Discussion about role, indications and limitations of imaging in patients presenting with acute abdomen. Appropriateness criteria are also included.

1. Imaging Acute Abdomen
Part 1: General Concepts
Rathachai Kaewlai, M.D.
www.RiTradiology.com
Updated: May 2009
1

2. Overview
Role, indications and limitations of each
imaging modality: radiography, US, CT, MR
imaging, scintigraphy
Appropriateness criteria
2

3. Acute Abdomen:
A Clinical Challenge
“Severe abdominal pain develops over a
period of hours”
Common chief complaints:
In USA, stomach and abdominal pain ranked first in patient
presentation to emergency departments
Difficult diagnosis:
Broad differentials
Nonspecific history and clinical examination
Nonspecific lab tests
3

4. Acute Abdomen:
A Clinical Challenge
Require all resources to reach accurate
diagnosis, timely management and proper
disposition
4

5. Conventional Radiography
Often the first imaging evaluation
“Acute abdominal series”
Upright chest to evaluate for pneumonia, subdiaphragmatic
pneumoperitoneum
Upright and supine abdomen
Decubitus view of abdomen if upright
radiograph not possible
To detect small pneumoperitoneum
The patient must be in decubitus position for several minutes before
radiograph taken to allow relocation of pneumoperitoneum to
perihepatic space
5

6. Conventional Radiography
Helpful for the detection of:
Pneumoperitoneum
Bowel obstruction
Pneumonia mimicking abdominal pain
Suspected emphysematous pyelonephritis or emphysematous
cholecystitis on ultrasound
6

7. diaphragm
diaphragm
liver
Large pneumoperitoneum: supine chest radiograph in a 70-year-old man
shows a large amount of pneumoperitoneum under the dome of the
diaphragm bilaterally. The patient had perforated stomach following biopsy.
7

8. Small bowel obstruction: Supine and upright abdominal radiographs show
disproportionate dilatation of small bowel (SB) with a relatively small amount
of colonic gas (C). There are air-fluid levels (arrows) with different height in
the same small bowel loops. Small bowel obstruction due to adhesion
8

9. Conventional Radiography
Pitfalls/Limitations
Poor sensitivity to detect several causes of acute abdomen
including appendicitis, cholecystitis and diverticulitis
Poor sensitivity to detect small pneumoperitoneum and free fluid
Low interobserver agreement on the diagnosis of bowel
obstruction (particularly with low-grade small bowel obstruction)
9

10. free air
Small pneumoperitoneum not detected on chest radiograph: Axial CT
image of the upper abdomen shows small dots of extraluminal air in the
omentum (long arrow) and gastrohepatic ligament (short arrows) in a 54-year-
old man who had perforated gastric ulcer.
10

11. SB
SB
“Pseudo” small bowel obstruction on radiography: Supine abdominal
radiograph shows multiple loops of dilated small bowel (SB) with paucity of
colonic gas. Coronal CT image of the abdomen performed on the same day
does not show evidence of bowel obstruction.
11

12. Ultrasound
Right upper quadrant (RUQ) ultrasound
Renal ultrasound
Abdominal ultrasound
Limited ultrasound
12

13. RUQ Ultrasound
Evaluation of biliary tree (i.e. liver, intrahepatic
biliary duct, common bile duct and
gallbladder), pancreas, right kidney
Indications
Right upper quadrant pain attributed to hepatobiliary tract
Imaging of choice to evaluate acute cholecystitis
Intra/extrahepatic biliary duct dilatation
Right hydronephrosis, calculi
13

14. gallstone
Acute cholecystitis: Sagittal ultrasound image of a 63-year-old man
presenting with right upper quadrant pain shows an impacted gallstone in
the gallbladder neck and a positive sonographic’s Murphy sign.
Surgically and pathologically proven acute cholecystitis.
14

15. A B
“double duct” dilated CBD
Biliary ductal dilatation: (A) Transverse grey-scale ultrasound image of the
liver shows a “double-duct” sign (between arrows). They represent a dilated
intrahepatic duct and a portal vein branch. In a normal subject, a portal vein
is the only structures in portal triads visualized in the periphery of the liver.
(B) The color Doppler image of the same patient shows a dilated common
bile duct anterior to the main portal vein. Obstructive biliary system due to
pancreatic head cancer.
15

16. RUQ Ultrasound: Limitations (1)
Recent meal (within 4-6 hours) will contract
gallbladder, therefore:
Limiting evaluation for gallstones
May lead to ‘false-positive’ thickening of gallbladder wall
Recent morphine will contract gallbladder and
mask the presence of sonographic Murphy’s
sign
16

17. RUQ Ultrasound: Limitations (2)
Limited evaluation in patients with
Obesity (poor ultrasound beam penetration)
Fatty liver (obscuring liver pathology)
Significant bowel gas (obscuring pancreas)
Low sensitivity to detect CBD stones (CBD
often cannot be visualized in its entirety)
17

18. liver
gallbladder
Severe fatty liver: Transverse ultrasound image of the liver shows marked
attenuation of the liver echo due to the presence of fatty change. Internal
structures of the liver (i.e. hepatic veins, portal veins, bile ducts) cannot be
visualized.
18

19. dilated CBD
CBD stones
Common bile duct stone not detected on ultrasound: An ultrasound image
of the right upper quadrant shows a dilated common bile duct (CBD), and
intrahepatic duct (not shown) in a 76-year-old man with acute pain and mild
jaundice. Follow-up ERCP shows multiple CBD stones obstructing the CBD.
19

20. Renal Ultrasound
Evaluation of kidneys and bladder
Acute indications:
Hydronephrosis
Renal infection (pyelonephritis is not an imaging diagnosis
although US can occasionally suggest the diagnosis)
20

21. hydronephrosis
hydroureter
Hydronephrosis due to obstructed upper ureteric stone: Sagittal
ultrasound image of the right kidney shows dilated renal collecting system
and proximal ureter in a 57-year-old man presenting with acute renal failure.
He had bilateral hydronephrosis due to obstructing ureteric stones.
21

22. Abdominal Ultrasound
Evaluation of hepatobiliary tract, both kidneys,
spleen, +/- aorta and IVC
Acute indications:
Patients contraindicated or unable to undergo CT or MR imaging
Pregnant patients with trauma
Pediatric patients with abdominal pain
22

23. Limited Ultrasound
Ultrasound performed at specific anatomic
location(s) according to clinical suspicion
Free fluid in trauma patients (FAST)
Suspected appendicitis
Suspected intussusception in pediatric patients
23

24. 4
1 2
3
Diagram showing the areas included in FAST (focused abdominal
sonography for trauma). These four areas are 1) perihepatic and hepato-
renal space, 2) perisplenic, 3) pelvis, and 4) pericardium.
24

25. hyperemia of appendix
non-compressible appendix
A B
Acute appendicitis: (A) Transverse ultrasound image of the right lower
quadrant, using a “graded compression” technique, shows a dilated fluid-
filled tubular structure, which is non-compressible. (B) Color Doppler image
shows hyperemia of the inflamed appendix.
Surgically- and pathologically-proven acute appendicitis.
25

26. mass
mass
intussuscepted
omental fat
A B
Ileocolic intussusception: (A) Transverse ultrasound image of the right
lower quadrant of a 6-month-old boy shows a mass containing several
concentric rings of hyperechogenicity. (B) Longitudinal scan of the “mass”
shows a “pseudo-kidney” sign of intussusception. Hyperechoic region
inside the mass represents intussuscepted mesenteric fat.
26

27. Computed Tomography (CT)
Evaluation of the whole abdomen and pelvis is
required
Options:
Without oral or IV contrast (urinary tract stone, retroperitoneal
hematoma)
With oral and without IV contrast (cannot receive IV contrast)
With IV and without oral contrast (mesenteric ischemia, high-grade
small bowel obstruction)
With both oral and IV contrast (most indications)
With rectal contrast (appendicitis, colonic pathology i.e. penetrating
trauma)
27

28. Computed Tomography (CT)
Indications
Contraindications
Inappropriate use
History of severe contrast reaction (CECT*)
Renal insufficiency (CECT)
Concerns
Use of iodinated contrast medium: nephrotoxicity, adverse
reactions
Radiation exposure
*CECT = contrast-enhanced CT
28

29. Value of CT in Acute Abdomen
Changes leading diagnosis
Changes were shown to be as high as 1/3 of all cases in
prospective investigations1,2
Increases physician’s diagnostic certainty
CT doubled diagnostic certainty of ED physicians, particularly in
the elderly
Changes patient management plan
CT influenced disposition in up to 60% of cases1,2
1. Nagurney JT, Brown DF, Chang Y, et al. J Emerg Med. 2003;25:363-371.
2. Rosen MP, Sands DZ, Longmaid HE, et al. AJR Am J Roentgenol. 2000;174:1391-1396.
29

30. CT - Intravenous Contrast
Often required in acute abdomen imaging
Iodinated contrast medium enhances visibility
of vascular structures and organs
Characters
Water-based
Non-ionic (mostly used at present) vs. ionic
Less osmolality - decreases adverse reactions and side effects
More hydrophilic - less tendency to cross cell membranes
30

31. CT - IV Contrast Reactions
Can range from minimal (e.g. hives) to
anaphylactoid reactions; mostly idiosyncratic
(unpredictable, not dose-dependent)
Acute or delayed
Delayed reaction = 1 hour to 7 days after injection; usually mild
Incidence1
Mild reactions up to 3% (LOCM), 15% (HOCM)
Severe reactions 0.04% (LOCM), 0.22% (HOCM)
Fatal reactions exceedingly rare in both (1:170,000)
LOCM = low-osmolar contrast medium; HOCM = high-osmolar contrast medium
1. Morcos SK, Thomsen HS. Eur Radiol 2001;11:1267-1275.
31

32. CT - IV Contrast Reactions
Predisposing Factors1 x Risk
History of asthma or bronchospasm 6-10
Previous reaction to iodinated contrast medium 5
History of allergy of atopy 3
Dehydration, cardiac disease, hematologic/metabolic
conditions, very young or old age, use of N/A
medications such as b-blockers, IL-2, aspirin,
NSAIDs
1. Morcos SK, Thomsen HS. Eur Radiol 2001;11:1267-1275.
32

33. CT - Premedication
If the risk exists - the patient should be pre-
medicated.
Regimen 1 Regimen 2
Medication Prednisolone Methylprednisolone
Route oral IV
Dose 50 mg 125 mg
Schedule 13, 7, and 1 hour prior to CT 6 and 1 hour prior to CT
Diphenhydramine 50 mg oral or IV 1 hour prior to CT
33

34. CT - IV Contrast Nephrotoxicity
“Increase in serum creatinine by more than 25% or 44
umol/l occurring within 3 days following IV contrast
administration and in the absence of alternative
etiology.”
Reduces renal perfusion and injured renal tubular cells
Manifestations
Reduced GFR, proteinuria, oliguria
Persistent nephrogram on conventional radiography or CT
Usually self-limiting and resolve within 1-2 weeks but
it can increase risk of severe non-renal complications
and prolong hospital stay
34

35. CT - IV Contrast Nephrotoxicity
Incidence
0-10% in normal population (normal renal function)
12-27% in patients with pre-existing renal impairment
Predisposing factors
Patient factors: Pre-existing renal impairment,
particularly diabetic nephropathy, dehydration,
congestive heart failure, concurrent nephrotoxic
medications, e.g. NSAIDs
Large dose of IV contrast medium, injection in renal
arteries
35

36. CT - IV Contrast Nephrotoxicity
Prevention
Adequate hydration
Use low- or iso-osmolar contrast media
Stop administration of nephrotoxic medications
for at least 24 hours prior to contrast
administration
Consider alternative imaging methods
36

37. Contrast-induced nephropathy: Coronal CT image of the abdomen
without IV contrast in a 76-year-old man, status post cardiac catheterization
24 hours ago, shows persistent renal nephrograms.
37

38. CT - IV Contrast and Metformin
Patients with pre-existing renal impairment and
are on Metformin are at risk of developing
Metformin-associated lactic acidosis (MALA).
The use of IV contrast in this patient subset
could lead to contrast-induced nephropathy
that in turn worsens MALA
The American College of Radiology
recommends checking the renal function and
patient’s comorbidities for lactic acidosis before
determining if IV contrast could be given
38

39. CT - IV Contrast and Metformin
39

40. CT - IV Contrast: IV Access
Peripheral IV should be used.
Most PICC lines CANNOT be
used for IV contrast
administration
Not designed to allow rapid injection
Risk of line disruption
‘Power PICC’ (as shown in
picture on the right) can be
used.
Image credit: http://home.caregroup.org/centralLineTraining/
40

41. CT - Radiation Exposure
CT accounts for 5% of radiologic
examinations but contributes 34% of
collective radiation dose, worldwide1
Risk of radiation exposures
Deterministic effect: cell death; threshold level specified when
effects would occur; rarely seen with diagnostic x-ray and CT
Stochastic effect: cancer, genetic effects; “linear, non-threshold”
model generally believed; seen with diagnostic x-ray and CT
1. United Nations Scientific Committee on the Effects of Atomic Radiation. 2000 report to the
General Assembly, Annex D: medical radiation exposures New York, NY: United Nations, 2000.
41

42. CT - Radiation Exposure
Effective radiation dose of one abdominal-pelvic
CT scan equals to1
10 mSv, comparable to 3 years of natural background radiation
100 chest radiographs
“Estimated risk of cancer death for those
undergoing CT is 12.5/10,000 population for
each pass of the CT scan through the
abdomen”2
Any efforts to reduce radiation dose from CT
should be done.
1 = http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray#3
2 = Gray JE. Safety (risk) of diagnostic radiology exposures. In: Janower ML, Linton OW, eds. Radiation risk: a primer. Reston, Va:
American College of Radiology, 1996; 15-17.
42

43. MR Imaging
Advantages over CT
High contrast resolution (good for imaging of pelvis, hepatobiliary
tract and pancreas)
No ionizing radiation
Can be performed in pregnancy
Total exam time usually <30 minutes. No contrast needed in most
cases
Limitations
Contraindications for MR: pacemaker, claustrophobia, etc.
Critically ill patients require MR-compatible life support
equipments
43

44. MR Imaging
Scientific evidence for MRI in acute abdomen
still is not extensive
Clinical applications
Suspected acute appendicitis (particularly during pregnancy, and
in children). Note that gadolinium-based contrast agent cannot be
used in pregnant women.
Good results shown for MRI in sigmoid diverticulitis, common bile
duct stone, acute cholecystitis, pancreatitis
44

45. appendix
Acute appendicitis: Axial STIR MR image of the pelvis in a young pregnant
woman shows an enlarged appendix with high signal intensity of the wall
and small periappendiceal fluid.
45

46. Scintigraphy
Major drawback is limited availability in acute
setting; requires efforts to gather a team off-
hours; and limited resolution
Clinical applications
Acute cholecystitis: hepatobiliary scintigraphy1
Higher accuracy and specificity than ultrasound
Reserved for patients whom diagnosis is unclear after ultrasound
Acute pulmonary embolism: ventilation-perfusion (V/Q) scan
Considered V/Q scan in patients with a normal chest radiograph
suspected of having PE when there is a contraindication to CT
scan (renal impairment, severe contrast reaction)
1. Strasberg SM. New Eng J Med 2008;358:2804-2811.
46

47. Acute cholecystitis: Anterior (A) and right lateral (B) images of a HIDA scan
performed at 4 hours after radiotracer injection show no excretion into the
gallbladder. Image credit: MedPixTM
47

48. Acute pulmonary embolism: 55-year-old man. Perfusion lung scan in right
posterior oblique view shows multisegmental defects which do not match
the findings seen on a ventilation scan obtained earllier (V/Q mismatch).
Image credits: Radiographics 2003;23:1521-1539
48

49. Appropriateness Criteria1
Most 2nd Most
Clinical Variant
Appropriate Appropriate
Non-localizing pain, fever, no recent operation CT with contrast X-ray, US, CT without contrast
Non-localizing pain, pregnant, fever US MRI without contrast
RUQ pain, fever, elevated WBC, positive Murphy sign US X-ray, CT
RUQ pain, suspected acalculous cholecystitis Scintigraphy X-ray, CT
RUQ pain, no fever, normal WBC US CT
RUQ pain, no fever, normal WBC, US shows only gallstones Scintigraphy CT
RLQ pain, fever, elevated WBC, adults, typical appendicitis CT with contrast CT without contrast
RLQ pain, fever, elevated WBC, adults and adolescents, atypical presentation CT with contrast X-ray, US, CT without contrast
RLQ pain, fever, elevated WBC, pregnant US MRI without contrast
RLQ pain, fever, elevated WBC, atypical presentation in children (<14 years) US CT with contrast
LLQ pain, typical diverticulitis, old age CT with contrast CT without contrast
LLQ pain, acute, severe CT with contrast CT without contrast
LLQ pain, woman of childbearing age US CT with contrast
LLQ pain, obese patient CT with contrast X-ray, US, CT without contrast
1 = Adapted from the American College of Radiology Appropriateness Criteria. Available at URL: http://www.acr.org/
SecondaryMainMenuCategories/quality_safety/app_criteria/pdf/ExpertPanelonGastrointestinalImaging.aspx
49

50. Conclusions
Imaging plays an increasingly important role in
diagnosis of etiology of acute abdomen
CT is widely used in several acute abdominal
indications; along with ultrasound and MR
imaging
Limitations of each imaging method and
appropriateness criteria should be considered
before selecting an imaging test for a
particular patient
50