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Patterns of Tumor Spread



  • Medulloblastomas arise most often in the midline cerebellar vermis.
  • Tumor usually grows to fill the 4th ventricle, and commonly involves the brachium pontis and extends onto the ventricular floor (i.e. the brainstem).
  • Medulloblastomas may grow to fill the entire posterior fossa, invading other CNS structures.
  • Unlike ependymomas they do not tend to extend through the foramina of Luschka.


The image below shows a large midline posterior fossa tumor (T) - this is a medulloblastoma.



  • Widespread seeding of the subarachnoid space may occur (risk of this is 10 - 45%).
  • Spinal leptomeningeal disease, appears in about 30% of cases at presentation.
  • Intracranial metastasis are less common.
  • Distant metastases are rare but may occur in bone marrow/bone.


The MR below shows multiple nodules of metastatic disease involving the subarachnoid space in a child's spine. #1 points to a large nodule.


Summary of Patterns of Medulloblastoma Spread:

  • Grows to fill and obstruct the 4th ventricle
  • Commonly involves the brachium pontis
  • Extends onto the floor of the IVth ventricle and may involve brainstem (often after resection of a medulloblastoma, a thin film of tumor remains as resection in this area would be potentially dangerous and result in damage to the brainstem) 


  • Leptomeningeal involvement in 10 - 45% of cases

  • Very uncommon, but metastatic disease can occur in bone
  • Reported to occur in liver, but this is extremely rare


VP Shunt
  • When VP (ventriculo-peritoneal) shunts were in common use, metastatic disease could spread down the shunt to involve the peritoneal cavity



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