Medulloblastoma

: A type of virulent brain tumor that occurs most frequently in children. Medulloblastomas originate in residual embryonic nerve cells that begin to proliferate. Treatment is by radiation, but is only rarely successful.

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`A tumor consisting of neoplastic cells that resemble the undifferentiated cells of the primitive medullary tube; medulloblastomas are usually located in the vermis of the cerebellum, and may be implanted discretely or coalescently on the surfaces of the cerebellum, brainstem, and spinal cord; they comprise approximately 3% of all intracranial neoplasms, and occur most frequently in children; the neoplastic cells are compactly arranged, rounded or ovoid, with hyperchromatic nuclei and relatively scant cytoplasm, and lie in small and poorly defined groups, or, occasionally, in a pseudorosette pattern (Homer-Wright rosette). A type of primitive neuroectodermal tumor.

- desmoplastic m. subtype of m. with a biphasic pattern of compact sheets of undifferentiated cells alternating with islands of more loosely cohesive cells, generally occurs in adolescence and young adults and has a better prognosis than the usual m..

- melanotic m. a rare variant of m. in which melanin-pigmented cells are present.

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me·dul·lo·blas·to·ma mə-.dəl-ō-.blas-'tō-mə n, pl -to·mas also -to·ma·ta -'tō-mət-ə a malignant tumor of the central nervous system arising in the cerebellum esp. in children

me·dul·lo·blas·to·ma·tous -'tō-mət-əs adj

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n.

a malignant brain tumour (see cerebral tumour) that occurs during childhood. It is derived from cells that have the apparent potential to mature into neurones and develops in the cerebellum, the part of the brain that is predominantly involved in the control of balance. The flow of cerebrospinal fluid (CSF) may become obstructed, causing hydrocephalus. Symptoms include headaches, dizziness, and unsteadiness. Treatment involves surgery to remove most of the tumour and restore CSF flow, followed by radiotherapy directed using stereotactic localization. Medullo-blastoma is the second most common form of cancer of childhood (after leukaemia); recent advances have improved the survival rate so that 40% of affected children live for more than five years.

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me·dul·lo·blas·to·ma (mə-dul″o-blas-toґmə) a malignant, highly radiosensitive cerebellar tumor composed of undifferentiated neuroglial cells and usually considered a type of primitive neuroectodermal tumor. Most medulloblastomas occur in children and arise in or adjacent to the roof of the fourth ventricle.