Contributed by Marlin Dustin Richardson, MD1; Hilary Somerset, MD2; B.K. Kleinschmidt-DeMasters, MD1,2,3; Allen Waziri, MD1
1 Department of Neurosurgery, University of Colorado Denver, Aurora, CO
2 Department of Pathology, University of Colorado Denver, Aurora, CO
3 Department of Neurology, University of Colorado Denver, Aurora, CO
A 76-year-old man presented to an outside hospital with nausea and vomiting. Further questioning disclosed a two month history of worsening gait instability, dizziness, and frequent falls. His limited past medical history included melanoma of the interscapular region diagnosed six year prior to presentation at an outside hospital.
Magnetic resonance imaging (MRI) of the brain demonstrated a 4.5 centimeter diameter, heterogeneously enhancing, left cerebellar mass with intralesional hemorrhage and possible cystic components (Figure 1). There was significant compression of the fourth ventricle. Imaging of the remainder of the neural axis showed no additional lesions or drop metastases.
The patient underwent a midline suboccipital craniotomy with gross total resection of the tumor. Intraoperatively, a reddish, fleshy tumor was identified. Intraoperative consultation showed a neoplasm with clear-cell morphology. The differential diagnoses included an unusual metastatic melanoma but renal cell carcinoma and (less likely) hemangioblastoma were also considerations.
Post-operative MRI demonstrated no residual enhancing tumor. In addition, comprehensive body imaging of chest, abdomen, and pelvis was negative.
Microscopic examination showed a well-demarcated metastatic tumor composed of lobular nests and groups of cells with focal central necrosis (Figure 2). High power examination revealed large polygonal to round tumor cells with well-delimited cell borders (Figure 3) Some interspersed connective tissue septae contained benign lymphocytes and hemosiderin. The voluminous, pale, eosinophilic cytoplasm was finely vacuolated (Figure 4). The nuclear-to-cytoplasmic ratio was low due to the large amount of bubbly cytoplasm. Nuclei were hyperchromatic and contained irregular chromatin and conspicuous nucleoli (Figure 4). Mitotic activity was relatively modest and the MIB-1 index was 5%. Cytoplasmic melanin pigment was not identified and no typical areas of melanoma were appreciable.
Immunohistochemical markers for renal cell carcinoma (RCC) antigen, epithelial membrane antigen (EMA), CD10 and cytokeratins 7 and 20 were negative. Tumor cells displayed diffuse positive labeling for S100 and Melan-A (Figure 5). Immunohistochemistry for HMB-45 was negative.