A poorly differentiated tumor of the pineal gland most frequently occurring in the first three decades of life consisting of small cells with a scant amount of cytoplasm and often forming pseudorosettes; histologically resembles a medulloblastoma; a type of primitive neuroectodermal tumor. [pineal + G. blastos, germ, + -oma, tumor]
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pin·eo·blas·to·ma (pin″e-o-blas-toґmə) pinealoblastoma.Medical dictionary. 2011.