Spontaneous Renal Hemorrhage Secondary to Acute Pyelonephritis: An Unusual Presentation of Wunderlich Syndrome.

Wunderlich syndrome (WS) is a critical urological emergency defined by spontaneous, non-traumatic renal hemorrhage into the subcapsular and perirenal spaces. While typically associated with renal neoplasms like angiomyolipoma or renal cell carcinoma, this report describes an uncommon presentation of WS secondary to acute pyelonephritis. This case highlights the diagnostic challenge of differentiating infectious etiologies from ruptured malignancies in the acute setting. A 50-year-old female patient with a history of long-standing rheumatoid arthritis presented with sudden-onset, severe left lumbar pain, nausea, and vomiting. Physical examination revealed a palpable left flank mass and tenderness. Laboratory studies were significant for neutrophilic leukocytosis (14,010 µL; 89% neutrophils) and abundant bacteriuria. An abdominal CT scan demonstrated a large (10 x 8.5 x 13.5 cm) hyperdense posterolateral collection within the left kidney with loss of normal renal morphology. Due to active hemorrhage and the intraoperative identification of multiple suspicious parenchymal nodules, an emergency total left nephrectomy was performed. Surprisingly, histopathological evaluation revealed no evidence of neoplasia, confirming a diagnosis of acute pyelonephritis with microabscess formation and associated subcapsular hematomas. The patient was stabilized postoperatively with blood transfusion and discharged in stable condition. Although WS is predominantly neoplasic in origin, acute infectious processes can precipitate catastrophic renal hemorrhage. This case underscores that emergency nephrectomy remains a justified, life-saving intervention when hemodynamic stability is compromised, or malignancy cannot be excluded, even in the presence of purely infectious triggers.