Focal Small Bowel FDG Uptake in Cancer Patients Undergoing PET/CT: Prevalence and Etiology.

Abstract

To determine the prevalence, etiology, and clinical significance of incidental focal small bowel FDG uptake in patients undergoing PET/CT for staging of non-small bowel cancers. Retrospective review of consecutive FDG PET/CT examinations obtained for cancer staging with incidental focal small bowel radiotracer uptake was performed. Exclusion criteria included known small bowel pathology or insufficient reference standard. Imaging findings assessed included lesion location, number, CT correlate, SUV max , and presence of metastases outside the bowel. Clinical data included age, sex, cancer clinical setting, origin, and stage. Focal small bowel FDG uptake etiology (benign vs. metastatic) was determined by composite reference standard (histopathology, clinical, and imaging follow-up). Statistical analyses included Wilcoxon rank-sum test, Pearson's χ 2 test, Fisher exact test, and ROC curve analyses. In a review of 147,516 PET/CT examinations, incidental focal small bowel FDG uptake was rare, with a prevalence of 0.1% (88/147,516). Most cases were metastatic, 60.2% (53/88), most commonly spread from lymphoma [32.1% (17/53)] and melanoma [30.2% (16/53)]. Metastatic lesions were evenly distributed throughout the ileum [47.2% (25/53)] and jejunum [39.6% (21/53)]. Metastatic focal small bowel FDG uptake was associated with presence of other sites of distant metastases, higher SUV max , and presence of a CT correlate ( P <0.01). Incidental focal small bowel FDG uptake is rare. Most small bowel hypermetabolic foci are metastatic and are predominantly encountered with melanoma and lymphoma. Multiple imaging and clinical factors helped differentiate between benign and metastatic focal small bowel FDG uptake.