Urinary ascites secondary to recurrent spontaneous bladder rupture mimicking renal failure: a diagnostic odyssey in a post-radiation patient

Introduction: Urinary ascites secondary to spontaneous rupture of the urinary bladder (SRUB) is a rare clinical entity presenting with non-specific symptoms, which poses a significant diagnostic challenge. A specific presentation involves pseudo-renal failure because of peritoneal reabsorption of urinary solutes. Case description: We present the case of a female in her sixties with recurrent severe abdominal pain and ascites, concomitated with apparent acute kidney injury. Her medical history was significant for Wertheim-Meigs hysterectomy and pelvic radiation for cervical cancer. She underwent multiple hospitalisations with extensive investigations and even exploratory surgeries, driven by misleading CT findings of diffuse bowel wall thickening and gross ascites. The definitive diagnosis was made by extensive review of the patients' medical records and research of similar cases in the literature, as also by paracentesis, revealing an ascites-to-serum creatinine ratio of 3.76. A computed tomography cystogram confirmed an intraperitoneal bladder rupture with contrast extravasation. The patient was successfully managed conservatively with intermittent self-catheterisation. Conclusion: In patients with urogenital comorbidities developing large-volume ascites without preceding trauma, urinary ascites should be considered an important differential diagnosis, typically defined by an ascites-to-serum creatinine ratio of >1. This case explores the diagnostic pitfalls of urinary ascites secondary to SRUB in a patient with late radiation cystitis focusing on the phenomenon of reverse auto peritoneal dialysis and a normal cystatin C level as key diagnostic clues. LEARNING POINTS: Urinary ascites by spontaneous bladder rupture is a rare but critical late complication of pelvic radiation therapy, often misdiagnosed by its non-specific symptoms.Urinary ascites drives the diffusion of urinary solutes back into the systemic circulation, mimicking acute kidney injury by reverse auto peritoneal dialysis.The following constellation of laboratory parameters can be found in uroperitoneum: high serum creatinine but normal serum cystatin C, high serum-ascites albumin gradient and a high ascites-to-serum creatinine ratio.