Mucinous urachal adenocarcinoma: A potential nonfluorodeoxyglucose-avid pitfall on (18)fluorine-fluorodeoxyglucose positron emission tomography/computed tomography

Mucinous adenocarcinoma of the urachal remnant is a nonurothelial malignancy that may be asymptomatic until locally advanced or metastatic. We describe a 37-year-old woman with invasive ductal breast carcinoma who underwent (18)Fluorine-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) computed tomography (CT) demonstrating a non-FDG avid pelvic mass, initially suspected to represent a pedunculated uterine fibroid. Magnetic resonance imaging revealed a mixed solid-cystic mass separate from the uterus, suspicious for urachal neoplasm, confirmed as mucinous adenocarcinoma on histopathology. Urachal tumors may not be FDG-avid and represent a potential pitfall on FDG PET/CT.