Frequency and etiology of solitary hot spots in the pelvis at whole-body positron emission tomography/computed tomography imaging

Purpose: To determine the frequency and etiology of a single hypermetabolic focus within the pelvis with no other areas of increased 18-fluorodeoxyglucose (FDG) uptake in the reminder of the whole body in an oncological population. Method and Materials: We retrospectively examined the first 700 whole-body PET/CT scans performed at our institution for baseline staging or follow-up of cancer and identified all patients with a solitary focus of increased FDG uptake in the pelvis. All available medical records and imaging findings in these patients were reviewed in order to determine the etiology of increased FDG uptake. Results: Eight (1.1%) of the 700 patients had a solitary hot spot in the pelvis at positron emission tomography (PET)/computed tomography (CT) imaging, consisting of seven of 380 women and one of 320 men. In the seven women, increased FDG uptake was due to physiological endometrial uptake (n=2), leiomyoma (n=1), corpus luteum cyst (n=1), physiological ovarian uptake (n=1), urinary leak (n=1), and nonspecific colitis (n=1). In the man, uptake was due to recurrent rectosigmoid adenocarcinoma. None of the 700 patients was found to have metastatic disease in the pelvis. Conclusion: Isolated pelvic hot spots at PET/CT imaging in an oncological population are not common and usually benign; physiological endometrial or ovarian uptake is the single commonest cause.