Spinal Meningeal Melanocytoma with Benign Histology Showing Leptomeningeal Spread: Case Report
A 37-year-old previously healthy man presented with a 2 months history of increasing posterior neck pain and radiating pain to the right upper extremity. Neurological examination showed weakness, numbness and a tingling sensation in the right arm. The remainder of his neurological and physical examination was unremarkable. In particular, examinations of the skin and the fundus of the eye did not reveal any melanotic lesions. Cervial spinal computed tomography (CT) demonstrated a well-defined highly enhanced right-sided intra-spinal soft tissue mass that was homogeneously hyperdense on precontrast CT scan at the C5-C6 level (). Cervial spinal magnetic resonance imaging (MRI) revealed that an intradural extramedullary mass was displacing the spinal cord to the left and was hyperintense on T1-weighted image (T1WI) and hypointense on T2-weighted image (T2WI). Although contrast enhancement of the mass was not evidently revealed by visual assessment due to strong T1 hyperintensity of the mass on unenhanced images, mild diffuse enhancement of the tumor was verified by the quantitative measurement of the signal intensity. The spinal cord was severely displaced and compressed by the mass and was associated with intramedullary signal changes on T2WI, indicating compressive myelopathy (). The patient underwent C5-C6 cervical laminectomy, durotomy and excision of the soft black intradural mass. A subtotal resection was achieved. Some small fragments of the tumor could not be dissected because of adhesion to the spinal cord. Microscopically, the tumor was composed of heavily pigmented spindle cells (). Because a large amounts of melanin pigment obscured cell detail, bleaching of the melanin pigment was performed. Depigmented sections showed a uniform appearance of spindle cells with inconspicuous nucleolus (). Neither necrosis nor mitotic figures were identified, essentially excluding the possibility of a malignant neoplasm. Immunohistochemically, the tumor cells were positive for S-100 protein () and HMB-45, supporting their differentiation toward melanocytes. Ki-67 was expressed in less than 1% of tumor cells, suggesting a low proliferation rate of the tumor. These histopathologic features and immunohistochemical results were consistent with the characteristics of a benign melanocytic neoplasm, thus the tumor was diagnosed as a melanocytoma. The patient's symptoms were postoperatively improved.\nHowever, 2 weeks postoperatively, the patient newly developed lower back pain. Thoracolumbar spinal MR study revealed diffuse leptomeningeal enhancement and intradural small enhancing nodules that were hyperintense on T1WI in the lumbosacral region, indicating leptomeningeal seeding (). Unfortunately, it was uncertain whether the lumbosacral lesions had been presented preoperatively or were newly developed postoperatively because preoperative thoracolumbar evaluation had not been performed. Adjuvant radiotherapy was planned. Whole spinal PET-CT showed only a small focal uptake corresponding to the largest lumbar leptomeningeal nodule on the MRI. There was no uptake in the spinal region including the cervical operative site. Brain MRI was performed to exclude cranial lesion before starting radiotherapy. There was no hydrocephalus nor any other abnormal findings (). The patient underwent postoperative whole spinal radiotherapy. Four weeks postoperatively, the patient presented headache, nausea and vomiting while receiving radiotherapy. Repeated brain MRI revealed newly developed hydrocephalus with subtle leptomeningeal enhancements especially in the base of the brain, indicating obstructive hydrocephalus secondary to leptomeningeal seeding (). A ventriculoperitoneal shunt procedure was performed. Repeated lumbar spinal MRI performed 5 weeks postoperatively revealed an aggravated leptomeningeal mass occupying most of the lumbosacral spinal canal (). Decompressive lumbar laminectomy and partial removal of the leptomeningeal spreading mass were achieved. Microscopically, no evidence of malignant transformation was revealed (). Two weeks after the lumbar spinal operation, a follow-up brain MRI revealed persistent hydrocephalus associated with diffuse enhancing intracranial leptomeningeal masses in the cranial nerves, the brainstem, and the brain (). The disease advanced and the patient expired, months after the initial diagnosis.