Intramedullary epithelioid malignant peripheral nerve sheath tumour arising from sporadic schwannoma in the thoracic spine: first case report and review of the literature.

Background: Intramedullary schwannomas and malignant peripheral nerve sheath tumours (MPNSTs) are extremely rare entities. This report documents the first known case in the literature of an intramedullary spinal MPNST, specifically of epithelioid subtype, to arise from an intramedullary schwannoma. Whilst epithelioid malignant peripheral nerve sheath tumours (EMPNSTs) are less likely overall to arise from a benign peripheral nerve sheath tumour (BPNST) compared to a conventional MPNST, there is a predisposition if the primary tumour is a schwannoma and if the patient does not have neurofibromatosis type 1 (NF1). Case Description: We present the case of a patient with an intradural T11/12 schwannoma containing intramedullary and extramedullary components. Resection of the extramedullary component was performed initially. Three years later, the patient developed significant myelopathy related to the residual intramedullary portion of the antecedent tumour. A redo thoracic laminectomy and debulking of the intramedullary lesion was performed. Histopathology revealed a diagnosis of EMPNST. This represents the first case of an intramedullary spinal MPNST arising from an intramedullary schwannoma, the first report of an intramedullary EMPNST and only the fourth report of an intramedullary spinal MPNST. Conclusions: This rare case highlights a potentially unique relationship between sporadic schwannomas and EMPNST. Despite its rarity, clinical suspicion should be maintained regarding the malignant transformation of an incompletely resected schwannoma, especially in unusual locations such as the intramedullary spine.