Clinical significance of incidental focal bowel uptake on 18F-FDG PET/CT as related to colorectal cancer.

OBJECTIVE: Increased focal colorectal uptake of fluorine-18-fluorodeoxyglucose (18F-FDG) is reported to occur in 1%-3% of patients undergoing 18F-FDG positron emission tomography/computed tomography (PET/CT) for disease outside the bowel. However, there is no consensus on how to deal with this finding in the clinic. Due to the non-specific appearance of such lesions and a certain rate of false positive findings, patients may by subjected to unnecessary invasive procedures or, conversely, cancers may be overlooked if the risk of malignancy is downplayed. The purpose of this study was to examine the incidence and clinical significance of focal colorectal incidentalomas (FCI) at our institution and to assess the potential benefit of using semi-quantitative measures instead of visual interpretation to discern malignant from benign lesions.

SUBJECTS AND METHODS: We identified all patients in 2011 with a report of FCI. We reviewed patient charts with regard to basic characteristics, indications for and results of 18F-FDG-PET/CT and subsequent workup including colonoscopy and histopathological analyses, and applied post hoc semi-quantitative analysis. Out of 4,829 patients, twenty-five met the inclusion criteria (mean age 71 years, 13 females, 12 males).

RESULTS: Of the 25 included patients, eight presented with no pathologic or non-malignant findings (e.g. inflammation), while ten had polyps/adenomas and seven a hitherto undiagnosed colorectal cancer. Semi-quantitative SUVmax values and ROC analysis based cut-off values could not reliably discriminate benign from premalignant or malignant disease.

CONCLUSION: It is the opinion of the authors that 18F-FDG PET/CT scan may identify incidentally sites of colorectal carcinoma but cannot discriminate them from polyps/adenomas. Nevertheless, incidental focal bowel uptake should always be reported and/or further evaluated.