For example, as pinealomas, medulloblastomas, and ependymomas enlarge - the mass of the tumor can compress nearby ventricles blocking the flow of cerebrospinal fluid which causes swelling, called hydrocephalus.
Now, while medulloblastoma may be the most common malignant tumor, the most common primary pediatric tumor is a type of astrocytoma called a juvenile pilocytic astrocytoma.
Histologically, medulloblastomas often have a feature called Homer-Wright rosettes, which are dense tangles of neurons and neuroglial cells, surrounded by ring-like structures formed by tumors cells.
These patients had a lot more non-T cell stuff, specifically myeloid cells, you know, the immune system's first responders, but they can also be really suppressive in cancer settings.