A Multifactorial Case of Retroperitoneal Fibrosis in a Post-radiation Bladder Cancer Patient: Diagnostic and Therapeutic Challenges.

Retroperitoneal fibrosis (RPF) is an uncommon fibroinflammatory condition characterized by the development of dense fibrotic tissue in the retroperitoneum, often encasing nearby structures such as the ureters, gastrointestinal tract, and blood vessels. It can lead to progressive obstruction of the urinary and gastrointestinal tracts, with clinical manifestations varying depending on the extent and location of involvement. We present a diagnostically challenging case of secondary RPF, most likely triggered by post-radiation changes and autoimmune mechanisms, in a 44-year-old male with a history of high-grade muscle-invasive urothelial carcinoma of the bladder with squamous differentiation, treated with chemotherapy and pelvic radiotherapy. The patient presented with progressive jaundice, abdominal pain, vomiting, and weight loss. Imaging studies, including computed tomography (CT), magnetic resonance imaging (MRI) of the abdomen and pelvis, and magnetic resonance cholangiopancreatography (MRCP), revealed extensive RPF with bilateral ureteric involvement, common bile duct stricture, pyloric narrowing, and colonic stenosis. Laboratory results showed elevated inflammatory markers and a positive antinuclear antibody (ANA) titer. Endoscopic interventions were unsuccessful due to pyloric obstruction. The patient ultimately required bilateral ureteric stenting, percutaneous biliary drainage, and corticosteroid therapy, which led to clinical improvement. The coexistence of post-radiation fibrosis, positive ANA titer (1:160), and previous malignancy-related changes was considered a contributory factor. This case highlights the importance of multidisciplinary management and early intervention in complex presentations of RPF involving oncologic and autoimmune factors.