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

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 (SUV_max) values in the discrimination of malignant lesions from premalignant and benign ones exist.

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.

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 SUV_max measurements of malignant and benign cases (p>0.05) but the average SUV_max 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).

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.