Contributed by Lasse Dührsen, MD1; Jakob Matschke, MD2 and Manfred Westphal, MD1
1Department of Neurosurgery, University Medical Center, Hamburg-Eppendorf 2Institute of Neuropathology, University Medical Center, Hamburg-Eppendorf, Germany
A 55-year-old woman presented with headaches and dizziness for one and a half years. An initial lumbar puncture and MRI showed no relevant results. In the meantime, she experienced intermittent nausea and vomiting with significant weight loss. Shortly before she was referred to our institution she had for the first time a generalized seizure. A MRI scan now showed FLAIR-signal intense arachnoidea and partial diffuse contrast enhancement in the left central sulcus and sylvian fissures bilaterally as well as cerebral and spinal leptomeningeal enhancement (Figs. 1 and 2). There were no parenchymal lesions. A biopsy of one of the contrast enhancing parts of arachnoidea was planned. Unexpectedly, after opening the dura mater, it was noted that the cerebral surface was covered by densely pigmented black tissue. Three cortical biopsies were taken.
Intraoperative evaluation showed a predominantly leptomeningeal tumor consisting of brownish pigmented atypical cells with moderate pleomorphism (Fig. 3). Examination of the complete excision showed arachnoidea with diffuse infiltration of moderately pleomorphic spindle-shaped or epithelioid cells with eosinophilic cytoplasm and variable pigmentation (Figs. 4, 5 and 6). Nuclei were relatively uniform with mostly round or bean-shaped forms and nucleoli varied from small to prominent (Fig. 7). Mitotic Figures and necrosis were absent and there was no invasion of the brain parenchyma or Virchow-Robin´s spaces. Immunohistochemistry of the tumor cells showed strong positivity for Melan-A (Fig. 8), S100 and HMB45 (not shown). Proliferative potential appeared very low with a Ki67 labeling index of about 1% (not shown). Further molecular studies for MAP kinase-activating mutations in the B-RAF gene revealed no abnormalities (no V600E / V600K-mutation). What is your diagnosis?