Anastomosing hemangioma masquerading as renal cell carcinoma in a transplanted kidney: a case report.

Anastomosing hemangioma (AH) is an exceptionally rare benign vascular neoplasm that can closely mimic renal cell carcinoma (RCC) on radiologic and histopathologic evaluation. We report a 63-year-old male kidney transplant recipient who developed a small enhancing renal mass during pretransplant assessment for a second kidney transplantation. The patient had received a deceased donor kidney transplantation in April 1994 and resumed maintenance hemodialysis in April 2025 due to chronic allograft failure. During evaluation for a planned living donor kidney transplantation from his son, abdominal contrast-enhanced computed tomography revealed a 1.4 cm well-circumscribed enhancing mass in the upper pole of the transplanted kidney, highly suspicious for RCC. Magnetic resonance imaging demonstrated a T2 hyperintense lesion with heterogeneous and delayed enhancement, and positron emission tomography-computed tomography showed no hypermetabolic uptake or metastasis. Transplant nephrectomy was performed to exclude malignancy. Histopathologic examination revealed anastomosing capillary-sized vascular channels lined by bland endothelial cells without atypia, consistent with AH. Immunohistochemical staining was positive for CD34 and ERG, confirming endothelial differentiation. This case emphasizes the diagnostic challenge of distinguishing AH from RCC in transplant recipients and highlights the importance of accurate pathologic diagnosis to prevent unnecessary delay in subsequent kidney transplantation.