Epithelial differentiation in medulloblastoma: Comparison with other embryonal tumors of neuroectodermal origin

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Abstract
Three cases of medulloblastoma characterized by epithelial differentiation are described in patients 6‐months‐, 1‐month‐ and 8‐years‐old. Histologically, tumors from the two infant patients showed a perivascular arrangement without apparent radiated cytoplasmic processes from the vessels. Tumor cells displayed round and/or pleomorphic vesicular nuclei and a more abundant eosinophilic cytoplasm than that found in classic medulloblastoma. Neither Homer–Wright rosettes nor ependymal or ependymoblastic rosettes were noted in these tumors. The tumor in the 8‐year‐old patient exhibited a classic medulloblastoma component intermingled with abundant eosinophilic cytoplasm forming a tubular structure. Immunohistochemically, tumor cells in all cases were positive for cytokeratin, synaptophysin, and vimentin. In the third case involving the 8‐year‐old patient, epithelial tumor cells were positive for cytokeratin, whereas classic medulloblastoma components were negative for cytokeratin. Positive staining for melanoma‐specific antigen was seen only in the third case, where strong reactivity of tumor cells formed a tubulus. However, the classic medulloblastoma component was negative for melanoma‐specific antigen. Ultrastructurally, basal laminae were observed around tumor cells in the 6‐month‐old patient. These morphological and immunohistochemical features suggest that medulloblastoma with epithelial differentiation is a rare but distinct variant of medulloblastoma, and that some of these tumors should show differentiation in ocular pigment epithelium.