35-year-old woman with progressive bilateral leg weakness

A 35-year-old woman presented with one month's history of progressive bilateral leg weakness and altered sensation. There had been no pain. She had noted urinary frequency and constipation in the previous two weeks. On examination, the patient had diffuse lower extremity weakness (2-3/5), with a T6 sensory level to pain and temperature sensation. MRI demonstrated a T4-5 intradural mass ventral to the spinal cord, with an enhancing dural tail, consistent with meningioma. At surgery an intradural, extramedullary, firm, black neoplasm was encountered, which invaded the ventral dura and elevated and distorted the spinal cord. The mass was removed, leaving only microscopic invasion of the ventral dura. There was no bone invasion. Serial sections revealed a homogeneous black tumor without necrosis. H&E stained sections showed an occasionally fascicular tumor of melanocytes and small round blue tumor spindle cells with melanin pigmentation and 1-2 mitotic figures per 10 high-powered fields. The nuclei are generally oval-shaped and elongated, with prominent nucleoli. Necrosis, hemorrhage, and nuclear and cellular pleomorphism are not present and mitotic figures are rare. Immunohistochemical staining was positive for S-100 and HMB-45. MIB-1 labeling averaged 1-2%. A diagnosis of primary meningeal melanocytic tumor was made. Primary meningeal melanocytic tumors (PMMTs) are rare; fewer than 100 cases have been described. PMMTs of the CNS consist of a spectrum of tumors ranging from well-differentiated melanocytoma to its overtly malignant counterpart, melanoma. Intermediate grade melanocytomas (IMGs) are the least common variant, comprising about 10% of PMMTs reported. IGMS occur in the spinal leptomeninges and intracranially in approximately equal proportions. IGMs are more cellular than the well-differentiated variant, with 1-3 mitotic figures per 10 HPFs and MIB-1 labeling of <6%. By contrast, melanomas contain more mitotic figures (3-15 per 10 HPF) and MIB-1 labeling rates up to 15%. Once metastasis, including drop metastasis from pigmented medulloblastomas, have been excluded, the differential includes pigmented meningiomas and schwannomas (solitary or as part of Carney complex), as well as other pigmented CNS tumors such as ependymoma and pineoblastoma and systemic diseases such as lymphoma . . . For primary CNS melanocytic neoplasms, complete tumor resection is preferred, as it leads to cure of well-differentiated and intermediate-grade melanocytomas and most melanomas. Radiotherapy is recommended for incomplete resection of IMGs and melanomas; the recurrence potential of low-grade melanocytomas is less clear and watchful waiting may be employed, since recurrent tumors may be treated surgically prior to radiation. Two months after surgery, the patient had normal sensation and strength. She was given focused radiotherapy to the region of the ventral thecal sac to 40 cGy. At one year following surgery, the patient's neurological examination is normal and she remains free of residual disease by MR examination.