Background and Clinical Significance: Spontaneous renal hematoma, also known as Wunderlich syndrome (WS), is a rare disease characterized by the acute onset of spontaneous renal hemorrhage into the subcapsular, perirenal, and/or pararenal spaces without a history of prior trauma. WS can be a life-threatening condition due to hemorrhagic shock; consequently, prompt diagnosis and a therapeutic approach are essential for favorable outcomes. Treatment ranges from conservative management to surgical intervention. The most common etiologies are neoplasms and vascular diseases, but WS can also be observed in patients undergoing hemodialysis. In patients with end-stage renal disease (ESRD), especially those on hemodialysis, acquired cystic kidney disease and renal cell carcinoma are among the primary causes of WS. Although less common, WS can develop in dialysis patients even in the absence of traditional (primary) risk factors. In general, patients with chronic kidney disease (CKD) have a paradoxical hemostatic profile, likely explaining their higher tendency to bleed, so WS can occur without existing predisposing factors. The multifactorial pathogenesis in these patients includes functional platelet abnormalities, intimal arterial fibrosis, chronic inflammation, and oxidative stress associated with ESRD. The use of hemodialysis-related antithrombotic medications could serve as another contributing factor increasing the risk of bleeding. C ase Presentation: We present a case report of a 62-year-old male on chronic dialysis who developed sudden right-sided lumbar pain and hematuria during dialysis without evidence of prior trauma. Imaging revealed a large subcapsular hematoma of the right kidney. Further investigations did not reveal additional risk factors in this instance; however, his routinely used hemodialysis-related antithrombotic medications were potentially a contributing factor. Despite conservative treatment, his condition worsened, and the hematoma enlarged, requiring emergency nephrectomy. Postoperatively, his condition gradually improved. Conclusions: This case highlights the importance of considering WS in hemodialysis patients, even without the presence of traditional risk factors, as well as including WS in the differential diagnosis of acute abdominal pain.

Background and Clinical Significance: Spontaneous renal hematoma, also known as Wunderlich Syndrome (WS) is a rare disease, characterized by the acute onset of spontaneous renal hemorrhage into the subcapsular, perirenal, and/or pararenal spaces, without a history of prior trauma. It can be a life-threatening condition due to hemorrhagic shock, consequently, prompt diagnosis and therapeutic approach are essential for favorable outcomes. Treatment ranges from conservative management to surgical intervention. The most common etiologies are neoplasms, vascular diseases but it can be also observed in patients undergoing hemodialysis, especially those with acquired cystic kidney disease or renal cell carcinoma. However, patients with CKD, on particular those on dialysis, have a paradoxical hemostatic potential with increased rates of bleeding, so WS may occur even without the so-called common risk factors. The multifactorial pathogenesis in these patients includes specific coagulation abnormalities and the impaired architectonics of the renal tissue, as well as the use of antithrombotic agents. Case Presentation: We present a case report of a 62-year-old male on chronic dialysis who developed a sudden right-sided lumbar pain and hematuria during dialysis without evidence of prior trauma. Imaging revealed a large subcapsular hematoma of the right kidney. Despite conservative treatment, his condition worsened and the hematoma enlarged, requiring emergency nephrectomy. Pathology confirmed extensive hemorrhage in a nephrosclerotic kidney. Postoperatively, his condition gradually improved. Conclusions: This case highlights the importance of considering WS in hemodialysis patients, and should be included in differential diagnosis of acute abdominal pain.