Pediatric Oncology Education Materials

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.

Distant

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:

Local	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)
CSF	Leptomeningeal involvement in 10 - 45% of cases
Hematogeneous	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

Pediatric OncologyEducation Materials