In case you just joined us, we’re doing a series on brain tumors (so far we’ve had an overview and a look at astrocytoma). Today we’ll talk about pilocytic astrocytoma, a brain tumor that generally behaves pretty well. Pilocytic astrocytomas (also called grade I out of IV astrocytomas) are pretty unique both in the way they look and in the way they act. They occur mostly in children and young adults, and they are most common in the cerebellum (though they can also occur in the third ventricle, the optic nerves, and the cerebral hemispheres).

Microscopically, the tumor has bipolar cells with long “hairlike” (hence the name “pilocytic” from the Latin pilus, or hair) projections that form a fibrillary mesh. Check out the long, hair-like process in the above smear (it’s not a section!) of a pilocytic astrocytoma. Sometimes the meshwork is loose, and sometimes (even in the same tumor) it’s pretty dense. A weird finding in these tumors is the presence of Rosenthal fibers (or Rosenthal bodies), chunky, red, rod-like structures that contain heat shock proteins and ubiquitin.. Can’t miss them! Sometimes these tumors can be cystic – both grossly and microscopically.

The clinical behavior of this tumor is unusual too – it grows veerrry slowly (some patients live up to 40 years without treatment). It’s generally resectable (except when it occurs in the optic nerves, which is more complicated due to the location). Prognosis is accordingly good: if the tumor is completely resected, the 10 year survival rate is 90%.