Renal schwannoma appears on imaging as renal cell carcinoma: a case report

Renal schwannomas are exceedingly rare benign tumors originating from Schwann cells, with fewer than 50 cases reported in the literature. The "ancient" variant refers to long-standing schwannomas that develop degenerative changes, which may mimic the aggressive radiological features of renal cell carcinoma. This diagnostic overlap often leads to preoperative misdiagnosis and can significantly impact surgical decision-making, often resulting in radical rather than nephron-sparing approaches.

A 48-year-old White woman presented with a 3-month history of intermittent left flank discomfort. Imaging demonstrated a 6-cm complex cystic mass at the upper pole and hilum of the left kidney, characterized by thickened, enhancing septations (up to 7.5 mm) and a 13-mm mural nodule, consistent with a Bosniak IV cystic renal mass. No metastases were detected. Owing to the high suspicion of cystic renal cell carcinoma and the complex hilar location, she underwent laparoscopic left radical nephrectomy. Histopathological evaluation revealed a spindle cell neoplasm with Antoni A and B patterns and extensive degenerative changes, including hemorrhage and calcification, confirming a diagnosis of ancient schwannoma. Immunohistochemistry showed strong, diffuse S-100 positivity and SOX10 expression. At 12-month follow-up, the patient remained asymptomatic and disease-free.

Ancient renal schwannomas pose substantial diagnostic challenges as they frequently masquerade as renal malignancies on imaging. While definitive diagnosis currently relies on histopathological analysis, maintaining awareness of this rare entity is important when evaluating complex cystic renal masses. Greater diagnostic awareness may help inform surgical planning and, in selected cases, allow consideration of nephron-sparing approaches.