Detection of incidental colorectal tumours with 18F-labelled 2-fluoro-2-deoxyglucose positron emission tomography/computed tomography scans: results of a prospective study.

AIM

This study assessed the clinical significance of incidental colorectal 2-fluoro-2-deoxyglucose (FDG) uptake using (18) F-FDG positron emission tomography/computed tomography (PET/CT) scans and evaluated the importance of colonoscopy when incidental colorectal FDG uptake was observed.

METHOD

A prospective study was designed and conducted at a single institution over a 2-year period. In patients undergoing PET/CT scans, all with FDG uptake in the colorectum were assigned to have colonoscopy and biopsy. The value of PET/CT scanning was studied by comparison with the colonoscopy and biopsy results.

RESULTS

Among 10,978 PET/CT scans, one or more focal uptakes of FDG in the colorectum were observed in 148 (1.35%) patients. In 136 valid patients, malignant colorectal tumours and polyps were found in 23.5% and 20.5%, respectively,, while the colon in the other 56% was normal. A higher false-positive rate was found in the right colon compared with the distal colorectum (66.2%vs 36.7%, P = 0.004). A significant increase of the maximum standardized uptake (SUVmax) value was found among normal, polyps and cancer groups. Multivariate analysis revealed that SUVmax was the risk factor for predicting colorectal cancer or polyps and FDG uptake in the right colon was a negative predictive factor for finding cancers or polyps.

CONCLUSIONS

Our study proves the necessity of colonoscopy when incidental FDG uptake is found on PET/CT imaging. The false-positive FDG uptake is more commonly observed in the right colon. Although the SUVmax value is higher in cancer patients, a high SUVmax value does not necessarily result in malignancies.