Retroperitoneal biloma—A rare differential diagnosis of perirenal fluid accumulation

Introduction Nontraumatic biliary rupture and retroperitoneal biloma infrequently occur. Here, we report a case of retroperitoneal biloma due to spontaneous left hepatic duct perforation, which was difficult to differentiate from a perirenal abscess. Case presentation A 94‐year‐old female patient was hospitalized with symptoms of fatigue and right back pain that lasted for 5 days. Computed tomography revealed fluid accumulation in the retroperitoneum, and urinary extravasation and right perinephric abscess were suspected. Antimicrobial treatment and drainage with ureteral stents and urethral catheters demonstrated no symptom improvement. Ultrasound‐guided puncture of the abscess revealed the presence of bile. Pigtail catheter drainage improved symptoms and inflammatory response. After diagnosis, endoscopic retrograde cholangiopancreatography revealed bile leakage, and a bile duct stent was inserted. Conclusion Biloma can cause perirenal fluid accumulation, and they should be considered an origin of perirenal fluid accumulation when urinary tract lesions are excluded.