Majority of pilocytic astrocytomas arise in the posterior fossa in children; however, they may also occasionally involve cerebral hemispheres or spinal cord and are sometimes seen in adults. They are considered benign (WHO Grade 1) and are slow-growing tumors. Patients with neurofibromatosis 1 are predisposed to this tumor, especially involving the optic nerve/chiasm. The image is higher magnification of the previous image showing biphasic appearance consisting of microcystic foci and more cellular areas. The tumor cells are usually spindle shaped and have long, hair-like (piloid) processes. The cellular areas resemble fibrillary astrocytomas.