriate.
• Even in an elective outpatient setting, limited access of
MRI may restrict its usage.

Capacity and Hardware
• Access to high-quality body surface coils and
adequate field strength scanners (1.5 T or
higher) are essential.
• Need for balancing ever increasing MRI
service demands for other clinical indications.

Disease Stage
• Aphthous ulcers, the earliest manifestation of
Crohn’s disease, are best demonstrated
radiologically with traditional barium studies.
• Patients presenting with advanced stages
need a cross-sectional imaging.

Extra Enteric Assessment
• A clear benefit of cross-sectional imaging over
barium examinations and endoscopy

SMALL BOWEL ASSESSMENT: HEAD-TO-HEAD
COMPARISON – GENERAL CONSIDERATIONS

Radiology or Endoscopy?
• An obvious advantage of endoscopic techniques is
direct visualization of the enteric mucosa and the
ability to detect subtle lesions beyond the resolution of
radiological investigations, including telangectasias,
mucosal hyperaemia (the earliest visible sign of Crohn’s
disease), and aphthous ulcers.
• Other endoscopic possibilities include various
interventions biopsy, polypectomy, ablation of vascular
malformations, and tattooing to aid identification of
pathology for laparoscopic resection.

• Disadvantages would include:
– Often long
– Sedation or anaesthesia
– Significant learning curve
– interventional tools is more limited
– Expensive eqipments
– Limited expertise
– Risk of retension/obstruction (WCE)
– Difficult anatomical location (WCE)
– Proximal lesions may be missed due to rapid transit (WCE)
– Limited battery life (WCE)
– Information beyond the bowel - nil

• Overall, radiology and endoscopy are not
mutually exclusive but frequently
complimentary in such cases.

Enterography or Enteroclysis
• While enteroclysis is inherently invasive, usually
unpopular with patients and incurs additional
financial cost and radiation exposure, distension
is undoubtedly superior, particularly in the
jejunum.
• There is, therefore, a reasonable argument that
the superior quality of enteroclysis justifies its
invasiveness in the first diagnosis of polyposis
syndromes and CD, with enterography more
suited to follow-up of patients with established
disease.

• Enterography is, however, highly
advantageous in a paediatric population and
in other patients where nasojejunal intubation
is unsuitable or not tolerated.
• It is also less time-consuming

Advantages of MRI
• lack of ionizing radiation
• high tissue contrast resolution.
• ability to provide accurate anatomic detail;
• depict extraintestinal abnormalities; and
• facilitate distinction between phlegmon, abscesses,
and mesenteric lymphadenopathy.
• MR fluoroscopy can also be performed to assess
stricture and obstruction.
• perfusion MRI to assess for recurrent inflammation and
fibrosis
• high-resolution MRI in the detection of early ulceration

Limitations of MRE
• still somewhat limited expertise and
availability
• Longer time (30 min vs 30 sec)
• Sedation for very young children and for
patients with claustrophobia
• Absolute contraindications to MRE
(pacemaker, implants…..)

MRE v/s VCE
• Three studies concluded that both MRE and
VCE identified diseased small bowel;
• However, VCE was better at identifying small
aphthous lesions and often identified more
lesions.
• MRE is insensitive to early mild disease
restricted to the mucosa.

MRE vs SBFT/conventional enteroclysis
• full agreement in revealing, localizing, and
estimating the length of bowel involved.
• MRE (with MR-enteroclysis) was poor at
detecting superficial ulcers but performed well
in identifying deep ulcers and stenosis.

MRE vs CTE
• No radiation risks
• MRE more accurately describe the submucosal
pathology of transmural Crohn’s disease.
• ability to differentiate inflammation from fibrosis
within the submucosa of the bowel wall and in
the peri-enteric tissues.
• MRE can show extra-intestinal disease (including
bowel obstruction, abscesses, webs, tethering,
and fistulae) with less dependence on
enteroclysis-level bowel distension as is
necessary for optimal CT.

• Adv of CT:
– availability and a slight cost differential
• Although the overall cost-benefit balance is a key
measure that remains incompletely evaluated.
– Acute situations – critically ill

MRE vs PET or PET/CT
• With regards to the use of PET or PET-CT in the evaluation of CD,
the sensitivity in the detection of active inflammation ranges
between 73% and 90% when compared with clinical, endoscopic or
biological markers of disease activity.
• Using PET alone, there is poor disease localisation, and specificity
can sometimes be low, as other pathological or physiological
processes may lead to increased bowel fluorodeoxyglucose (FDG)
uptake.
• The main disadvantage of PET-CT is the use of ionising radiation;
this is clearly not ideal in young patients who may require repeated
imaging.
• It is also more time consuming to perform than CT or MRI alone.
• Hence for these reasons, PET-CT is not routinely used in the
assessment of patients with CD.

……..in summary
• Multimodality tailored assessment is the rule
rather than the exception in small bowel
imaging , particularly for difficult cases.

Charts illustrate the spectrum of
indications of enterography

Crohn disease
• Crohn disease has a worldwide distribution but is more
prevalent in Europe and North America .
• The peak incidence of Crohn disease is in adolescents
and young adults between 15 and 25 years old; a
second shallow peak is seen in the 50- to 80-year-old
age group.
• Disease is distributed equally between the sexes,
although isolated colonic disease is more common in
women than men.
• Older patients tend to have localized enteritis, whereas
jejunoileitis is more common in younger patients

• The current view is that the diagnosis of Crohn
disease is established by a non strictly defined
combination of clinical presentation; endoscopic
appearance; radiology, histology, and surgical
findings; and, more recently, serology results.
• The varied behaviour and clinical progression of
Crohn disease have led to its subtyping by various
investigators on the basis of inflammatory
activity, clinical indexes, and histopathology
results.

Diagnosis of Crohn Disease and
Assessment of Inflammatory Activity
• Crohn’s disease can
involve any portion of
the gastrointestinal
tract from the mouth to
the anus, although the
small bowel is the most
commonly affected
portion of the bowel,
particularly the distal
and terminal ileum.
Thirty-eight-year-old male with Crohn’s
disease. Coronal volume rendered image
demonstrates thickening and mucosal
hyperemia of the terminal ileum, a classic
appearance and location for acute Crohn’s
related inflammation;

Classification of Crohn Disease
• Classification by clinical or laboratory data has not been
entirely reproducible.
• Maglinte and colleagues proposed an imaging-based
classification of Crohn disease, which they surmise could
provide useful information when used in combination with
clinical and laboratory data.
• They classify Crohn disease into four broad groups:
– active inflammatory,
– perforating and fistulating,
– fibrostenotic, and
– reparative and regenerative subtypes.
• The imaging findings in these subtypes are based on the
detection of ulceration, fistulas, bowel edema, strictures,
and extraintestinal abnormalities.

Active Inflammatory Disease
• This subtype of disease is characterized by:
– inflammation with superficial and deep ulcers,
– transmural inflammation with granuloma
formation, and
– mural thickening.

• Several enterographic findings are associated
with increased disease activity, including
(a) wall thickening greater than 4 mm,
(b) intramural and mesenteric edema,
(c) mucosal hyperemia,
(d) wall enhancement (and enhancement pattern),
(e) vascular engorgement, and
(f) inflammatory mesenteric lymph nodes (often
with hyperenhancement)

(a) Active distal ileal Crohn’s disease in a 36-year-old male. Coronal CT enterography image
showing mural thickening and mucosal hyperenhancement (long arrows). Compare the normal
enhancement of the unaffected small bowel (short arrow).
(b) Enlarged vasa recta involving the actively inflamed neoterminal ileum producing a comb sign
(arrows). Note the presence of enlarged mesenteric lymph nodes.

Perforating And Fistulating Disease
• transmural ulceration and fistula formation,

Fibrostenotic Disease
• This subtype of disease is characterized by
bowel obstruction.
• A fixed narrowing of the affected segment
without any significant bowel wall thickening
or inflammation is typically seen.
• MR fluoroscopy may also show fixity of the
affected segment with proximal dilatation of
the bowel.

33-year-old woman with known Crohn
disease and previous ileocolic resection.
A, Coronal true fast imaging with steady-state
shows thickened neoterminal ileum (arrow).
Note dark submucosal band and relative lack
of inflammation.
This band was proven to be fibrotic stricture
secondary to chronic Crohn disease.
B, Photograph of resected specimen shows
fibrotic stricture (arrow).

• Chronic fibrotic strictures are typically hypointense on both
T1- and T2- weighted sequences, whereas acute
inflammatory strictures due to acute inflammatory edema
show the target sign.
• Fibrotic strictures may show minor, inhomogeneous
enhancement without any evidence of edema or
surrounding mesenteric inflammation or hyperemia.
• Asymmetric bowel fibrosis and shortening secondary to
ulceration of the mesenteric side of the bowel lead to the
formation of pseudosacculations on the other side.
• The ability of tissue contrast differentiation on MRI is
particularly suited to distinguish between a fibrotic stricture
that may require surgical intervention and an acute
inflammatory stricture that may benefit from medical
treatment.

Fibrostenotic Crohn disease.
Axial balanced SSFP MR images without (a) and with (b) fat suppression show low-signal-intensity
duodenal wall thickening (arrows) and proximal obstruction.

Reparative or Regenerative Disease
• This subtype is characterized by
mucosal atrophy and the presence of
regenerative polyps.
• Luminal narrowing may be seen, but
usually there are no signs of
inflammation or obstruction.
• Mucosal denudation with focal areas
of sparing is seen on imaging.
• Typically, reparative polyps do not
show significant hyperemia or mural
edema.
• Extensive filiform polyposis may be
seen in chronic Crohn disease as
multiple filling defects extending into
the lumen without an obstructive
element or significant enhancement.
Wall thickening mainly at the expense of the
submucosa (white curved arrow), which appears
hypointense on the axial T2 fat-suppressed image,
reflecting fat hypertrophy and fibrosis in the setting
of the regenerative---reparative subtype.
The serosa (blue arrow) and mucosa appear
hyperintense producing the halo sign.

Complications
• Segments affected by Crohn
disease are at increased risk
of developing
adenocarcinoma, and the
risk of colorectal cancer in
patients with Crohn colitis is
4–20 times higher than that
of the healthy population.
• Furthermore, segments of
bowel that are not
functioning have a higher
risk for developing cancer.
71-year-old woman with known Crohn
disease.
Coronal true fast imaging with steady-state
shows large mass arising from jejunum (arrow)
with adjacent lymphadenopathy.
Pathology results showed that mass was
adenocarcinoma arising from segment affected
by Crohn disease.

• Carcinomas usually present as stricture lesions that may be difficult to
differentiate from benign fibrotic strictures.
• Neoplastic lesions tend to have longer strictures and may occur in
noninflamed segments of bowel.
• Although reactive nodes are commonly noted in patients with active
Crohn’s disease, large nodes (> 2 cm) should raise the possibility of an
underlying malignancy.
• Any fixed site of narrowing (whether inflammatory or fibrotic) should be
treated as a site of suspicion until proven otherwise, even if a discrete soft
tissue mass is not identified.
• Moreover, asymmetric wall thickening and irregularity should not
automatically be assumed to simply represent a site of active
inflammation, particular if mural stratification of the wall is not seen.
• Bowel cancer must be suspected when bowel obstruction in Crohn disease
does not respond to conventional treatment.

• In a series by Soyer et al, four different patterns
were seen with Crohn’s related small bowel
adenocarcinomas:
1. focal soft tissue mass;
2. short severe stenosis;
3. long stenosis with wall irregularity; and
4. irregular circumferential wall thickening of a bowel
loop.

Lymphoma has been reported to present as multifocal areas of
increased nodularity and strictures on barium examinations.
• Fifty-one-year-old female
with a history of Crohn’s
disease.
• Axial image demonstrates
nodular soft tissue
thickening (arrows)
surrounding an
aneurysmally dilated loop
of bowel in the right
abdomen.
• This was found to represent
B-cell lymphoma following
surgical resection.

Clinical applications of MRE in Crohn’s
disease
• Evaluation of the extent of small bowel disease at
diagnosis
• Evaluation of disease burden in symptomatic patients
to direct therapeutic management
• Evaluation of fibro-stenotic disease, which may
respond better to surgery than to escalation of medical
therapy
• Confirmation of clinical remission and consideration for
escalation of medical therapy if there is persistent
submucosal disease despite clinical remission
• Evaluation of intra-abdominal complications, including
fistulae, tethering, stenosis, and abscesses
• Evaluation of perianal disease

Enterography Beyond Crohn’s
• Small Bowel Obstruction
• Occult GI bleed
• Ulcerative colitis
• Small bowel Neoplasms
– Primary (benign, malignant) & Secondary
• Inflammatory conditions
• Infectious conditions
• Diverticular disease
• Systemic sclerosis
• Bowel duplication
• Familial Mediterranean disease
• Incidental findings

Small-Bowel Obstruction
• The diagnosis of small-bowel obstruction at
enterography is based on:
– the identification of dilated loops of bowel
proximal to the level of obstruction,
– a distinct transition point, and
– a normal-caliber or collapsed distal bowel
segment.

• Abdominal CT has been shown to have high sensitivity
for detection of acute high-grade small bowel
obstructions, and because of its widespread
availability, it is routinely used in clinical practice. MR
imaging also has been shown to be useful for detecting
bowel obstructions in acute settings and differentiating
malignant from benign causes.
• However, conventional cross-sectional imaging
methods (CT, MR imaging) may fail to depict a cause in
a substantial number of patients with symptoms of
intermittent low-grade small-bowel obstruction.

• Studies have shown that CT/MR enteroclysis is
superior to abdominal CT/MR for detection of
transition points because of its improved
distention.
• MR enteroclysis provides improved distention
of the small bowel and may demonstrate
subtle transition points or an obstruction that
may not be visible at imaging with more
routine methods, including enterography.

Low-grade obstruction caused by adhesions.
(a) Axial MR enterographic image shows a distorted small-bowel loop (arrow) in the right lower quadrant,
without obstruction.
(b) Axial image from follow-up MR enteroclysis with improved bowel distention (arrowhead) shows a
persistent focal transition point (arrow) indicative of a proximal obstruction.
These findings are suggestive of an adhesion, the presence of which was confirmed at laparoscopy.

• However, functional cine MR as part of an MR
enterography examination depicts
physiological peristalsis and normal bowel
motion within the abdomen, including
“visceral slide,” which is the normal
movement of bowel loops relative to each
other (Lienemann et al. 2000).

Postoperative Adhesions
• The most common cause of small-bowel
obstructions.
• Adhesive ileal obstruction in a 30-year-old
woman with a history of appendectomy and
recurrent low-grade bowel obstruction.
• MR enterography was performed after the
administration of 1 L of an oral contrast agent.
• Coronal FISP image from MR enterography
demonstrates ileal loop dilatation (curved
arrow), a transition point (straight arrow), and
normal distal caliber (arrowhead).
• No mass, bowel wall thickening, stricture, or
other specific cause of obstruction was
identified.
• These findings were suggestive of an
obstruction due to bowel adhesion, which was
later confirmed at laparotomy.

• Other possible causes of small-bowel
obstruction include:
– inflammatory diseases,
– benign and malignant tumors,
– intussusception,
– strangulated hernia,
– volvulus, and
– radiation-induced enteritis.

Brunner gland hamartoma in a 58-year-old woman with GI tract
bleeding and recurrent low-grade bowel obstruction.
Initial MR enterographic sequences were applied after
administration of 500 mL of an oral contrast agent.
(a) Axial FISP image from MR enterography shows jejunal
intussusception (arrowheads) and narrowing with
resultant obstruction (arrow).
(b) Coronal FISP image from MR enterography shows the lead
point for intussusception: a multicystic lesion
(arrowheads).
(c) Photograph shows the resected jejunal lesion. The diagnosis
at histopathologic analysis was Brunner gland hamartoma.
(Scale is in millimeters.)

Occult Gastrointestinal Bleeding
• Bleeding from the upper GI tract/colon, if it is
reachable by endoscope, is well evaluated.
• Gastrointestinal bleeding from the small intestine is
less common but is difficult to diagnose by
endoscopy or conventional imaging.

Multi-phase CTE
• Scanning is performed from the diaphragm to the
symphysis pubis during each of 3 phases, with scanning
initiated when a region-of interest attenuation
threshold in the aorta is reached.
• During the arterial phase (bolus-triggered) , vascular
ectasias such as AVMs and their early draining veins
are seen.
• The enteric phase (20 seconds after trigger), often
highlights enhancing tumors, with
• The delayed images (70 seconds after trigger) showing
that iodinated contrast is accumulating in the small-bowel
lumen, indicating active bleeding.

Active bleeding at multiphase CT
enterography. (A) Arterial, (B) enteric, and (C)
delayed phase images show progressive focal
contrast accumulation (arrows in A, B, and C)
in an ileal angiodysplasia confirmed at
intraoperative endoscopy.
(C) Additional focus (arrows) of contrast on
delayed image is also presumed to be active
bleeding.

• CT enterography misses some lesions, such as
flat arteriovenous malformations that may be
seen on capsule endoscopy.
• On the other hand, CT can show active
extravasation of contrast into the bowel
lumen.
• CT enterography shows promise as a
complementary study to capsule endoscopy
in this setting.

A heart transplant recipient who presented with abdominal pain and gastrointestinal bleeding.
(A and B) CT shows (A) an intramural small bowel hematoma and (B) a partial small bowel obstruction.
(B) In the more caudal section, note the high-attenuation mural hematoma and the narrowed lumen, which
caused the bowel obstruction.

Ulcerative Colitis
• Because enterography is less sensitive than
endoscopy and principally allows evaluation of
the small bowel, it is not used for the
diagnosis or staging of ulcerative colitis

Active ulcerative colitis with “backwash” ileitis in a 28-year-old woman who presented with
intermittent nausea, vomiting, fever, and chills.
(a) CT enterogram shows a patulous ileocecal valve (arrows), as well as
mural hyperenhancement in the cecal wall (arrowhead).
(b) Transverse CT enterographic images demonstrate pseudopolyps as enhancing tags arising
from the luminal mural surface.

Mural stratification, dilatation of the vasa recta, colonic wall
thickening, and inflammatory pseudopolyps are seen in both
ulcerative colitis and Crohn colitis
Ulcerative Colitis Crohn’s Colitis
Crohn colitis in a 43-yearold woman. CT enterogram
demonstrates Crohn colitis as mural stratification with
intramural edema, bowel wall thickening (arrows),
and dilatation of the vasa recta (arrowheads).
Coronal reformatted CT enterographic images
demonstrate mural hyperenhancement in the
colonic wall and pseudopolyps as enhancing
tags arising from the luminal mural surface.

• When these findings occur in the right colon and
terminal ileum, Crohn disease is more likely.
• In addition, extraenteric complications such as
fistulas, abscesses, or discontinuous colonic or
small bowel inflammation support the diagnosis
of Crohn disease.
• Because of the sensitivity of enterography for
Crohn disease, the principal role of this modality
in patients with suspected ulcerative colitis is to
help exclude findings of Crohn disease such as
small bowel inflammation.

Small-Bowel Neoplasms
• As at CT, differentiation between benign and
malignant small-bowel lesions at MR imaging
may prove difficult, particularly when lesions are
small.
• Factors they found to be associated with
malignancy were:
– the presence of a long, solitary, non-pedunculated
lesion;
– mesenteric fat infiltration; and
– mesenteric lymph node enlargement.

• An advantage of MR imaging over CT for the
detection of small-bowel masses is the ability
of MR imaging to generate images with
different gradations of luminal contrast
agents.
• The use of biphasic enteric contrast agents at
MR imaging further helps in the detection of
subtle masses.

Benign Tumors
• Adenomas
– most common asymptomatic benign tumors of the small
bowel
– most often seen in the duodenum.
– may have malignant potential.
– The tumors appear as well-defined sessile or pedunculated
soft-tissue masses that are surrounded by clear fat planes.
– They show homogeneous moderate enhancement after
the administration of an intravenous contrast medium.
– Adenomas may protrude into the small-bowel lumen
without obstructing it

Lipomas
• Most are seen in the
distal small bowel.
• They commonly arise in
the submucosa and
manifest with
intussusception or
bleeding.
• They display high signal
intensity on T1- and T2-
weighted MR images,
with loss of signal
intensity when fat
suppression is used.
Jejunal intussusception due to a lipoma in a
63-year-old woman. Axial gadolinium-enhanced
T1-weighted fat-suppressed 3D VIBE
image from MR enterography shows
intussusception of a proximal small-bowel
segment. The lead point (arrow) is an ovoid
lesion with low internal signal intensity, a
finding suggestive of a lipoma. The diagnosis
was confirmed at pathologic analysis.

Small-bowel hemangiomas
• consist of either capillaries or cavernous vessels,
most commonly manifest with acute or chronic GI
tract bleeding.
• At MR imaging, small-bowel hemangiomas
appear as submucosal polypoid tumors.
• It may be difficult to differentiate them from
other vascular tumors or malformations on the
basis of imaging criteria alone.
• Angiodysplasia usually appears as an avidly
enhancing plaque or nodule with fading during
the delayed phase

Peutz-Jeghers syndrome
• A genetic disorder with an autosomal dominant
pattern of inheritance, is distinguished by
multiple hamartomatous polyps throughout the
GI tract, mostly in the small bowel, along with
pigmented mucocutaneous lesions.
• The two main problems in the management of
the GI tract lesions in patients with Peutz-Jeghers
syndrome are the longterm cancer risk and
polyp-related complications.

• It is now widely accepted that
patients with the syndrome
have increased risks for many
cancers, including small-bowel
cancers, with a lifetime
incidence of malignancy
approaching 60%.
• Large Peutz-Jeghers polyps (>15
mm) in the small bowel
commonly manifest at an early
age with complications such as
GI tract bleeding, anemia, and
intussusception or obstruction.
• Hence the need for surveillance.
On a CT enterogram obtained in a 17-year-old
boy who presented with signs of intestinal
obstruction secondary to intussusception,
multiple juvenile hamartomatous polyps
(arrows) are visible within the ileum.

• Benign hamartomatous polyps are found throughout
the small intestine, especially the jejunum, in patients
with Peutz-Jeghers syndrome.
• FISP and gadolinium-enhanced fat-suppressed VIBE are
the most useful MR imaging sequences for detecting
small-bowel polyps.
• Polyps appear as hypointense filling defects on FISP
images and typically show marked enhancement
similar to that of the bowel wall mucosa after the
intravenous administration of a gadolinium chelate.

Surveillance of polyps in a 27-year-old man with Peutz-Jeghers syndrome.
(a) Coronal FISP image from MR enterography shows at least three low-signal-intensity polyps
(arrows) in the small bowel.
(b) Coronal gadolinium-enhanced T1-weighted fat-suppressed 3D VIBE image from MR
enterography shows moderate to marked enhancement of the polyps (arrows).

Gastrointestinal Stromal Tumors
• The most commonly occurring mesenchymal neoplasm of
the GI tract.
• The most frequent sites of GISTs are the stomach (60%) and
the small bowel (30%).
• The tumors are usually solitary but have been reported to
occur in multiples, particularly in the setting of type 1
neurofibromatosis
• GISTs in the small bowel most often originate from the
muscularis propria and frequently involve the outer
muscular layer of the bowel wall, exhibiting an exophytic
growth pattern; less frequently, they arise intraluminally.
• Most (70%–80%) of the tumors are benign, but 20%–30%
are malignant

• A GIST often manifests as an
exoenteric, rounded mass that
expands the small-bowel wall with
a smooth, broadly pushing border;
however, endoluminal
development of the tumor is also
possible.
• The tumor may show evidence of
internal hemorrhage or necrosis,
but satellite adenopathy is lacking.
• Small tumors usually enhance
markedly.
• In lesions with extensive regions of
hemorrhage or necrosis, cavities
may form that communicate with
the digestive lumen and contain
air.
Gastrointestinal stromal tumor. CT enterogram
shows an exoenteric gastrointestinal stromal
tumor (arrows) of the duodenum.

Duodenal GIST in a 21-year-old man with type 1 neurofibromatosis. MR enterography was performed for
small-bowel assessment after a small GIST was seen at gastroduodenal endoscopy.
(a) Axial gadolinium-enhanced T1-weighted fat-suppressed 3D VIBE image from MR enterography shows a
large (2-cm), well-delimited exophytic duodenal lesion (arrow).
(b) Diffusion-weighted MR image obtained with b of 800 sec/mm2 optimally displays the high-signal-intensity
lesion against a suppressed background.

• Leiomyomas are
mesenchymal tumors that
also may manifest with
bleeding in the small
bowel but, unlike GISTs,
do not express the c-Kit
protein.
• They are sharply defined
spheroid or ovoid masses
with a maximal diameter
of 1–10 cm that usually
enhance after the
administration of an
intravenous contrast
medium
Leiomyoma in a 60-year-old woman referred for evaluation
of unexplained GI tract bleeding and anemia.
(a) Axial T2-weighted half-Fourier RARE image from MR
enterography shows a round, homogeneous, exophytic ileal
mass (arrow).
(b) Photograph of the resected bowel segment shows a well-delimited
extraluminal mass arising from the bowel wall.
(Scale is in centimeters.)

Malignant Tumors
• Malignant tumors of the small bowel account
for 1%–2% of all GI tract neoplasms and are
usually misdiagnosed at initial presentation or
diagnosed late in the disease process.
• An estimated 60%–70% of symptomatic small-bowel
tumors prove to be malignant

Adenocarcinomas
• most common primary
malignancies of the small
bowel, accounting for 40%
of malignancies in this part
of the GI tract.
• They most often arise in the
duodenum (50%), followed
by the jejunum (30%) and
ileum (20%).
• Adenocarcinomas typically
involve a short segment of
bowel, and they may lead to
partial or complete bowel
obstruction. Adenocarcinoma of the jejunum in a 33-year-old
man. CT enterogram demonstrates a bulky,
heterogeneously enhancing mass (arrow) arising
from the proximal jejunum (arrowhead).

• MR enterographic features of adenocarcinomas include:
– annular and constricting lesions;
– eccentric or circumferential wall thickening with irregular
borders; and
– moderate, sometimes late enhancement after the
administration of intravenous contrast material.
• Lymph node enlargement is not as marked in the presence
of adenocarcinomas as it is in the setting of lymphomas.
• Metastases from bowel adenocarcinomas to local lymph
nodes, liver, peritoneal surfaces, and ovaries may be
depicted at MR enterography

Pathologically proved jejunal adenocarcinoma in a 57-year-old man with abdominal pain and
vomiting for 15 days.
(a) Coronal T2-weighted half-Fourier RARE image from MR enterography shows a
low-signal-intensity jejunal loop with irregular short-segment circumferential thickening and stenosis
(arrow) and a dilated jejunal loop with some degree of ischemia proximal to the stenosed segment (arrowheads).
(b) Coronal gadolinium-enhanced T1-weighted fat-suppressed 3D VIBE image from MR enterography
shows moderate enhancement of the lesion (arrow).

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