RESUMEN
Retroperitoneal Schwannoma, or Neurilemmoma, is a rare tumor that originates in the neural sheath from Schwann cells and accounts for only a small percentage of retroperitoneal tumors. Presentation is typically varied and non-specific, ranging from abdominal pain, abdominal mass or an incidental finding, and the diagnosis is quite often difficult, being confirmed by pathological study afterwards. We report a case of benign retroperitoneal Schwannoma which was incidentally noticed by the patient himself as an abdominal mass. Preoperative imaging studies were not helpful for reaching correct diagnosis. Surgical exploration and complete excision of tumor was successful. The histological diagnosis of the tumor was reported as benign Ancient Schwannoma. Postoperative period was uneventful and the patient was discharged with a partial femoral nerve injury characterized by mild antero-lateral thigh and leg anesthesia, and quadriceps muscle palsy: Medical Research Council Rating Score [MRC] - grade 2 muscle power. At ten weeks, his quadriceps weakness improved to MRC grade 3, and the anesthesia, although still present, is slightly improved