The first step in the identification of a brain tumor involves a neurological exam.
This exam entails a series of tests which measures nervous system function and physical and mental alertness. If the results of this exam are abnormal, a brain scan will be administered by a neurological expert.
A brain scan consists of a picture of the brain’s internal structures. A specialized imaging machine produces a scan in a manner similar to a digital camera taking a photo. With the use of computer technology, a scan creates an image by photographing the brain from various angles.
Some scans use contrast dye injected into the patient’s vein, which assists the neurosurgeon in differentiating between normal and abnormal brain tissue. Abnormal or diseased brain tissue absorbs greater amounts of dye than healthy tissue.
The neurological exam, imaging (brain scans), as well as the evaluation of brain tissue via biopsy, are all methods for determining the presence of a brain tumor. Brain tumors are classified from the least aggressive (benign) to the most aggressive (malignant). The cell type of origin or the location of the tumor determines the classification of a brain tumor. Identifying the type of tumor determines the most appropriate type of treatment.
Below are the most common scans used for brain tumor diagnosis:
MRI (Magnetic Resonance Imaging)
The MRI uses magnetic fields and computers to scan and capture images of the brain. While it utilizes film, it does not use x-rays. The scan provides images of various planes, which allow the doctor to create a three-dimensional image of the tumor. An MRI detects signals emitted from both normal and abnormal tissue, which results in clear images of most tumors.
CT or CAT Scan (Computed Tomography)
The CT scan is a combination of advanced x-ray and computer technology, usually with the use of iodine as a contrast agent in this case. CT scans can show soft tissue, bone and blood vessels combined. CT images can detect swelling, bleeding and bone and tissue calcification, as well as being effective in determining some types of tumors.
PET Scan (Positron Emission Tomography)
The PET scan creates a picture of the brain’s activity by measuring the rate at which a tumor absorbs glucose (a sugar). This is in contrast to the other imaging techniques, which measure the structure of a brain tumor. In the case of a PET scan, the patient is injected with deoxyglucose, a substance labeled with radioactive markers. The PET scan relays the measured brain activity to a computer, which creates a live image. A neurosurgeon can use PET scans to determine the difference between scar tissue, recurring tumor cells and necrosis (i.e. cells destroyed by radiation treatments).
A biopsy surgically removes a sample of tissue taken from a tumor site in order to be examined under a microscope. The biopsy provides information on the types of abnormal cells present in the tumor. The biopsy, the most accurate method of obtaining a tumor diagnosis, is administered to determine the type and grade of a tumor.
A craniotomy is performed as part of an open biopsy. A craniotomy consists of removing a piece of the skill in order to gain access to the brain. Following the tumor resection (completely removed) or if the tumor is debulked (partially removed), the bone is usually returned to place.
A closed biopsy (also referred to as a sterotactic or needle biopsy) may be performed for difficult to reach areas of the brain in which a tumor is located. In a closed biopsy, the neurosurgeon drills a small hole into the skull, through which a narrow hollow needle is passed into the tumor in order to remove a tissue sample.
Once a biopsy sample is obtained, a pathologist examines the tissue under a microscope in order to analyze the brain tissue and make a diagnosis. If necessary, due to a complicated case or one in which there is more than one grade of tumor cells located in the same tumor, the tissue is sent on for further expert analysis.