CT colonography in cancer detection: methods and results

Abstract

Colon cancer is the second leading cause of cancer-related death in the Western world. Approximately 80-90% of colon cancers develop in adenomas after mutations. The risk of encountering malignancy increases with the size of the adenomatous polyp. It is approximately 1% in adenomas <1 cm, and increases to 10% for adenomas 1-2 cm, and 20-53% for adenomas >2 cm. CT colonography (CTC) is a new technique, which allows, after bowel preparation and distension of the cleansed colon, to generate a volumetric display of the colon. Multi-detector CTC has a sensitivity of 93-100% and 70-83% for detection of polyps sized >=10 mm and 6-9 mm, respectively. For detection of colorectal cancer, CTC has a sensitivity of 83-100%. CTC is especially of value in patients with incomplete colonoscopy due to stenosis or colon elongation. It reliably detects synchronous cancers proximal to occlusive colon cancers, when colonoscopy fails to evaluate the entire colon. First results of a colon cancer screening study have shown that CTC is equal or even slightly superior to conventional colonoscopy in detection of adenomatous polyps >=8 mm. Moreover, CTC detects clinically significant extracolonic abnormalities not shown by colonoscopy. To increase the patient acceptance for wide-spread application of CTC cancer screening the issue of patient discomfort by bowel preparation and radiation exposure needs to be addressed further.

Figure 1

Fecal tagging of stool with barium. (a) Endoluminal viewing shows two polypoid lesions. The true nature of these lesions can not be assessed with certainty. (b) Axial 2D source image of prone scan (the image is flipped to facilitate comparison with the scan in the supine position) shows fecal material to be very hyperdense (arrow), which allows easy differentiation from true polyps. (c) Axial image of supine scan shows mobility of the ‘polyp’ (arrow).

Figure 2

Distension of the transverse colon: prone vs. supine imaging. (a) In the prone position, the transverse colon is collapsed and cannot be adequately assessed (the image is flipped to facilitate comparison with the scan in the supine position). The ascending and descending colon are adequately distended. (b) In the supine position, there is good distension of the transverse colon to assess the mucosa.

Figure 3

Rectal cancer with liver metastases, and sigmoid polyp. (a) Source image reveals contrast-enhanced rectal cancer (black arrow). There is a small polyp in the sigmoid colon, which turned out to be an adenoma (white arrow). (b) Coronal MPR reveals multiple liver metastases.

Figure 4

Analysis of a small polypoid lesion: identification of sessile fecal material by texture analysis. (a) The 3D endoluminal view shows polypoid lesions, suspicious for true polyps. (b) The 2D source image reveals a tiny air bubble in the polypoid lesion (arrow), typical of stool (arrow).

Figure 5

Surface-rendered image of the entire colon. The path of the virtual colonoscopic ‘camera’ is demonstrated. It is possible to mark lesions found to facilitate orientation of the colonoscopist during endoscopic polypectomy.

Figure 6

Image viewing of a polyp in 2D and 3D. (a) Axial source image reveals the polypoid lesion to be contrast-enhanced, indicative of a true polyp (arrow). (b) Endoluminal viewing shows a polyp.

Figure 7

Detection of stenotic cancer in a patient with polyposis. (a) Coronal MPR shows a stenotic cancer of the right flexure with a typical apple-core appearance (arrow). (b) Endoluminal view shows stenotic cancer.

Figure 8

Detection of synchronous second cancer in a patient with incomplete colonoscopy. The coronal MPR shows a stenotic cancer in the transverse colon (large arrow), which could not be passed during colonoscopy. There is a second tumor in the proximal transverse colon (small arrow).

Figure 9

Stricture in Crohn’s disease. (a) Surface-rendered image shows long and smooth stricture of the transverse colon (arrow) in a patient with Crohn’s disease. (b) 3D viewing of the surface and morphology of the stricture.