Case of The Month

Presentation

A 40 year old male presents with intermittent rectal bleeding.

Investigations

CT Colonography was performed, which revealed a malignancy. See the images above.

Left Image:  This is a "virtual barium enema" image, showing an annular,  "apple core", narrowing in the sigmoid colon, typical of bowel cancer.

Middle Image: This is an image during  "virtual colonoscopy" obtained from the CT data, showing how the tumour would appear at optical colonoscopy.

Right image: This is a multiplanar reformat, showing the narrowing of the lumen and thickening of the bowel wall, typical of colon cancer.

Further staging was performed with CT of the abdomen and chest, which showed no evidence of abdominal adenopathy, but a non specific 5mm low density lesion of the liver. An MRI scan of the liver proved this to be a simple cyst.

Discussion

CT Colonography (CTC), or virtual colonoscopy, is a low radiation dose CT technique for detecting colonic polyps and tumours. It is not designed for staging cancer or assessing suspected colitis.

The patient's bowel must be cleansed prior to the examination with a bowel preparation agent. The colon is insufflated with CO2 and the patient is then scanned in both the supine and prone position. The acquired images are analysed on a workstation.

As a technique, CTC is comparable to colonoscopy in the detection of large bowel polyps and malignancies, with a sensitivity of about 90 - 94 % for polyps exceeding 10mm in size. Sensitivity for polyps as small as 6mm is also excellent and comparable to that of colonoscopy. Both techniques are far superior to Double Contrast Barium Enema.

CTC also allows diagnosis of colonic diverticulosis as well as the identification of submucosal lesions.

CTC should not be used in the assessment of suspected colitis, including acute diverticulitis (or within 6 to 8 weeks of a suspected episode), as there is an increased risk of bowel perforation. Routine CT abdomen or endoscopy should be used in this situation.

CTC is better tolerated by patients than both Double Contrast Barium Enema and conventional Colonoscopy.

References

Gluecker TM et al Colorectal Cancer Screening with CT Colonography, Colonoscopy, and Double-Contrast Barium Enema Examination: Prospective Assessment of Patient Perceptions and Preferences. Radiology 2003;227:378-384.

Pickhardt PJ et al, Computed Tomographic Virtual Colonoscopy to Screen for Colorectal Neoplasia in Asymptomatic Adults. NEJM 2003; 349:2191-2200