By Dr Ananya Mandal, MD
On presenting with symptoms of brain cancer a battery of tests are advised to reach a diagnosis.
Initial diagnosis methods
The attempt to reach a diagnosis begins with a thorough physical examination. The doctor may also enquire about your history and your relevant family history of brain tumors or cancers. They may also send you for routine blood tests.
A neurological test may also be prescribed. This involves testing vision, alertness, hearing, muscle power and strength, reflexes and coordination.
Eyes are often examined in detail using an instrument called the ophthalmoscope. This examines the back of the eyes called the retina. If the brain tumor creates pressure over the back of the eyes the ophthalmoscopy shows the change. (1)
Radiological and imaging techniques
The most commonly applied techniques are radiological or imaging techniques. These include the MRI or the Magnetic Resonance Imaging technique and the CT scan or the Computed tomography image of the brain.
The MRI is a machine that uses an electromagnetic device that can take detailed pictures of the brain. This may be made more specific by the use of a dye known as a contrast dye that is injected into a blood vessel of the arm or leg. The dye travels up the blood vessels of the brain and shows up a clearer and more detailed picture of the brain with its blood vasculature.
Usually cancers and tumors have deranged blood vessels and this often shows up in dye enhanced MRI images. This type of imaging is often called MRA or Magnetic resonance angiograms.
An MRI with gandolinium is most commonly done. This involves the use of the chemical gandolinium that, when administered, tends to cluster in and around tumor cells highlighting them on imaging.
A CT scan is a less sophisticated imaging technique than an MRI and is like a detailed X ray that shows parts of the brain and the tumor. Contrast dyes may also be used with CT scans. (1)
A spinal tap or lumbar puncture may also provide aid in diagnosis. In this, the physician inserts a needle in the patient’s back under local anesthesia. This long and thin needle is used to withdraw some of the cerebrospinal fluid. This CSF circulates all over the brain and spinal cord and may provide clues regarding the tumor on examination under microscope.
Sometimes a neuroendoscopy may be performed. This involves insertion of a fine tube with a camera on its tip. It is inserted into the spaces within the brain called ventricles under the guidance of the camera. This technique may be used to remove a fluid flow blockage, to relieve pressure or to take a sample biopsy. (1)
A biopsy involves removal of a bit of the tumor tissue and examination under the microscope.
The biopsy can reveal the type, grade and original cells of the tumor or cancer. It is sometimes the surest way to diagnose the brain tumor and helps neurologists plan therapy in a patient.
A biopsy may be done during an ongoing brain surgery for the removal of the tumor. In some cases a stereotactic biopsy may also be performed. This includes putting the patient under general anesthesia and using boring instruments under guidance of MRI or CT scan to reach the tumor and take a biopsy specimen from the tumor. This is usually favored in patients who have an inoperable brain tumor.
Tumors or cancers that lie in vital areas of the brain, like the brain stem, may not allow a biopsy at all due to the raised risks of damage and death. In these patients imaging techniques guide management of the patient. (2)
Once the biopsy tissue is extracted it can be subjected to: immunohistochemistry study to detect type of tumor; electron microscopy for cell changes detection; cytogenetic analysis to see cell changes at the level of genes. (3)
Tumor marker tests
There are some tumor marker tests. These are procedures where blood, urine or tissue samples are checked to see if they are high in certain chemicals or markers that are typical of tumors.
These are especially useful in diagnosis of germ cell tumors that may occur in the brain. There are some genetic tests as well that determine the inherited nature of some brain tumors.
There are SPECT scans (single photon emission computed tomography scan) that use a camera linked to a computer that makes a three dimensional picture of the brain that shows up the tumor.
A PET scan (positron emission tomography scan) can also be used to diagnose a deep seated brain tumor. This procedure uses radioactive sugar that is injected into a vein for diagnosis. (3)
Edited by April Cashin-Garbutt, BA Hons (Cantab)
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Last Updated: May 22, 2012