Endoscopic findings in case of incidental colonic uptake in PET-CT How to improve PET-CT specificity ?

Unexpected colonic (18)FDG focal uptakes (UCFU) in PET CT occur in 1.3-3.3% of cases in retrospective study and are often associated with significant colorectal findings in endoscopy, especially neoplastic lesions. The purpose of our prospective study was to evaluate the significance of UCFU and to assess criteria improving PET CT specificity for advanced adenoma and neoplasia. This study was conducted in a single institution from April 2012 to September 2013. In the 2904 patients who benefit from PET CT, 52 had an UCFU and 43 were referred for colonoscopy. After endoscopy, 8 examinations showed no colonic abnormality (18.6%), 7 showed benign lesion (16.3%), 18 showed advanced adenoma (42.9%) and 10 showed carcinoma (23.3%). There were more false positives results in the proximal colon compared to distal colon. Eighteen patients had UCFU and tomodensitometric abnormalities in the same colonic area. This pathological combination was strongly associated to the diagnosis of malignancy. Comparing standardized uptake values (SUV), we showed statistically significant difference between the adenocarcinoma and advanced adenoma groups and a difference at the margin of statistical significance between adenocarcinoma and benign lesion groups. Any cut off value could be determined. In conclusion, we confirmed that UCFU are often associated to endoscopic findings and neoplastic lesions and justify systematic endoscopic exploration. Considering the fragility of oncologic patients, criteria improving PET CT specificity are needed to select endoscopies which should be performed quickly from those who could be delayed. We showed that associated tomodensitometric abnormality and high focal FDG activity are more predictive of a neoplastic lesion.