Diagnosis

A neurological exam is usually the first test given when a patient complains of symptoms that suggest a brain tumor. The exam includes checking eye movements, hearing, sensation, muscle movement, sense of smell, and balance and coordination. The doctor will also test mental state and memory.

Imaging Techniques

X-rays of the skull were once standard diagnostic tools but are now performed only when more advanced procedures are not available. Advanced imaging techniques have dramatically improved the diagnosis of brain tumors in recent years.

Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) is the gold standard for diagnosing a brain tumor. It does not use radiation and provides pictures from various angles that can enable doctors to construct a three-dimensional image of the tumor. It gives a clear picture of tumors near bones, smaller tumors, brainstem tumors, and low-grade tumors. MRI is also useful during surgery to show tumor bulk, for accurately mapping the brain and for detecting response to therapy.

An MRI (magnetic resonance imaging) of the brain creates a detailed image of the complex structures in the brain. An MRI creates a three-dimensional picture of the brain, which allows doctors to more precisely locate problems such as tumors or aneurysms.

A variant called magnetic resonance spectroscopy (MRS) is capable of providing information on the activity of the brain using magnetic resonance imaging. MRS is proving to be accurate for distinguishing dead (necrotic) tissue caused by previous radiation treatments from recurring tumor cells in the brain, a difficult diagnostic issue.

Computed Tomography. Computed tomography (CT) uses a sophisticated x-ray machine and a computer to create a detailed picture of the body's tissues and structures. It is not as accurate as an MRI and does not detect about half of low-grade gliomas. It is useful in certain situations, however. Often, doctors will inject the patient with an iodine dye, called contrast material, to make it easier to see abnormal tissues. A CT scan helps locate the tumor and can sometimes help determine its type. It can also help detect swelling, bleeding, and associated conditions. In addition, computed tomography is used to check the effectiveness of treatments and watch for tumor recurrence.

Click the icon to see an image of a CT scan of the brain.

Positron Emission Tomography. Positron emission tomography (PET) provides a picture of the brain's activity rather than its structure by tracking substances that have been labeled with a radioactive tracer. As with magnetic resonance spectroscopy (MRS), it is also able to distinguish between recurrent tumor cells from dead cells or scar tissue, although MRS is more widely available. PET is not routinely used for diagnosis, but it may supplement MRIs to help determine tumor grade after a diagnosis. Data from PET may also help improve the accuracy of newer radiosurgery techniques.

Other Imaging Techniques. Numerous other advanced imaging techniques may be used for specific purposes, if available or under investigation.

• Single photon emission tomography (SPECT) is similar to PET but is not as effective in distinguishing tumor cells from destroyed tissue after treatments.
• Magnetoencephalography (MEG) scans measure the magnetic fields created by nerve cells as they produce electrical currents.
• Cerebral angiography involves x-rays of blood vessels in the brain. A long, thin tube (catheter) is threaded through blood vessels from a distant site to the brain, and a radiopaque substance (a substance that is impenetrable to x-rays) is injected through it. The role of angiography in glioma is usually limited to planning surgical removal of a tumor suspected of having a large blood supply.
• Radionuclide brain scintigraphy uses a radioactive substance that is administered and absorbed by capillaries in the tumor, which are then viewed using imaging techniques.
• Digital holography, a new technique that provides full three-dimensional mapping, is under investigation.

Lumbar Puncture (Spinal Tap)

A lumbar puncture is used to obtain a sample of spinal fluid, which is examined for the presence of tumor cells. A CT scan or MRI should generally be performed before a lumbar procedure to be sure that the procedure will be safe.

Click the icon to see an image of a lumbar puncture.

Biopsy

A biopsy is a surgical procedure in which a small sample of tissue is taken from the suspected tumor and examined under a microscope for malignancy. The results of the biopsy also provide information on the cancer cell type.

In some cases, such as brain stem gliomas, a biopsy might be too hazardous because removing any healthy tissue from this area can affect vital functions. In such cases, diagnosis must rely on less invasive and possibly less accurate measures. Of promise is the stereotactic technique (also called stereotaxy), which uses computers to provide three-dimensional views of very small areas. This may allow precise biopsies of cancer cells without affecting healthy brain tissue. Expertise in this technique is extremely important, however, and the technique is not widely available.

Determining a Prognosis

The survival rates in people with brain tumors depend on many different variables:

• Whether the tumor is malignant or benign
• Cancer cell type and location (location affects whether the tumor can be removed surgically or not)
• The tendency to spread and the growth rate (tumor grade)
• Patient's age
• Patient's ability to function
• Duration of symptoms

The outlook is poorer in the very youngest and very oldest patients, although younger patients who survive 2 years after diagnosis have a much better outlook than older patients.

Grading Tumors. Malignant primary brain tumors are classified according to tumor grade. Grade I is the least cancerous, and Grades IV and V are the most dangerous. Grading a tumor attempts to predict its tendency to spread and its growth rate. It is based on the appearance of the tumor cells as seen under a microscope.

• Lower-grade (I and II) tumor cells are well defined and almost normal-shaped. (Some primary low-grade brain tumors are curable by surgery alone, and some are curable by surgery and radiotherapy. Low-grade tumors tend to have the most favorable survival rates and high-grade the least. However, this is not always the case. For example, some low-grade II gliomas are at very high risk for progression.)
• Higher-grade (III and IV) tumor cells are abnormally shaped and are more diffuse, which indicates more aggressive behavior. (High-grade brain tumors usually require surgery, radiotherapy, chemotherapy, and possibly investigational treatments.)
• In tumors that contain a mixture of different-grade cells, the tumor is graded using the highest-grade cells in the mixture, even when there are very few of them.

Biologic Markers. Elevated levels of certain cancer-associated molecules or compounds may be correlated with prognosis. For example, evidence of genetically mutated p53 indicates a poorer prognosis in younger patients with glioblastoma multiforme.

Elevations of epidermal growth factors (EGF) or vascular endothelial growth factors (VEGF) suggest aggressive tumors. High levels of the receptor for EGF (EGFR), in fact, are found in 70% of glioblastoma specimens.

Genetic Profiles of Cancer Cells. Analyses that identify genetic types may soon help clinicians determine if patients with specific brain tumor cells might respond better to one treatment than another. For example, specific genetic profiles of oligodendrogliomas can help predict how patients respond to nitrosourea alkylating drugs such as carmustine. Genetic variation tests are also being used to determine how patients may respond to epidermal growth factor receptor (EGFR) kinase inhibitors, such as erlotinib (Tarceva) and gefitinib (Iressa).

A genetic profile can also help give doctors a better idea of a patient’s prognosis and survival. In a 2006 study of patients with anaplastic oligodendroglioma, the status of specific chromosomal deletions within tumors was a better predictor of survival than which kind of treatment patients received. In fact, the researchers suggested that gliomas be classified according to chromosomal deletion status, and recommended that chromosomal testing be a regular part of diagnosis and treatment decisions.

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Review Date: 10/19/2006
Reviewed By: Harvey Simon, M.D., Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.