Transparsinterarticularis approach for resection of a malignant melanotic nerve sheath tumour of the dorsal spine: A case report

Introduction: Malignant melanotic nerve sheath tumours are extremely rare central nervous system neoplasms. Initially termed as Melanotic schwannoma the nomenclature was revised in 2020 WHO classification to malignant melanotic nerve sheath tumour (MMNST). They are rare aggressive peripheral nerve sheath tumours. In spine, they more commonly occur in the lumbosacral region (47.2%), followed by the thoracic (30.5%) and cervical (22.2%) segments. Most common age group affected is between 20-50 years. MMNSTs often tend to metastasize early and have poor prognosis. Surgical excision is the mainstay of treatment followed by radiotherapy and/or chemotherapy. Case report: Here we present the case of a 54-year- old male who presented with gradually progressive lower limb weakness and hypertonia with bowel and bladder involvement. Magnetic resonance study of the spine suggested an intradural extramedullary melanoma at D4 level of spine. The rest of the physical examination and metastatic workup were unremarkable. The patient subsequently underwent tumour excision via trans-parsinterarticularis approach. Histopathological examination was suggestive of malignant melanotic nerve sheath tumour. Following surgery the patient’s lower limb weakness improved significantly. At six-month follow-up patient did not show any signs of recurrence. Conclusion: Malignant melanotic nerve sheath tumours (MMNSTs) are extremely rare highly aggressive lesions that are often misdiagnosed on neuroimaging. When a spinal tumour arising from a nerve root demonstrating the characteristic of T1 hyperintensity and T2 hypointensity, MMNST should always be included in differential diagnosis and metastatic workup, Clinical and radiological evaluation should be done to rule out other associated syndromes. Complete surgical excision followed by vigilant follow-up for early detection of recurrence is recommended.