Tests That Help Evaluate a Brain Tumor
Your doctor will order more tests if he or she thinks you have a brain tumor. Here are some of the tests that might be done:
Magnetic resonance imaging (MRI)
An MRI scanner uses magnets and strong radio waves to make pictures of the brain. MRIs are very useful in diagnosing brain tumors because they allow your doctor to "see through" your skull. This results in clearer pictures of the brain. A technician might inject a special dye into your vein to make it easier to see the difference between a tumor and normal brain tissue. An MRI can show slices of the brain from many different angles. It can show smaller details better than other scans. An MRI is especially helpful in finding cancer in the back part of the brain called the posterior fossa. It is also better at finding cancer within the spinal cord.
Computed tomography (CT) scan
A CT scan is a type of X-ray that provides detailed pictures of the brain. Many images of the brain are taken as the X-ray scanner moves around your head. A computer combines these many images into a useful picture. Sometimes a technician injects a special dye into a vein before the CT scan to enhance the difference between normal and abnormal tissue. CT scans can also show problems that require immediate attention, such as:
Hydrocephalus, which is too much fluid in the brain's ventricles
Edema, which is swelling
A special form of CT scan, known as CT angiography, may be used to look at the blood vessels around a tumor to help plan surgery.
Positron emission tomography (PET) scan
In a PET scan, a technician injects a small amount of a radioactive substance (usually glucose, a type of sugar) into your vein. Fast-growing tissue, such as a tumor, absorbs this substance and can be seen by using a special type of scanner. The radioactive material used in this test is not dangerous. It will leave your body in about six hours. PET scans can help your doctor tell the difference between an actively growing tumor and damage from radiation therapy or a scar from surgery -- tumors light up while damaged tissue does not.
Magnetic resonance spectroscopy (MRS)
An MRS scan can determine the metabolites inside the tumor. Sometimes, this test is used to determine whether a mass is an active tumor or a mass of radiation damage (necrosis).
An angiogram may also be called arteriogram or venogram, depending on which type of blood vessel is accessed. It's a series of X-rays taken after a technician injects a special dye into one of your blood vessels. A technician also inserts a catheter into one of your large blood vessels, usually in your groin, and then positions it with the help of an X-ray. After injection, the dye flows through the blood vessels in your brain and can be seen on X-rays. These X-rays show the tumor and the blood vessels that lead to it, which helps doctors plan surgery.
This test is used less often than in the past. CT angiography and magnetic resonance (MR) angiography are now used more often to look at blood vessels in the brain.
Magnetic resonance angiography (MRA)
This is a special type of MRI. An MRA is a new, less invasive alternative to an angiogram. But certain types of cancer cannot be seen with this technique.
A myelogram is an X-ray of the spine. A technician injects special dye into your cerebrospinal fluid in the spine to help make tumors more visible. This test is rarely done because MRIs offer more information without injecting dye into the spine.
Certain types of tumors can leave calcium deposits. A skull X-ray is very good at seeing these. Skull X-rays will also show changes to the structure of the skull caused by tumors.
You may need formal testing of your vision or hearing. Your doctor may want to do an electroencephalogram, which checks your brain waves, to rule out invisible seizures.
If these tests suggest that a tumor might be present, a neurosurgeon will probably take a biopsy of the tumor. In most cases, this is the only way to know for sure if a tumor is benign or malignant, although sometimes doctors can get enough information to make a diagnosis from the imaging tests alone.
For a brain tumor biopsy, a doctor takes out as much of the tumor as possible through a bone "window" made in your skull. A pathologist examines this sample under a microscope to see if it is cancer.
Another type of biopsy is the stereotactic biopsy. For this biopsy, the neurosurgeon removes a small piece of the tumor with a needle. The needle is carefully guided and placed in the tumor with the help of an imaging test, such as an MRI or CT scan.
Sometimes, the doctor will test the biopsy tissue to see whether certain chemotherapy drugs will work against your tumor.
If you have questions about these tests, be certain to ask your doctor before agreeing to have them performed. All of your concerns should be addressed before the procedure begins.