Relevance of incidental colorectal FDG-PET/CT-enhanced lesions

Positron emission tomography/computed tomographies (PET/CTs) may result in incidental findings of fluorodeoxyglucose (FDG)-avid lesions in the colon. The aim of this study was to assess the relevance of a colonoscopic workup of such lesions.

We retrospectively analysed all PET/CT reports (n = 4,973) generated in our nuclear medicine department between May 2006 and May 2011; in 69 cases a colonoscopic evaluation was recommended for incidental FDG-avid lesions.

Of these 69 cases, 51 underwent colonoscopy because of the potential need for further treatment. The maximum standardized uptake values (SUVmax) ranged from 5.0 to 42.0 with an average of 10.9. In 44 of the 51 patients, a histopathological abnormality was found on colonoscopy, 44 in the location described by PET/CT. A further 38 lesions were identified that were not visible on PET/CT. The histopathological evaluation in the 51 patients revealed 14 hyperplastic polyps, 27 adenomas with low-grade and 4 with high-grade dysplasia, 3 adenocarcinomas and 1 neuro-endocrine tumour.

Incidental findings of focal colorectal FDG uptake should lead to further workup with colonoscopy. The SUVmax was not predictive for higher grade histologies. With an SUV of 5 the yield was high for colonic premalignant and malignant lesions. However, malignancy cannot be ruled out in focal lesions with an SUV of less than 5, and for individual patients a colonoscopy should not be ruled out.