Extradural malignant melanotic nerve sheath tumor of the lumbosacral spine: a diagnostic and surgical challenge.

Introduction and importance: Malignant melanotic nerve sheath tumor (MMNST) is a rare and potentially aggressive variant of schwannoma that arises from Schwann cells containing melanin. These tumors most frequently occur in the spinal nerve roots and are often misdiagnosed due to their radiological and histopathological similarities with other pigmented lesions such as malignant melanoma or pigmented meningioma. Accurate diagnosis is crucial, as MMNST carries a higher risk of local recurrence and distant metastasis compared to conventional nerve sheath tumors.

Case presentation: We report the case of a 30-year-old male who presented with a 6-month history of progressive left-sided leg pain, lower backache, and paresthesia. Neurological examination revealed decreased perineal sensations and tenderness in the lumbosacral region. MRI of the lumbosacral spine showed an extradural, well-circumscribed, T1 hyperintense lesion with mass effect on the left L5, S1, and S2 nerve roots. The patient underwent surgical resection, and the lesion was found to be encapsulated and pigmented. Histopathology confirmed the diagnosis of MMNST. Immunohistochemistry was positive for S-100 and HMB-45. Postoperative recovery was uneventful, and no recurrence was observed at 6-month follow-up.

Clinical discussion: MMNST poses significant diagnostic and therapeutic challenges. While MRI may suggest a pigmented lesion, definitive diagnosis relies on histopathology and immunohistochemical markers. Given its malignant potential, complete surgical resection with long-term follow-up is the mainstay of management. In this case, the tumor's extradural location and involvement of the sacral nerve roots added to the surgical complexity. Multidisciplinary collaboration was pivotal in planning surgical excision and monitoring for recurrence.

Conclusion: MMNST should be considered in the differential diagnosis of pigmented spinal lesions, especially in young adults with progressive neurological symptoms. Early recognition and complete surgical resection remain essential for optimal outcomes. This case highlights the importance of integrating imaging, histopathology, and immunohistochemistry to ensure accurate diagnosis and guide management.