Brain Tumors: Primary - Diagnosis

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.

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Other Imaging Techniques. A number of 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 effect 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.