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How to Diagnose Brain Tumors

At Johns Hopkins, the brain tumor team will perform a variety of examinations to diagnosis a brain tumor. Magnetic resonance imaging (MRI) and computed tomography (CT or CAT scan) are the most common types of tests used to diagnose brain tumors. Both MRI and CT scans use computers to create detailed images of the brain. Depending on the patient, the doctor may request any of the following:

A neurological exam

A physician will assess the person’s symptoms by asking about the patient’s personal and family health history. This information combined with the neurological exam provides clues about whether a person might have a brain tumor and where it might be located.

The neurological exam includes checking vision, hearing, strength, sensation, balance, coordination, reflexes and ability to think and remember. For example, the doctor may ask a person to:

  • Follow a moving finger with the person’s eye to check vision
  • Walk heel-to-toe to check coordination

If the doctor thinks a brain tumor is likely, the next step would include a scan of the patient’s brain.


An angiogram is a type of X-ray of the head that shows the brain’s arteries and veins. A contrast dye is injected into the main arteries of the head before the test.

Brain scans

To show abnormalities like a brain tumor, a contrast dye is often used. The dye is injected into a vein in the arm. A brain tumor generally soaks up more dye than normal brain tissue and shows up clearly on the scan; occasionally, a brain tumor does not absorb more dye.

Neuroradiologists perform all brain scans at the Johns Hopkins Comprehensive Brain Tumor Center.

CT scans

CT scans are a type of X-ray that creates a three-dimensional picture of the head by scanning the head from multiple different angles. A computer combines these images into a detailed, cross-sectional view that shows abnormalities in the brain, or tumors.

CT scans can be helpful in diagnosing some types of brain tumors, especially those near or involving bone. They can also show swelling, bleeding, and bone and tissue calcification.

This is often the first scan that will be used, especially in emergency situations.

Diffusion Tensor Imaging (DTI)

DTI of a metastatic brain tumor
DTI of metastatic brain tumor

DTIs measure the flow of water through the white matter tracts of the brain. This provides a snapshot of the brain's structure and can be used to compare changes over time.

Patients can receive a scan called Diffusion Tensor Imaging (DTI). This scan allows the surgeon and treating team to visualize the circuitry (or wiring) of the brain to guide the surgery. In the image below, the green demonstrates wires that connect the front and back of the brain; the red delineates the wires that connect the right and left side of the brain; and finally, the blue shows the wires that connect the brain to the rest of the body. These images can then be loaded into navigation systems that are used in the operating room as a GPS and map for the surgeon.


Functional Magnetic Resonance Imaging (fMRI) scans

fMRI of metastatic brain tumor
fMRI of metastatic brain tumor

FMRI is used to determine the specific location of the brain where a certain function, such as speech or motor function, occurs. During functional resonance imaging of the brain, the patient is asked to perform a specific task, such as recite the Pledge of Allegiance, while the scan is being done. By pinpointing the exact location of the functional center in the brain, physicians can plan surgery or other treatments for a particular disorder of the brain.

Magnetic resonance spectroscopy (MRS) and positron emission tomography (PET) scans can also be helpful in diagnosing primary brain tumors.

Patients can undergo functional MRIs (fMRI) to help delineate a roadmap of important structures (such as areas that control the arms, legs, or speech) prior to surgery. The example shown below demonstrates a tumor near the area for extremity movement. The blue and red areas specify the part of the brain that moves the arms and legs.


brain MRI scanMRI scan of the brain

Magnetic Resonance Imaging (MRI) scans

The best type of imaging to diagnose most types of brain tumors is MRI. These scans use magnetic fields and radio waves, rather than X-rays, and computers to create detailed pictures of the brain.

MRIs show visual “slices” of the brain that can be combined to create a three-dimensional picture of the tumor.

A contrast dye may be used to enhance the scan images.

Magnetic Resonance Spectroscopy (MRS) scans

MRS is another noninvasive procedure used to assess chemical abnormalities in body tissues such as the brain. MRS may be used to assess disorders such as an infection of the brain, stroke, Alzheimer's disease, multiple sclerosis, scarring after radiation, and tumors.

MRS is similar to MRI, except that it measures the function of the brain rather than its structure. It also shows some features of brain tumors that may not be clear on an MRI scan.

Positron Emission Tomography (PET) scans

A PET scan detects changes in cells as they grow. A small amount of radioactive glucose is injected.  Depending on the grade on the tumor, tumor cells absorb a characteristic amount of the radioactive glucose in comparison to normal parts of the brain. A PET scan can help determine how serious a growth in the brain is.

Biopsy (tissue sample analysis)

A biopsy is a surgical procedure to remove a small sample of the tumor for examination under a microscope. Most of the time, the biopsy is done during surgery to remove the brain tumor (called an open biopsy).

A biopsy can also be performed as a separate procedure called a needle biopsy, if:

  • The tumor cannot be removed without damaging critical parts of the brain or
  • The patient is not well enough for open surgery.

In a needle biopsy, the neurosurgeon drills a small hole in the skull and inserts a narrow, hollow needle into the tumor. The neurosurgeon removes a sample of the tumor through the core of the needle.

A stereotactic biopsy is one type of needle biopsy that uses a computer and a three-dimensional scanning device to find the tumor. Learn more about biopsies.

Other tests used to diagnose brain tumors

Other tests may be used to diagnose specific types of brain tumors. For example:

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