Pilocytic Astrocytoma

By MMI board-certified, academically affiliated clinician 
January 16, 2018

Pilocytic astrocytoma (PA) is a slow-growing type of brain tumor. These tumors are often benign or noncancerous. This means that the growth doesn’t spread to other parts of the body. The term “astro” or astrocyte comes from the name of the star-shaped cells from which these tumors develop. Astrocytes are a major type of non-nerve cells in the central nervous system (CNS). The CNS is made up of the brain and spinal cord. Many different types of brain tumors grow from astrocytes. But, PA tumors tend to be among the slowest growing. 

A tumor is an abnormal growth of cells. Doctors who specialize in examining cells under a microscope are called pathologists. They can grade the tumor, on a scale from I to IV, based on how abnormal the cells look and how fast the tumor is likely to grow and invade other tissues. The cells from a grade I tumor look almost normal and grow slowly. A grade IV tumor grows very quickly. 

PA tumors are grade I and tend to grow very slowly. They usually have well-defined borders. They typically do not invade nearby tissues. The cells look almost normal under a microscope. 

PA is a primary CNS tumor. That means that it starts in the brain or spinal cord rather than somewhere else in the body and spreading to the brain. PA most often happens in children and teens, but it can also affect adults. 

Any tumor in the brain may cause problems by pressing against brain tissue. The standard treatment for PA is surgery to remove the tumor, when possible. Once the tumor is removed, the outcome is usually good.

Researchers don’t yet know what causes PA tumors. Doctors also don’t have a clear idea about the risk factors for these tumors. Research has suggested links between some gene defects and these tumors.

The symptoms of PA depend on the tumor’s size and location. The tumor may press on brain tissue and cause symptoms. PA most often grows in the cerebellum, near the back of the brain. The cerebellum controls balance and coordination. PA tumors sometimes affect the optic nerve. A PA tumor may also block the normal flow of cerebrospinal fluid (CSF). CSF normally bathes and cushions the brain and spinal cord. If CSF builds up, you may have symptoms from an increase pressure on the brain (intracranial pressure). This may cause: 

  • Seizures 
  • Headache 
  • Nausea and vomiting 
  • Dizziness and balance problems 
  • Trouble walking 
  • Eye problems 
  • Mental changes

Doctors usually ask about your personal and family medical history, recent symptoms, and past health conditions. You will need a physical exam, and a neurologic exam. For this, your doctor will check your coordination and reflexes. Your doctor may ask you to do simple things like walk, touch your finger to your nose, or hold your hands out. Your doctor might examine your eyes with a light. If your doctor suspects a brain tumor, he or she will want to see medical images of your brain, often with a contrast media. You may need certain tests and procedures, such as:  

  • Magnetic resonance imaging (MRI). MRIs use radio waves, magnets, and a computer to make detailed images of the inside of the body. For this test, you lie still on a table as it passes through a tube-like scanner. If you are not comfortable in small spaces, you may be given a sedative before the test. 
  • Computed tomography (CT) scans. A CT scan uses a series of X-rays and a computer to create detailed images of the inside of the body. During the test, you lie still on a table as it slowly slides through the center of the CT scanner. The scanner directs a beam of X-rays at your body. A CT scan is painless. 
  • Biopsy. In a biopsy, a sample of the tumor tissue is examined for type and grade  

You may first see your primary doctor and then get a referral to a: 

  • Neurologist, a specialist in diagnosing and treating diseases of the brain and spinal cord 
  • Neurosurgeon, a specialist who does brain or spinal cord surgery 
  • Neuro-oncologist, a specialist in brain and spinal cord cancers 

The standard treatment for PA tumors is surgery to remove it. If the tumor is in a spot where it can’t be fully removed, radiation therapy and chemotherapy may be used. 

Sometimes your doctor may want to use radiation therapy after surgery. But, because PA tumors grow very slowly, your doctor may want to “watch” first to see if the tumor comes back. This is because the risks of the radiation therapy may outweigh the risk of the PA growing back. 

You can work with your medical team to talk about the best treatment plan for you. You will likely need ongoing follow-up with your doctor. This may include repeated imaging tests to check whether the tumor comes back. It's very important to keep follow-up appointments so that your medical team can monitor any changes. 

In some cases, the PA tumor may block drainage of the CSF from your brain, causing too much CSF in the brain. If this happens, you may need surgery to put a tube in place to drain excess CSF. After removal of the tumor, this problem goes away.

Rarely, PA tumors may change to a cancerous tumor. Overall, the outcome is good for most people with PA tumors.

  • PA is a non-cancerous type of brain tumor. It arises from the star-shaped astrocyte cells in your brain. These tumors are generally very slow growing.  
  • They most often occur in children and teens but also sometimes happen in adults. Some key points to remember about PA include: 
  • PA tumors are often benign because they typically do not invade nearby tissues. 
  • The usual treatment for PA is to surgically remove the tumor, if possible. 
  • People with these tumors tend to have a good outcome after treatment. 
  • It's very important to follow up with your medical team to continue to monitor any changes after treatment.

Tips to help you get the most from a visit to your healthcare provider:

  • Know the reason for your visit and what you want to happen.
  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
  • Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
  • Ask if your condition can be treated in other ways.
  • Know why a test or procedure is recommended and what the results could mean.
  • Know what to expect if you do not take the medicine or have the test or procedure.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.


January 16, 2018


NCCN Clinical Practice Guidelines in Oncology. National Comprehensive Cancer Network. Version 1.2014. http://www.nccn.org/professionals/physician_gls/pdf/cns.pdf

Reviewed By:  

MMI board-certified, academically affiliated clinician,Turley, Ray, BSN, MSN