Retroperitoneal neurilemmoma is a rare benign tumor originated in the retroperitoneal spinal nerve sheath. Its malignant transformation is extremely rare. Neurilemmoma was firstly described by Verocay and also called Schwann’s tumor (Stout, 1946) because of Schwann’s cellular origin. In recent years, some studies suggest that Schwann’s cells with multiple differentiation potential can form a variety of mesenchymal cells and transform backward to the original neuroepithelial cells. Therefore, Schwann’s cells are not only neurilemmoma cells but also metrocytes of soft tissue tumors. Malignant neurilemmomas usually are transformed from neurofibromas or neurofibromatosis; however, benign neurilemmoma rarely undergoes malignant transformation. Both benign and malignant neurilemmomas are very rare, commonly seen in people aged 20–50 years, with the incidence rate approximately equivalent between men and women.
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