Medulloblastoma

Summary

Medulloblastomas are malignant brain tumors that come from primitive neuroectoderm cells. They commonly arise in the cerebellum, and they may occasionally spread to the spinal cord below, in what is known as a “drop metastasis”. Medulloblastomas are usually found in children, and are actually the most common malignant brain tumor in children. Patients affected usually exhibit signs of increased intracranial pressure, like headaches and papilledema, as well as ataxia due to cerebellar dysfunction. A histopathological assessment will reveal a solid, non-cystic appearance on gross pathology , with sheets of small blue cells forming Homer-Wright rosettes under the microscope. These tumors also stain synaptophysin positive.

Key Points

• Medulloblastoma
  • Pathophysiology
    • Malignant tumor arising from primitive neuroectoderm
      • Also known as a primitive neuroectodermal tumor (PNET)
  • Location
    • Commonly arise in the posterior fossa (cerebellum)
      • Classically affect the cerebellar vermis
      • Can cause “drop metastases” to the spinal cord
  • Presentation
    • Most common malignant brain tumor in childhood
    • Signs of increased ICP
      • Headaches
      • Papilledema
    • Ataxia
  • Histology
    • Sheets of small blue cells
      • Poorly differentiated appearance with scant cytoplasm
      • High mitotic index
    • Contains Homer-Wright Rosettes
      • Tumor cells grouped around neuropil (glial and nerve fibers)
    • Solid (non-cystic) appearance
    • Stains Synaptophysin Positive
  • Treatment/Prognosis
    • Mainstay is surgical resection
    • Treated with  radiation and chemotherapy
    • Usually has a poor prognosis