S-100 Negative Intramedullary Melanocytoma – a Case Report and Literature Review

Introduction: Intramedullary melanocytomas, rare benign lesions derived from leptomeningeal melanocytes, are primarily located in the thoracic spine. Since their initial description in 1972, only 26 cases have been documented in the U.S. These tumors, despite their benign classification, can exhibit aggressive behaviors such as local invasion and recurrence post-resection. The diagnosis typically relies on immunohistochemistry, with S-100 protein and melanocytic markers commonly expressed. This report details a rare case of S-100 negative thoracic intradural intramedullary melanocytoma, presenting clinical, imaging, and histopathological insights.

Methods: A comprehensive literature search was conducted through PubMed, Medline, and Scopus, using the query “(Intramedullary) AND (melanocytoma)”. The search encompassed all case reports without publication date restrictions, focusing on English-language studies involving human subjects.

Results: We present a 76-year-old male with a history of lumbar spinal stenosis, paraplegia, and neurogenic bladder who reported burning pain in the thoracic region. MRI revealed a 5.6 cm enhancing mass at T11-T12, causing significant spinal cord effacement. The patient underwent a complete laminectomy and tumor resection from T9 to T12. Preoperative assessments included evoked potentials. The tumor appeared grey and underwent surgical resection. Intraoperative frozen sections suggested ependymoma, but final histopathological analysis confirmed melanocytoma, characterized by pigmented cells and negative S-100, with positive EMA, SOX10, and vimentin markers. Literature review revealed 25 publications, comprising 31 patients, predominantly in the thoracic region. Notably, only one other case of S-100 negative intramedullary melanocytoma has been documented.

Conclusion : This case underscores the diagnostic challenges of intramedullary melanocytomas and emphasizes the necessity of comprehensive histopathological evaluation. Although S-100 positivity is typical, its absence does not exclude the diagnosis. Our findings contribute to the understanding of this rare entity, highlighting the importance of complete surgical resection and ongoing research into atypical presentations.