Clinical significance of incidental focal colorectal (18)F-fluorodeoxyglucose uptake: our experience and a review of the literature.

Aim  The aims of the present study were: (i) to evaluate the focal incidental colorectal uptake of 18F-fluorodeoxyglucose ([18F]FDG) and to correlate it with colonoscopy and histological findings; (ii) to evaluate the relationship between the presence/absence of neoplastic disease and clinical data and the anatomical site of [18F]FDG uptake; and (iii) to compare our results with those reported for incidental colorectal uptake of [18F]FDG in the literature and those obtained from various screening programmes for colorectal cancer. Method  The database of 6000 patients referred for [18F]FDG positron emission tomography/computed tomography (PET-CT) to our centre was retrospectively reviewed for incidental colorectal uptake of [18F]FDG. Patients with focal uptake were selected and the aetiology of PET findings was verified with a subsequent colonoscopy and histopathological analysis when available. Results  Incidental colorectal uptake of [18F]FDG was seen in 144 (2.4%) patients, of whom 64 (1.1%) had focal uptake; 48 out of these 64 patients underwent colonoscopy, which showed malignant tumours in 12 (25%), premalignant lesions in 19 (40%), non-neoplastic lesions in six (12%) and lesions not confirmed by colonoscopy in 11 (23%). Our data agreed with previously published data. Statistical analysis did not show any significant relationship between the presence/absence of neoplastic disease and patient sex or age, type of primary disease and anatomical site of [18F]FDG uptake. Comparing our data with various screening programmes, a significant difference was found only with series in which colonoscopy was performed in patients at high risk for colorectal cancer. Conclusion  Focal incidental colorectal uptake of [18F]FDG is observed in about 1% of PET/CT studies and carries a high risk of neoplastic disease. A PET-CT report should suggest colonoscopy when abnormal findings are reported.