How Pilocytic Astrocytoma Is Diagnosed

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Pilocytic astrocytoma (PA) is a slow-growing tumor of the central nervous system most commonly found in children and young adults. It can be diagnosed using imaging tests that view the structure of the brain or spinal cord.

Generally, before these tests are ordered, a physical examination is done to determine whether there are neurological changes that suggest a brain tumor. The diagnosis of PA can involve magnetic resonance imaging (MRI) and a computed tomography (CT) scan, and a biopsy (removing tissue for further testing in a lab).

This article will review how PA is diagnosed.

Doctor preparing child for MRI scan

ER Productions Limited/Getty Images


PA is typically located inside the skull, so there are generally no physical changes that you would be able to detect on your own unless your child is an infant and the size of their head grows visibly larger. However, there are a few symptoms of PA that you should be aware of.

In children, PA can present with:

  • Vision changes
  • Coordination and balance issues
  • A headache that awakens a child from sleep
  • Not reaching age-appropriate developmental milestones
  • Behavioral changes (for example, a loud child may become quiet and vice versa)
  • Turning their head in order to see something, as opposed to moving their eyes
  • Vomiting, often projectile

While headaches can be a sign of a brain tumor, they—in the absence of other symptoms—are rarely a sole indicator of PA.

Physical Examination

If you suspect your child has a brain tumor, your healthcare provider will ask about your child's health history and recent symptoms. They will do a physical exam and a neurological exam. For this, the provider will check coordination and reflexes. They may ask your child to do simple things like walk, touch their finger to their nose, or hold their hands out. They might use a light to examine their eyes.


Imaging can confirm the presence of a tumor, assess its size and location within the brain, and detect characteristics that help to differentiate one type of tumor from another. 

The most common imaging tests for brain tumors are MRIs and CT scans.

  • MRI: MRIs use radio waves, magnets, and a computer to make detailed images of the inside of the body. For this test, the patient lies still on a narrow table as it passes through a long, tube-like scanner. MRI is the best test to look for tumors in the central nervous system (brain and spinal cord).

For young kids who are likely to have difficulty staying still for the test, sedation medications are usually given through an intravenous (IV, through a vein) line to help them stay asleep. Sedation is also helpful if a child is claustrophobic. 

  • CT scan: A CT scan uses a series of X-rays and a computer to create detailed images of the inside of the body.

These tests are usually done with injected contrast material, which is fluid that surrounds solid areas, such as brain tumors, to better define their edges. 

Labs and Tests

A biopsy involves removing a small piece of tissue to be tested to determine what type of tumor it is and how fast it is growing. But often, PA can be diagnosed based on how it looks on imaging tests.

In a biopsy for PA, a surgeon makes a small hole in the skull and inserts a hollow needle into the brain. A syringe is then used to extract a tiny piece of the tumor. A biopsy might also be done as part of surgery to remove the tumor.

There is a risk of bleeding or swelling in the brain after the procedure, and your healthcare team will closely monitor your child for neurological changes after their biopsy. 

In some cases, a biopsy is not carried out due to the location of the tumor (for example, tumors located in the optic pathway or the brain stem).

Differential Diagnosis

A tumor in the brain can cause symptoms that are similar to other conditions. During the diagnostic process, your healthcare provider will rule out other conditions that may be to blame for your child's symptoms, including:

  • Brain abscess: An abscess is an enclosed area of infection. These infections tend to be rare, but they can be mistaken for brain tumors due to their symptoms and appearance on imaging tests.
  • Encephalitis: This is a condition characterized by inflammation of the brain that can be caused by an infection or an autoimmune disease. Encephalitis causes a variety of symptoms depending on the region of the brain that is affected. 
  • Multiple sclerosis (MS): MS is uncommon in children. Problems with memory and thinking are some symptoms of childhood MS, as are problems with movement, such as poor coordination and tremor.

Of course, the symptoms of PA can also be caused by conditions that are less severe. Balance issues may be due to a middle ear infection. Projectile vomiting could simply be the result of a virus, and an eye test may clear up any questions over vision issues.


Most tests for pilocytic astrocytoma are minimally invasive and usually a diagnosis can be made without a biopsy being taken. Your healthcare provider will perform a physical exam and a neurological exam before ordering further tests, which could include an MRI or CT scan.

A Word From Verywell

If symptoms of PA are present, it is likely that your child will need to have a series of tests to rule out a brain or spinal cord tumor. If your child is claustrophobic or unable to lie still for imaging scans, they may be given sedation to make the procedure easier.

In some cases, a biopsy needs to be taken to determine if a cancer is present, but your child will be closely monitored afterward for signs of complications.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. American Cancer Society. Tests for brain and spinal cord tumors in adults. Updated May 5, 2020.

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