CT Colonography for Surveillance after Colorectal Surgery
Follow-Up after Colorectal Surgery
Surveillance for recurrent and metachronous tumors after surgical resection of colorectal cancer is clinically important because early detection and treatment can increase the survival rate of patients. Recurrence after resection of colorectal cancer can occur in the colon or in extracolonic sites. Local colonic recurrence can be either directly at the anastomosis or near the site of the primary resection. Extracolonic recurrence comprises distant metastases in the liver, lung, peritoneum, etc. Metachronous lesions are colorectal adenomas and cancers that develop later and do not originate from the original cancer.
Current surveillance guidelines generally recommend a combination of clinical examination, serum carcinoembryonic antigen (CEA) testing, optical colonoscopy, and CT of the chest, abdomen, and pelvis (Schmoll et al. 2012). Optical colonoscopy is specifically used for routine postoperative surveillance for local tumor recurrence and metachronous intracolonic lesions. CTof the abdomen and pelvis is performed for surveillance of the extracolonic structures and organs for detection of extracolonic recurrence.
Role of CT Colonography and Examination Technique
CT colonography for postoperative surveillance following curative resection of a colorectal carcinoma has the potential to combine colonic and extracolonic information and may thus be used as an alternative to the combined approach of optical colonoscopy and contrast-enhanced abdominal CT. In fact, recent studies have indicated the usefulness of postsurgical CT colonography after resection of a colorectal carcinoma. In one of the largest series, Kim and colleagues (2010) reported postsurgical CT colonography to be accurate and safe. These authors were able to detect all metachronous colonic carcinomas and 81.8% of advanced neoplasms. On the basis of the reported high negative predictive value, negative results of CT colonography could obviate the need for surveillance optical colonoscopy during the same time frame.
Capabilities of CT colonography. In the vast majority of patients who have undergone colorectal cancer surgery, CT colonography enables complete evaluation of the entire remaining colon. This is particularly necessary for depicting the postoperative anatomy and for detecting metachronous colonic lesions. Furthermore, contrast-enhanced CT colonography allows evaluation not just of the colon, but also, on 2D views, of the pericolic structures and other abdominal organs. Two-dimensional views also provide information about the wall morphology of the anastomosis and the perianastomotic tissue. This is particularly important because most local recurrences at the site of the anastomosis are extraluminal and therefore cannot be detected on optical colonoscopy.
Only one-third to one-half of all local recurrences have an intraluminal component. More than that, over half of all recurrences of colorectal carcinoma occur as distant metastases.
Contrast-enhanced CT colonography can therefore be used to detect local recurrence, metachronous tumors, and metastases in a single examination.
Examination timing. To allow for postsurgical healing of the colon anastomosis, CT colonography should only be performed after an appropriate postoperative interval. As with optical colonoscopy, CT colonography should not be performed earlier than 3 months after colonic surgery.
Examination technique. In patients with a deep rectal anastomosis, the rectal balloon should be distended carefully to avoid injuring the anastomosis. It should also be noted that an inflated rectal balloon may obscure a recurrence at the site of the anastomosis. As a general principle, bowel distension should be performed very carefully in postsurgical patients. The use of intravenous contrast is generally indicated for postoperative surveillance studies. It should be administered in one of the two scanning positions, ideally the supine, during the portal phase.
Colorectal Anastomoses
Colonic, colorectal, or ileocolonic anastomoses may be end to end or end to side. They are placed either by manual surgical suturing or with the aid of a surgical stapler. They are placed either by manual surgical suturing or with the aid of a surgical stapler. Whether manual sutures or surgical stapling devices are used depends on the location of the anastomosis and the surgeon′s preference. In general, anastomoses in rectal surgery are performed with stapling devices, whereas in the more proximal colon both techniques may be used. This is of radiological relevance since manual sutures are barely visible at CT. Surgical staples are sufficiently visible at CT because of their hyperdense structure.
The type of operation depends on the segmental location of the tumor. Typical colonic resections include right hemicolectomy, transverse colon resection, left hemicolectomy, and sigmoid colon resection. Sometimes an extended right or left hemicolectomy is performed. Cecal resection is often performed in inflammatory disease or for large poylps. Rectal surgery includes low anterior resection with a colorectal anostomosis, complete rectal resection with a coloanal anastomosis, and a complete abdominoperineal resection with permanent colostomy.
In a right hemicolectomy, an end-to-end or end-to-side ileotransversostomy is usually placed to restore continuity of the bowel. In a left hemicolectomy, end-to-end anastomosis of the transverse to the sigmoid colon is performed, while in sigmoid resection the descending colon is anastomosed end to end to the rectum. The CT colonographic appearance of normal and abnormal colonic anastomoses was described in 2007 by Choi et al., as described below.
CT Morphology of Colonic Anastomoses
Normal Colonic Anastomosis
A normal colonic anastomosis has a ring-like appearance (Fig. 4.112). On endoluminal 3D views, it may appear as a smooth circumferential ridge or may present a web-like appearance (Fig. 4.113). In end-to-side anastomoses, the blind end is also visible (Fig. 4.114). The edge of the anastomosis may be sharp or blunt; its surface is smooth and regular. On 2D views, the bowel wall presents as a continuous thin linear structure without increased attenuation in the surrounding fat tissue. If a surgical stapler was used, the staples around the circumference of the anastomosis is often easy to identify because of its high attenuation.
Polypoid filling defects, focal or circumferential thickening of the bowel wall or adjacent soft tissue, and pericolic fat stranding are findings suggestive of recurrence and require further investigation.
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