medulloblastoma
Meaning of medulloblastoma: The most common cancerous brain tumor of childhood, growing where balance and coordination are controlled.
Definition of medulloblastoma
Medulloblastoma is a fast-growing cancerous tumor that begins in the cerebellum, the part of the brain at the back of the skull that coordinates balance and movement. It is the most common malignant brain tumor in children, and it occurs in adults far less often. Its cells shed easily into the fluid around the brain and can settle further down the spinal cord.
What symptoms does it cause?
The cerebellum sits in a tight compartment at the base of the skull. A tumor growing there presses on the fourth ventricle, the narrow channel that cerebrospinal fluid must pass through on its way out of the brain. When that channel is squeezed, fluid backs up and pressure inside the skull rises, a state called hydrocephalus. That accounts for the usual early signs: headache that is worst on waking, vomiting, and drowsiness. Damage to the cerebellum itself adds unsteadiness, a wide-based clumsy walk and shaky hand movements. In a baby whose skull bones have not yet fused, the head enlarges instead of the pressure building.
How is medulloblastoma classified?
It was long grouped with other small round cell tumors of the nervous system under the label primitive neuroectodermal tumor. Molecular testing has since separated it out as a disease of its own, with four main subgroups defined by the genetic switches driving them.
| Subgroup | Notable feature |
|---|---|
| WNT | Best outlook of the four |
| SHH | Common in infants and in adults |
| Group 3 | Most likely to have spread when found |
| Group 4 | The commonest subgroup |
Why is the spine imaged as well as the head?
Unlike most brain tumors, medulloblastoma travels in cerebrospinal fluid. Loose cells drift with the flow and can implant anywhere along the lining of the brain and spine, seeding deposits well away from the original tumor. Because those deposits change both the stage and the plan, imaging of the whole spinal canal and examination of a sample of spinal fluid form part of the assessment. Treatment usually combines surgery, radiation aimed at the entire brain and spinal canal, and chemotherapy. Radiation is used cautiously in the youngest children because of its effect on the developing brain, and long-term follow-up watches growth, hormone production, hearing and learning.
Used in a sentence
Imaging showed a posterior fossa mass consistent with medulloblastoma, and the spinal canal was screened for further deposits.
Good to know
Medulloblastoma is no longer classified as a primitive neuroectodermal tumor, and its four molecular subgroups carry meaningfully different outlooks.
Word origin
Where “medulloblastoma” comes from
Medulla is Latin for marrow or inner part; blastos is Greek for a sprout or germ cell, and the ending -oma means a swelling or tumor.