[Retroperitoneal malignant peripheral nerve sheath tumor (MPNST) in a patient with neurofibromatosis I: a case report].

A 64-year-old man who was diagnosed with type I neurofibromatosis was referred to our hospital with a pelvic mass incidentally found by ultrasonography. When examined by CT and MRI, the mass in the pelvis was 5 x 3 x 2 cm. In addition, another mass was found close to the obturator nerve at the S1-2 level. Transrectal biopsy was carried out, and a diagnosis of neurofibroma suspicious for low grade malignancy was made. We performed surgical resection of both of the tumors. The resected tumor was pathologically diagnosed as retroperitoneal malignant peripheral nerve sheath tumor (MPNST). We report our case and review the literature of MPNST detected in type I neurofibromatosis.