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CT Colonography

Article information

J Korean Med Assoc. 2007;50(1):33-50
Publication date (electronic) : 2007 January 31
doi : https://doi.org/10.5124/jkma.2007.50.1.33
Se Hyung Kim, MD
Department of Radiology, Seoul National University College of Medicine, Korea. shkim@radcom.snu.ac.kr

Abstract

CT colonography is a recent radiologic technique enabling detection of tumoral lesions in the colon. Since double contrast barium enema has lost most of its adherents, CT colonography gives a great opportunity for radiologists to play a predominant role in the diagnosis and treatment of colorectal cancer and adenoma. CT colonography has dramatically evolved by the refinement of the existing techniques and the introduction of new techniques such as fecal tagging, the use of carbon dioxide to inflate the colon, multi-detector row CT scanners, the use of ultra-low dose scan protocols, and computer-aided detection. These technical improvements are helpful both to the radiologists and to the patients. Several technical factors should be considered for the successful performance of CT colonography. Fecal tagging improves patients' compliance by allowing for reduced bowel preparation. It facilitates the differentiation of true polyp from residual feces, resulting in the improvement of diagnostic accuracy. Automated carbon dioxide insufflation is more efficient and safer in colonic distention compared to manual room air insufflation. CT colonography should be performed by using a thin collimation of ≤ 3mm with a reconstruction increment of ≤ 3 mm and a low radiation dose of 30mAs to 50mAs. There are two strategies to interpret CT colonography dataset; primary 2D and 3D interpretation. There is not a single correct method for interpretation of CTC; therefore, the radiologists should be well-versed with both methods of interpretation. Finally, radiologists should also be familiar with potential diagnostic pitfalls, false positive and false negative findings. In experienced hands, CT colonography seems to be ripe for prime-time colorectal cancer screening. However, it is not yet ready for widespread application of screening due to various drawbacks. Therefore, considerable efforts should be undertaken to take it to the level of being a widely accepted screening method for colorectal cancer.

Keywords: Colon; CT; Neoplasm; Technique

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Copyright © 2007 Korean Medical Association

Figure 1

Figure 1

Fecal tagging using 40% high concentration of barium

(A) Stool tagging. Solid stools (arrows) are tagged homogeneously and appear white

(B) Fluid tagging. Residual fluid (arrow) in distal transverse colon is tagged homogeneously and appears white

Figure 2

Figure 2

CT colonography using 3D virtual colon dissection technique. 3D virtual colon dissection technique was developed to inspect the inner colonic surface by virtually dissecting the colon along its longitudinal axis. A 6mm sessile polyp (arrow) is seen in the sigmoid colon

Figure 3

Figure 3

A 6mm sessile polyp

(A) 2D axial CT images. In both supine (left) and prone (right) positions, a sessile polypoid lesion (arrows) having homogeneous soft tissue attenuation is seen without position change in the sigmoid colon

(B) 3D endoluminal images. A polyp shows same shape in both supine (left) and prone (right) positions

(C) Conventional colonoscopic image. This lesion was confirmed as a low grade tubular adenoma on pathologic examination

Figure 4

Figure 4

A 1cm pedunculated polyp

(A, B) 2D axial (A) and 3D endoluminal (B) images. Images in a prone position (left) show a pedunculated polyp (arrow) having a long stalk. The lesion shows collapsed shape on supine images (right)

(C) Conventional colonoscopic image. This lesion was confirmed as a low grade tubular adenoma on pathologic examination

Figure 5

Figure 5

Normal ileocecal valve

(A) On 3D endoluminal image, a polypoid mass-like lesion (arrow) is shown

(B) On 2D axial image with soft tissue window, this (arrow) stands in a characteristic location and possesses homogeneous fatty internal attenuation, indicating ileocecal valve

Figure 6

Figure 6

Diverticula in the ascending colon

(A) 3D endoluminal image shows two diverticular orifices (arrows) projecting from the colonic lumen at the area just proximal to the ileocecal valve (*)

(B) 2D axial CT scan shows focal outpouchings (arrows) of the colonic lumen

Figure 7

Figure 7

Impacted diverticulum

(A) 3D endoluminal image demonstrates a polypoid filling defect (arrow) which is protruded into the colonic lumen

(B) 2D axial CT image with soft tissue window shows the filling defect (arrow) to project beyond the colonic wall into the pericolic fat and contain barium and air, indicating the defect is retained stool and barium within a diverticulum

Figure 8

Figure 8

Colon cancer

(A) On 3D endoluminal image, an irregularly flat and elevated lesion (arrow) is seen

(B) This lesion (arrow) appears an eccentric wall thickening of the colon on 2D axial CT image

(C) Colonoscopic image demonstrates similar appearance to that of 3D endoluminal image. This lesion was diagnosed as a colon cancer after right hemicolectomy

Figure 9

Figure 9

Occlusive colon cancer

(A) 3D endoluminal image depicts a large and irregular mass (arrow) with luminal narrowing

(B) 3D transparency view shows classic apple-core lesion (arrow) in the sigmoid colon

(C) On 2D axial, enhanced CT image, segmental wall thickening (arrow) with abnormal enhancement is seen, indicating sigmoid colon cancer. Note pericolic fat stranding and small lymph nodes around colonic mass. The findings on 2D images enable us to determine local staging of colorectal cancer

Figure 10

Figure 10

Feces showing position change. Image in a supine position (left) shows a small polypoid lesion (arrow) in the transverse colon. In a prone position (right), this lesion (arrow) moved to a dependent portion of the colon, indicating feces

Figure 11

Figure 11

Feces containing air

(A) On 3D endoluminal view, a polypoid lesion (arrow) projecting into the colonic lumen is seen

(B) On 2D axial image with soft tissue window, the lesion (arrow) has typical feature of feces, that is, central pockets of air

Figure 12

Figure 12

Feces with angular margin. 3D endoluminal images demonstrate angular margins of feces (arrows). On the contrary, true polyps show round, oval, or lobulating contour (not shown)