Figures 1. There is a contrast-enhancing, markedly hypermetabolic (SUV_max 23.0; delayed SUV_max 28.6) circumferential, irregularly thickened-walled stricture in the upper rectum extending to the rectosigmoid junction. Small, <1cm, non-FDG-avid lymph nodes are seen in the right mesorectal fat.

Figure 2. A hypermetabolic (SUV_max 16.3; persistent on delayed, not shown) pedunculated soft tissue nodule is present in the proximal sigmoid colon.

Figure 3. 2 hypermetabolic lesions are seen.

The pathologic basis for the widely accepted model of colorectal carcinoma (CRC) development is the adenoma-carcinoma sequence, underpinned by a number of observations, as below (taken from Kumar V. et al 2005):
- populations with a high prevalence of adenomas have a high prevalence of CRC, and vice versa;
- the distribution of adenomas in the colorectum is comparable to that of CRC;
- the peak incidence of adenomatous polyps antedates by some years the peak for CRC;
- when invasive carcinoma is identified at an early stage, surrounding adenomatous tissue is often present;
- the risk of cancer is directly related to the number of adenomas (hence the virtual certainty of cancer 
   in patients with familial polyposis syndromes);
- programs that assiduously follow patients for development of adenomas and remove all that are suspicious 
   reduce the incidence of CRC.

18F-FDG accumulates in colonic adenomatous polyps. This is usually an incidental finding, as occurred in our case, and justifies a colonoscopy to detect pre- and malignant lesions. The delayed scans were useful in distinguishing pathologic from physiologic bowel activity.

The utility of PET/CT in the evaluation of primary colorectal carcinoma has been shown to alter management in up to 24%, with improved sensitivity and accuracy compared to CT alone. The CT component adds valuable anatomic information to the functional information provided by PET, improving accuracy compared to PET alone.

A feasibility study on PET/CT colonography in patients with colorectal polyps showed that the metabolic information did not improve the accuracy of CT colonography.