Intraosseous malignant peripheral nerve sheath tumor of the sacrum in a patient with neurofibromatosis type I

Malignant intraosseous peripheral nerve sheath tumor is a very rare malignancy most commonly seen in patients with neurofibromatosis type 1. This tumor almost exclusively occurs in the maxillofacial region, with manifestation of this tumor in other regions of the skeleton infrequently reported. We describe a 23-year-old female with previously undiagnosed neurofibromatosis type 1 presenting with lower extremity weakness, paresthesias, and bowel/bladder symptoms. The patient had an aneurysmal lytic bone lesion centered in the upper sacrum with invasion of the L5 vertebral body. On MRI, the lesion was homogeneously isointense to muscle on T1, heterogeneously hyperintense to muscle on T2, and demonstrated homogeneously avid contrast enhancement. Multiple additional small lesions with similar imaging characteristics were identified in the paraspinal soft tissues. Low grade malignant peripheral nerve sheath tumor of the sacrum was diagnosed on biopsy. The patient was treated with sacral resection and radiation therapy for local disease control.