Perineurial Malignant Peripheral Nerve Sheath Tumor of the Cauda Equina: Diagnostic Challenge

Malignant peripheral nerve sheath tumors (MPNSTs) are rare sarcomas with an extremely rare perineurial subtype. Herein, we present a case of a perineurial MPNST in the cauda equina. Clinically and radiologically, a mass extending from within the spinal canal at the L5 level to outside the intervertebral foramen was identified, raising suspicion of a neurogenic tumor as the primary diagnosis. Computed tomography-guided biopsy suggested an intermediate- to low-grade malignancy; however, a definitive diagnosis could not be established. Two years later, worsening neurological symptoms prompted further imaging, which revealed significant tumor growth and bone invasion. Open biopsy was performed to obtain a definitive diagnosis of perineurial MPNST. MPNSTs lack distinctive imaging features and are generally diagnosed based on a combination of radiological and histopathological findings. Although MPNSTs have a poor prognosis, the perineurial subtype is considered to have a relatively favorable outcome. Given these factors, early diagnosis followed by surgical resection or radiation therapy is recommended.