Prevalence and Clinical Significance of Incidental Focal 18F-FDG Uptake in Colon on PET/CT Imaging.

Objectives: The present study aimed to identify the prevalence of focal uptake in the colon on 18fluorine-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) studies performed for the evaluation of malignancies other than colon, to detect the rate of malignancy in incidental focal 18F-FDG avid colonic lesions and to investigate if any possible role of maximum standardized uptake value (SUVmax) values in the discrimination of malignant lesions from premalignant and benign ones exist. Methods: We retrospectively reviewed the files of 8,017 patients with known or suspected malignancy, who underwent whole-body 18F-FDG PET/CT at our institution during the period November 2017 to November 2019. Patients showing a single site of focally increased colonic 18F-FDG uptake that was more intense compared to liver uptake on 18F-FDG PET studies and referred to colonoscopy were enrolled in the study. Results: Fifty two patients (83.8%) had at least 1 corresponding lesion on colonoscopy, whereas in 10 patients no lesion was detected. Subsequent histopathological examinations revealed no corresponding lesion in 13 (13.7%), a benign lesion in 18 (18.9%), hyperplastic polyp in 10 (10.5%), low-grade polyp in 16 (16.8%), high-grade polyp in 29 (30.5%) and malignant lesion in 9 (9.5%) of the focal 18F-FDG uptake sites. According to histopathology results, statistically no significant difference was found between the SUVmax measurements of malignant and benign cases (p>0.05) but the average SUVmax measurements of malignant cases were found to be significantly higher than lower + high-grade cases (p<0.05) and hyperplastic polyp cases (p<0.01). Conclusion: In conclusion, any unexpected focal 18F-FDG uptake in 18F-FDG PET/CT studies is suspicious for malignancy and should be clarified by colonoscopy. The intensity of 18F-FDG uptake does not preclude the application of colonoscopy and histopathological verification of the lesion if there is any.