Brain Tumors
What is a Brain Tumor?
A brain tumor is defined as a mass of unnecessary and abnormal cells growing in the brain. When a cell divides too rapidly because internal mechanisms that regularly check its growth are damaged, the cell can eventually grow into a tumor. Symptoms or signs of a brain tumor can be caused by pressure on the brain and surrounding tissues or by irritation of neural structures. Extreme irritation of nerve tissue (which may result in seizures) or loss of function may occur.
Types of Brain Tumors
Brain tumors can be classified into two main types: primary or metastatic. The first group - PRIMARY BRAIN TUMORS - includes tumors which come from the tissues of the brain, or its' immediate surroundings. The second group -METASTATIC BRAIN TUMORS - includes tumors which arise elsewhere in the body (such as the breast or lung) and migrate to the brain, usually through the bloodstream. Primary tumors may be benign or malignant. Metastatic tumors are, by definition, cancers (malignancies).
Common benign primary tumors include those originating from the lining of the skull -- also called the meninges, nerves and pituitary gland. Even these tumors may occasionally become malignant. Furthermore, unless treatment results in nearly every tumor cell being destroyed or removed, even benign tumors can recur.
New surgical and radiation techniques can minimize the risk and discomfort of surgery, and may allow the patient to avoid or defer surgery with outcomes similar to those expected from a more traditional surgical approach.
With few exceptions, most tumors that arise from brain tissue are now considered to be malignancies ranging from relatively slow growing, invasive tumors (low grade) to rapidly growing and highly destructive tumors (high grade) such as glioblastomas. In the past, many practitioners referred to the low-grade tumors as being benign. It is now widely recognized that even low grade tumors are rarely cured and may evolve into higher grade tumors over time. Although the overall outlook for patients with these tumors has not changed radically since the 1960s, selected treatments improve the quality of life and have been shown to benefit certain patients. A variety of promising experimental approaches may lead to better treatments in the near future.
Metastatic tumors to the brain affect nearly one in four patients with cancer. Traditionally, the outcome for patients with these tumors was bleak, with the typical survival being only several weeks. More aggressive surgical and innovative radiation approaches can now lead to better quality survival, that is measured in months to years.
Brain tumors in children typically come from different tissues than those affecting adults. Also, treatments that are fairly well tolerated by the adult brain (like radiation therapy) may prevent normal development of a child's brain. Common pediatric tumors include tumors of primitive cells that have not matured into adult cell types (primitive neuroectodermal tumors -- PNETs), tumors of the lining of the brain's fluid sacs, also called "ventricles" (ependymomas) and benign tumors of the supporting cells of the brain (juvenile astrocytomas), as well as other gliomas. Read Classification of Brain Tumors for more detailed information on specific tumors
Treatments for brain tumors
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 more often used for malignant, residual or recurrent tumors, decisions as to what treatment to use are made on an individual basis for each patient and depend on a number of factors. It should also be appreciated that each type of therapy has risks associated with it.
Surgery
It is generally accepted that complete or nearly complete surgical removal of a brain tumor is beneficial for a patient. The surgeon'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, use their hands, etc.). Traditionally, surgeons relied on a large skull opening (or craniotomy) to insure that they could get to the tumor, and subtle differences in the appearance between the tumor and more normal tissue to guide their removal. "Exploratory surgery" was practiced years ago -- and frequently associated with complications.
Another procedure that is commonly done, sometimes before a craniotomy, is called a stereotactic biopsy. This is basically a smaller operation used to obtain tissue, so that a diagnosis can be made. Usually, a frame is attached to the patient's head, a scan is obtained, then the patient is taken to the operating area where a small hole is drilled in 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 first devised which eliminated the need for exploration. These systems assisted the surgeon with guidance, localization and orientation. This information reduced the risks and improved the extent of tumor removal. In many cases it allowed inoperable tumors to be operable at acceptable risk. Some of these systems can also be used to do a biopsy procedure, like the one described above, without having to attach a frame to the skull. One limitation of these systems is that they use a scan (CT or MRI) obtained prior to surgery to guide the surgeon. Thus, they cannot account for movements of the brain that may occur intraoperatively. Investigators are developing techniques using ultrasound, and even doing surgery in MRI scanners, to help update the navigation system data during surgery.
Another type of surgery -- called the placement of a ventriculo-peritoneal shunt may be required for some patients with brain tumors. Everyone has spinal fluid within the brain (and spine) that is slowly circulating or flowing all the time. If this flow becomes blocked, the sacs that contain the fluid -- or "ventricles" -- can start to enlarge, creating increased pressure within the head. This is called hydrocephalus. If left untreated, hydrocephalus can cause brain damage and death. The neurosurgeon may decide to use a shunt to divert the spinal fluid, and therefore reduce the pressure. Usually, the shunt runs from the head -- under the skin -- down to the abdomen, where the fluid is allowed to drain into the abdominal (or "peritoneal" cavity). The shunt is usually 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.
Radiation
The goal of radiation treatments is to selectively kill tumor cells while leaving normal brain tissue unharmed. This may be accomplished in two ways. In standard external beam radiation therapy, multiple treatments of standard-dose "fractions" of radiation are applied to the brain. Each treatment induces damage to both healthy and normal tissue. By the time the next treatment is given, most of the normal cells have repaired the damage while the tumor tissue has not. This process is repeated for a total of 10 to 30 treatments (depending on the type of tumor). Ideally, 98 per cent of the tumor is killed and 98 per cent of the normal tissue survives.
The second way to selectively kill tumor cells is to focus an intense dose of radiation at the tumor from many points around the head. This process is called radiosurgery and uses special computers and delivery devices to accomplish the radiation treatment. Just as a magnifying glass can be used to focus sunlight to a point of intense heat while the rest of the area under the glass remains cool, these devices deliver highly focused doses of radiation to the target area of the tumor. Radiosurgery has been shown to be an effective treatment for many benign and malignant tumors. It has been used both as an alternative to, or combination with, conventional radiation and/or surgery.
Recently, treatments that take advantage of both of these principles of eliminating tumor while sparing normal tissue have been devised. "Stereotactic radiotherapy", or "fractionated radiosurgery", can be used to deliver multiple treatments of low dose radiation while matching the shape of the delivered radiation to the lesion. Theoretically, this should allow tumors to be safely and effectively treated, including tumors than are larger than those that can be managed with conventional radiosurgery.
Reproduced with permission from the American Association of Neurological Surgeons 5550 Meadowbrook Dr., Rolling Meadows, IL 60008; www.neurosurgerytoday.org, 2005