Herniated Bladder Diverticulum Through the Obturator Foramen Mimicking Pelvic Lymph Node on FDG-PET: A Case of Avoided Complication During CT-Guided Biopsy.

Fludeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) is commonly used in cancer staging, but urinary tract activity and anatomical variations can resemble lymph node disease, leading to unnecessary treatments and potentially harmful procedures. Here, we present the case of a patient referred to Interventional Radiology for a CT-guided biopsy of a suspicious pelvic lymph node with FDG uptake on outside PET/CT. The lesion was located between the pectineus and obturator muscles in the left pelvis. During needle insertion, the changing appearance of the lesion prompted the procedure to be paused for further review of available imaging and careful examination. Imaging re-evaluation revealed the target to be a small bladder diverticulum with a long, narrow neck herniating through the obturator foramen, filled with radiotracer-laden urine. The procedure was aborted, and the biopsy was deferred, avoiding potential complications such as bladder perforation or infection. This experience highlights the importance of thorough multimodal correlation and intraprocedural vigilance to identify benign mimics of nodal disease and ensure patient safety.