How is brain tumor diagnosed?
Brain tumor is diagnosed through a combination of symptoms and evaluation of neurological functions. Doctors consider the possibility of a brain tumor in people who have had a seizure for the first time or who have the characteristic symptoms. Although doctors can often detect brain dysfunction by performing a physical examination, other procedures are needed to
diagnose a brain tumor. 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 physician will also test mental state and memory.
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.
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.
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. PET is not routinely used for diagnosis, but it may supplement MRIs to help determine tumor grade after a diagnosis. 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.
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.
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.