Pilocytic astrocytoma is a benign brain tumor that grows slowly in the brain or spinal cord. "Pilocytic" means that the tumor is made up of cells that look like fibers when viewed under a microscope. "Astrocytoma" describes the type of tumor that begins in the brain or spinal cord in small, star-shaped cells called astrocytes. The tumor may be in the form of a cyst and rarely spreads into nearby tissues. Symptoms vary depending upon the size and location of the tumor. Most symptoms result from increased pressure on the brain and include headaches, nausea, vomiting, balance problems, and vision abnormalities. This type of tumor is most common in children and young adults and in people with neurofibromatosis type 1 (NF1), Li-Fraumeni syndrome, and tuberous sclerosis. A pilocytic astrocytoma rarely causes death. The exact cause of this tumor is unknown.