Background: Renal anastomosing hemangioma (RAH) is an extremely rare benign vascular tumor first described in 2009. Making this diagnosis is fraught with challenges. Radiologically they share features consistent with renal cell carcinomas (RCCs). Their vascular nature poses risks if considering preoperative biopsy and histologically they share characteristics akin to angiosarcomas. The few reports published in the literature suggest presentation with hematuria, flank pain, and polycythemia although the majority are diagnosed at postnephrectomy histologic examination. This case represents the first metachronous RAH in the literature, and is the first RAH presenting with severe hemorrhage. Case Presentation: A 62-year-old woman of Albanian heritage presented to urology with visible hematuria and positive urine cytology. Three years before this presentation, she had undergone an elective radical right-sided nephrectomy for a suspected RCC detected on magnetic resonance imaging, which proved to be an RAH after postoperative histologic examination of the specimen. The patient was investigated with cystoscopy and ureteroscopy for this new hematuria presentation, both of which were unremarkable. Fourteen hours post ureteroscopy, the patient became severely hypotensive and developed acute kidney injury. A CT scan indicated a large left-sided renal subcapsular and retroperitoneal hematoma that was actively bleeding. The patient was hemodynamically unstable and, therefore, required an emergency open left-sided nephrectomy, rendering her anephric and dialysis dependent. Postoperative histologic examination proved that the left kidney also contained an RAH. Conclusion: The anastomosing hemangioma is an important subtype to differentiate from angiosarcoma before and after a nephrectomy. Urologists should carefully consider invasive tests in patients with previously diagnosed vascular lesions as there may be an increased risk of bleeding. Patients with a previously diagnosed anastomosing hemangioma may require surveillance of the contralateral kidney.

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