Brain Tumors

Types of Brain Tumors

A brain tumor, known as an intracranial tumor, is an abnormal mass of tissue in which cells grow and multiply uncontrollably, seemingly unchecked by the mechanisms that control normal cells. More than 150 different brain tumors have been documented, but the two main groups of brain tumors are termed primary and metastatic.

Primary brain tumors include tumors that originate from the tissues of the brain, or the brain's immediate surroundings. Primary tumors are categorized as glial (composed of glial cells) or non-glial (developed on or in the structures of the brain, including nerves, blood vessels, and glands) and benign or malignant.

Metastatic brain tumors include tumors that arise elsewhere in the body (such as the breast or lungs) and migrate to the brain, usually through the bloodstream. Metastatic tumors are considered cancer and are malignant.

Metastatic tumors to the brain affect nearly one in four patients with cancer, or an estimated 150,000 people a year. Up to 40 percent of people with lung cancer will develop metastatic brain tumors. In the past, the outcome for patients diagnosed with these tumors was very poor, with typical survival rates of just several weeks. More sophisticated diagnostic tools, in addition to innovative surgical and radiation approaches, have helped survival rates expand up to years; and also allowed for an improved quality of life for patients following diagnosis.

Pediatric Brain Tumors

Brain tumors in children typically come from different tissues than those affecting adults. Treatments that are fairly well-tolerated by the adult brain (such as radiation therapy) may prevent normal development of a child's brain, especially in children younger than age five.

Some types of brain tumors are more common in children than in adults. The most common types of pediatric tumors are medulloblastomas, low-grade astrocytomas, ependymomas, craniopharyngiomas, and brainstem gliomas.

Brain Tumor Causes

Brain tumors are thought to arise when certain genes on the chromosomes of a cell are damaged and no longer function properly. These genes normally regulate the rate at which the cell divides (if it divides at all) and repair genes that fix defects of other genes, as well as genes that should cause the cell to self-destruct if the damage is beyond repair. In some cases, an individual may be born with partial defects in one or more of these genes. Environmental factors may then lead to further damage. In other cases, the environmental injury to the genes may be the only cause. It is not known why some people in an "environment" develop brain tumors, while others do not.

Once a cell is dividing rapidly and internal mechanisms to check its growth are damaged, the cell can eventually grow into a tumor. Another line of defense may be the body's immune system, which optimally would detect the abnormal cell and kill it. Tumors may produce substances that block the immune system from recognizing the abnormal tumor cells and eventually overpower all internal and external deterrents to its growth.

A rapidly growing tumor may need more oxygen and nutrients than can be provided by the local blood supply intended for normal tissue. Tumors can produce substances calledangiogenesis factors that promote the growth of blood vessels. The new vessels that grow increase the supply of nutrients to the tumor, and, eventually, the tumor becomes dependent on these new vessels. Research is being done in this area, but more extensive research is necessary to translate this knowledge into potential therapies.

Symptoms

Symptoms vary depending on the location of the brain tumor, but the following may accompany different types of brain tumors.

  • Headaches that may be more severe in the morning
  • Seizures or convulsions
  • Difficulty thinking, speaking or articulating
  • Personality changes
  • Weakness or paralysis in one part or one side of the body
  • Loss of balance or dizziness
  • Vision changes
  • Hearing changes
  • Facial numbness or tingling
  • Nausea or vomiting
  • Confusion and disorientation

Diagnosis

Sophisticated imaging techniques can pinpoint brain tumors. Diagnostic tools include computed tomography (CT or CAT scan) and magnetic resonance imaging (MRI). Intraoperative MRI also is used during surgery to guide tissue biopsies and tumor removal.Magnetic resonance spectroscopy (MRS) is used to examine the tumor's chemical profile and determine the nature of the lesions seen on the MRI. Positron emission tomography (PET scan) can help detect recurring brain tumors.

Sometimes the only way to make a definitive diagnosis of a brain tumor is through a biopsy. The neurosurgeon performs the biopsy and the pathologist makes the final diagnosis, determining whether the tumor appears benign or malignant, and grades it accordingly.

Brain Tumor Treatment

Brain tumors (whether primary or metastatic, benign or malignant) are usually treated with surgery, radiation, and/or chemotherapy — alone or in various combinations. While it is true that radiation and chemotherapy are used more often for malignant, residual, or recurrent tumors, decisions as to what treatment to use are made on a case-by-case basis and depend on a number of factors. There are risks and side effects associated with each type of therapy.

Surgery

It is generally accepted that complete, or nearly complete, surgical removal of a brain tumor is beneficial for a patient. The neurosurgeon's challenge is to remove as much tumor as possible, without injuring brain tissue important to the patient's neurological function (such as the ability to speak, walk, etc.). Traditionally, neurosurgeons open the skull through a craniotomy to insure they can access the tumor and remove as much of it as possible.

Another procedure that is commonly performed, sometimes before a craniotomy, is called astereotactic biopsy. This smaller operation allows doctors to obtain tissue in order to make an accurate diagnosis. Usually, a frame is attached to the patient's head, a scan is obtained, and then the patient is taken to the operating area, where a small hole is drilled into the skull to allow access to the abnormal area. A small sample is obtained for examination under the microscope.

In the early 1990s, computerized devices called surgical navigation systems were introduced. These systems assisted neurosurgeons with guidance, localization, and orientation for tumors. This information reduced the risks and improved the extent of tumor removal. In many cases, surgical navigation systems allowed previously inoperable tumors to be excised with acceptable risks. Some of these systems can also be used for biopsies without having to attach a frame to the skull. One limitation of these systems is that they utilize a scan (CT or MRI) obtained prior to surgery to guide the neurosurgeon. Thus, they cannot account for movements of the brain that may occur intraoperatively. Investigators are developing techniques using ultrasound and performing surgery in MRI scanners to help update the navigation system data during surgery.

Intraoperative Language Mapping is considered by some as a critically important technique for patients with tumors affecting language function, such as large, dominant-hemisphere gliomas. This procedure involves operating on a conscious patient and mapping the anatomy of their language function during the operation. The doctor then decides which portions of the tumor are safe to resect. Recent studies have determined that cortical language mapping may be used as a safe and efficient adjunct to optimize glioma resection while preserving essential language sites.

Ventriculoperitoneal Shunting may be required for some patients with brain tumors. Everyone has cerebrospinal fluid (CSF) within the brain and spine that is slowly circulating all the time. If this flow becomes blocked, the sacs that contain the fluid (the ventricles) can become enlarged, creating increased pressure within the head, resulting in a condition called hydrocephalus. If left untreated, hydrocephalus can cause brain damage and even death. The neurosurgeon may decide to use a shunt to divert the spinal fluid away from the brain and, therefore, reduce the pressure. The body cavity in which the CSF is diverted usually is the peritoneal cavity (the area surrounding the abdominal organs). The shunt usually is permanent. If it becomes blocked, the symptoms are similar to that of the original condition of hydrocephalus and may include headaches, vomiting, visual problems, and/or confusion or lethargy, among others.

 

Information courtesy of the American Association of Neurological Surgeons

 

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