CT colonography by Mahmoud Elshamy MD

1. By
Dr/ Mahmoud Elshamy MD

2. INTRODUCTION
 Colorectal carcinoma (CRC) is the Second most
common cancer in United States and second leading
cause of cancer related death
Colorectal Cancer Incidence & Mortality 2000-2003
United States Kentucky
African Americans Caucasians
Incidence
64.4 53.1 61.2
Per 100,000
Mortality
28.4 19.8 23

3. INTRODUCTION
 The benign colorectal polyp is the core of colorectal
cancer

4. HISTOLOGIC CLASSIFICATION
OF POLYPS
 Adenomas are one histologic subtype of colorectal
polyps.
 Other histologic subtypes include mucosal polyps,
hyperplastic/ serrated polyps, juvenile polyps, and
inflammatory polyps.
 In addition, certain types of polyps can arise from
layers deeper than the mucosa, including lipomas,
carcinoid tumors, gastrointestinal stromal tumors
(GIST), and serosal lesions.

5. HISTOLOGIC CLASSIFICATION
OF POLYPS.
 Adenomas constitute approximately half of colorectal
polyps; hyperplastic and serrated lesions make up
about one third or more; and mucosal polyps make up
approximately 10%. The remaining histologic subtypes
constitute only a tiny percentage.
 The histologic classification of polyps cannot be
reliably determined by gross evaluation either at
endoscopy or at CTC; they require pathologic
examination for final diagnosis.

6. POLYP MORPHOLOGY.
 Polyps measuring 3 cm are generally divided into three
major morphologic categories: sessile, pedunculated,
and flat.
 Invasive masses are generally bulky annular or
semiannular tumors.

7.  The ideal target for screening and prevention of
colorectal cancer is the “advanced adenoma,” which is
defined as an adenoma that is large (10 mm) and/or
contains histologic findings of either high-grade
dysplasia or a prominent villous component

8. Methods for Screening
 Colonoscopy
 Air contrast barium enema
 CT colonoscopy

9. Clinical Indications for Performing
CTC
SCREENING INDICATIONS
 Asymptomatic adults at average risk
 Asymptomatic patients with positive family history
 Asymptomatic patients at increased risk for colonoscopy
DIAGNOSTIC INDICATIONS
 Following incomplete optical colonoscopy
 Evaluation of suspected submucosal lesions
 Surveillance of unresected 6-9-mm polyps detected at previous
CTC
 Unexplained GI bleeding, iron deficiency anemia, or other GI
symptoms
 Symptomatic patients at increased risk for colonoscopy
 Surveillance following resection of polyps or cancer

10. CTC TECHNICAL CONSIDERATIONS
The technique for CTC involves the following steps:
 (1) Bowel preperation.
 (2) Colon insufflation.
 (3) Image acquisition.
 (4) Image processing and interpretation.

11. IMAGE PROCESSING AND
INTERPRETATION

12. Large fl at hyperplastic
polyp detected at CTC screening. 3D
endoluminal (A) and 2D transverse
(B) CTC images show a large but
relatively subtle 15-mm nonpolypypoid
lesion (arrowheads) within the
transverse colon. A central depression
is suggested on the 3D view. The
lesion was confirmed at same-day OC
(C) and proved to be hyperplastic.

14. 3D RECONSTRUCTION

15. 3 D VIRTUAL Recontruction

16. 3D RECONSTRUCTION

17. Detection Rates
 Colonoscopy: Sensitivity of 88.2 (>10mm)
Sensitivity of 90.0 (<6mm)
 CT colonoscopy: Sensitivity of 92.2 (>10mm)
Sensitivity of 85.7 (<6mm)
 Air contrast barium enema: failed to identify up to 50% of
polyps greater than 10mm in diameter

18. Virtual vs. Optical Colonoscopy
 Patients reported less discomfort with virtual colonoscopy
 Shorter examination time with VC
 72.3% of patients preferred VC as screening technique
compared to 5% preferred CC as screening technique
 More patients were willing to repeat a VC at shorter
intervals than CC.

19. Benefits Of CT Virtual
Colonography
 Faster examination time and this is a non invasive test.
 It provides three-dimensional images that can depict
many polyps and other lesions as clearly as when they
are directly seen by optical Colonoscopy.
 Reduced patient risk, CT Colonography has a
markedly lower risk of perforating the colon than
conventional Colonoscopy.

20. Limitations of CT Virtual
Colonography
 CT Virtual Colonography is strictly a diagnostic
procedure. If any significant polyps are found, they
will have to be removed by conventional colonoscopy.
 The immediate risks of CTC include a small rate of
perforation related to gas distension, which is lower
than the risk from colonoscopy.
 Potential long-term risk from radiation exposure.