Case 3 -

Medulloepithelioma Roger E. McLendon Duke University Medical Center Durham, NC

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Clinical History The patient was a 3-year-old white male diagnosed with a posterior fossa brain tumor after presenting with wide based gait, nausea, vomiting, headache and "the room being upside down." A head CT revealed a 4 cm mass in the left lateral cerebellum displacing the 4th ventricle and both the 3rd and lateral ventricles were enlarged. He underwent near total resection on 1/29/93 and pathology revealed the present tumor without invasion of the brain stem. He has subsequently been followed by his local medical doctor. Case 3 - Figure 1 - The tumor is diagnosed by its unique secondary structures, the ribbons and papillae that form an abortive neurotubular epithelium. These structures exhibit a stratified or pseudostratified lining of elongated cells that superficially form a linear, epithelioid arrangement and centrally abut a vascular structure. Cytologically, the tumor cells are devoid of cilia thereby distinguishing them from tumors of ependymal or choroid plexus cells. Case 3 - Figure 2 - The tumor is diagnosed by its unique secondary structures, the ribbons and papillae that form an abortive neurotubular epithelium. These structures exhibit a stratified or pseudostratified lining of elongated cells that superficially form a linear, epithelioid arrangement and centrally abut a vascular structure. Cytologically, the tumor cells are devoid of cilia thereby distinguishing them from tumors of ependymal or choroid plexus cells. Diagnosis Medulloepithelioma Discussion The medulloepithelioma is the most primitive of the malignant embryonal tumors of neuroectodermal origin. It is identical in histologic form to the tumor of the same name arising within the ciliary body of the eye. Within the cranial vault, the tumor most commonly arises in the posterior fossa and is characterized by a profusion of cells with very large nuclei and a modest amount of cytoplasm (Kodachrome 1). Extensive necrosis with the formation of pseudopapillae is common. The tumor is diagnosed by its unique secondary structures, those of ribbons and papillae that form an abortive neurotubular epithelium (Kodachrome 1 and 2). These structures exhibit a stratified or pseudostratified lining of elongated cells that superficially form a linear arrangement and centrally abut a vascular structure. Cytologically, the tumor cells are devoid of cilia thereby distinguishing them from tumors of ependymal or choroid plexus cells. Mitotic figures are numerous and tend to be located along the basal cell layer in the ribbons. Another feature of medulloepitheliomas is divergent differentiation particularly along neuroepithelial lineages. With immunohistochemical staining the tumor may reveal foci of immunoreactivity for either GFAP or synaptophysin within densely cellular regions that are otherwise nondescript by light microscopy. A nodular growth pattern may also be found and these nodules may exhibit either GFAP or synaptophysin immunoreactivity. Others have identified divergent mesenchymal phenotypic markers. References Auer, R.N. and Becker, L.E. (1983) Cerebral medulloepithelioma with bone, cartilage, and striated muscle. Light microscopic and immunohistochemical study. Journal of Neuropathology and Experimental Neurology 42, 256–67. Best, P.V. (1974) Posterior fossa medulloepithelioma. Journal of the Neurological Sciences 22, 511–8. Caccamo, D.V., Herman, M.M. and Rubinstein, L.J. (1989) An immunohistochemical study of the primitive and maturing elements of human cerebral medulloepitheliomas. Acta Neuropathologica 79, 248–54. Jellinger, K. (1972) Cerebral medulloepithelioma. Acta Neuropathologica 22, 95–101. Molloy, P.T., Yachnis, A.T., Rorke, L.B., Dattilo, J.J., Needle, M.N., Millar, W.S., Goldwein, J.W., Sutton, L.N. and Phillips, P.C. (1996) Central nervous system medulloepithelioma: a series of eight cases including two arising in the pons. Journal of Neurosurgery 84, 430–6. Pollak, A. and Friede, R.L. (1977) Fine structure of medulloepithelioma. Journal of Neuropathology and Experimental Neurology 36, 712–25. Scheithauer, B.W. and Rubinstein, L.J. (1979) Cerebral medulloepithelioma. Report of a case with multiple divergent neuroepithelial differentiation. Child's Brain 5, 62–71. Troost, D., Jansen, G.H. and Dingemans, K.P. (1990) Cerebral medulloepithelioma--electron microscopy and immunohistochemistry. Acta Neuropathologica 80, 103–7.