How Doctors Diagnosis a Brain Tumor

Using History, Physical Exam, MRI, and Biopsy to Diagnose Brain Tumors

Close-up of a businesswoman suffering from a headache
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Brain tumors even haunt the minds of those who will never develop cancer.  Headaches, tingling, dizziness and other very common symptoms may set off the fear that a deadly malignancy lurks underneath the everyday façade.  How can doctors reassure us, or worse, be confident that a brain tumor is in fact present?

Signs and Symptoms of Brain Tumors

Brain tumors take up space in the skull that should be used by blood, brain, or cerebrospinal fluid (CSF).

Because the skull is a confined space, a tumor often increases intracranial pressure, with telltale signs of blurred vision or headaches that worsen when lying flat. That being said, these are not hard and fast symptoms, as some tumors spread more slowly and do not take up much space at first.

Focal or localized neurological deficits are another indication that something is impacting just one part of the brain, rather than everything at once. Different parts of the brain are responsible for different tasks. For example, the left side of the brain controls the right side of the body.  If both sides of the body are weak, the trouble could be with the muscles or the peripheral nerves — but something that has impacted both sides of the brain is less likely.  If just half of the body is weak, neurologists worry more about the brain and spinal cord.  Similarly, language, personality changes, or other cognitive deficits can indicate a focal brain problem.

MRI to Detect a Brain Tumor

Different kinds of tumors have different appearances on Magnetic Resonance Imaging or MRI. For example, brain metastases tend to be located close to the edge of the brain, since the metastases spread by the bloodstream. The edges of the brain tend to be where the blood vessels are small, where pieces of tumor are more likely to have time to cross the blood-brain barrier.

On the other hand, a type of brain tumor called glioblastoma multiforme tends to be a large tumor that spreads across several different areas of the brain. Another brain tumor called an oligodendroglioma may have bright spots due to calcium deposits within the brain. 

This all being said, the definitive way to know what type of brain tumor is present is to remove a piece of abnormal tissue and look at it under the microscope.

Lumbar Puncture to Detect a Brain Tumor

In addition to neuroimaging, a lumbar puncture can look for abnormal cells that are floating in the cerebrospinal fluid, which is a clear fluid that bathes and surrounds the brain. This can be tricky, however, as there may be only a few free-floating cells, and one cerebrospinal fluid collection may not obtain enough cells for identification.

Biopsy of the Brain to Detect a Brain Tumor

Surgical resection or removal of the brain tumor is clearly a delicate matter.  The surgeons will rely on neuroimaging, like electroencephalography and intraoperative MRI, to help them know exactly where to cut and to stay away from healthy brain tissue.

Most of the time, surgeons plan for both a tumor biopsy and a resection, meaning they may remove as much of the tumor as they can.

In this case, the surgeons can send a piece of brain to be viewed under a microscope by a pathologist while they're still in the operating room. If the pathologist believes the tissue is cancerous, the surgeons can go on and remove as much of the tumor as possible right then and there.

Alternatively, there may be times where the surgeons perform a small biopsy, where there is no plan to remove the tumor at the same time.  This may be the case if the tumor is in a critical location, for example, and extensive surgery would be too dangerous.

More Information Than Just the Type of Brain Tumor

The neuropathologists who look at these cells can do more than just say what type of tumor is present.

The appearance of the tumor can also allow comments on how aggressive the tumor is.  Some stains may be used to determine how sensitive the tumor will likely be to different types of treatments. This information will guide a doctor's recommendations on the best line of care, and may also give a sense of how well the patient will do in the immediate future. 


Miller, A. Neuro-oncology. Continuum: Lifelong Learning in Neurology. 2012, 18:2, 263-501

Ropper AH, Samuels MA. Adams and Victor's Principles of Neurology, 9th ed: The McGraw-Hill Companies, Inc., 2009.