Tumors of the Central Nervous System

Saturday, September 5, 2009

In the brain and spinal cord, even benign (noncancerous) tumors can be debilitating or life-threatening. Because the brain and the spinal cord are enclosed within bony structures, there is no room for tissue expansion. Any abnormal growth or swelling puts pressure on delicate tissues and can cause damage and impair function. Benign tumors growing next to critical nerves, brain structures, or blood vessels can compress them and cause problems. Tumors deep in the brain or surrounding tissue can be difficult or even impossible to remove surgically. Cancerous tumors can damage tissue and impair function. They may spread to the brain from other parts of the body or originate in the brain or spinal cord. Except for tumors that have spread from other parts of the body, the cause of brain and spinal cord tumors is unknown. Brain tumors can develop at any age. Spinal cord tumors are less common and are most likely to develop in young and middle-aged adults. Some genetic disorders, such as neurofibromatosis (in which many soft tumors grow from nerves in the skin) and tuberous sclerosis (a disorder causing an acnelike skin condition, mental retardation, and epilepsy), also can cause benign tumors to grow throughout the central nervous system. Tumors of the central nervous system are named for the type of cell or tissue from which they grow. The most common types of tumors in adults include the following: • Chordoma. This slow-growing tumor, which usually appears between ages 20 and 40, develops from tissue in the upper spinal cord. • Glioma. This type of tumor grows from the glial cells in the brain. Gliomas account for about half of all brain tumors and about a fifth of all spinal cord tumors. Gliomas are categorized according to the type of glial cells from which they arise: astrocytoma (from astrocytes), oligodendroglioma (from oligodendroglia cells), ganglioneuroma (from glial cells and immature neurons), and mixed glioma (usually from astrocytes and other glial cells). • Meningioma. Meningiomas develop from the meninges (the thin membranes that cover the brain and spinal cord). Meningiomas affect people of all ages but are most common among those in their 40s. Meningiomas grow slowly and rarely spread. Most are noncancerous. Small meningiomas may not cause any symptoms and may be detected by chance during a brain scan performed for another reason. • Pineal tumor. Pineal tumors grow in the pineal gland, a small structure deep within the brain, and account for about 1 percent of brain tumors. • Pituitary adenoma. The pituitary gland is an endocrine gland in the brain that releases hormones that help control the function of other endocrine glands and influence growth, metabolism, and maturation. Pituitary adenomas are noncancerous tumors that account for about 10 percent of brain tumors. If a pituitary adenoma grows, it can press on the optic nerves and impair side vision. • Schwannoma. This type of noncancerous tumor arises from Schwann cells (cells that form a protective sheath around each neuron). One of the more common forms of schwannoma (an acoustic neuroma) affects the major nerve in the brain that is responsible for balance and hearing. Tumors in the spinal cord are also named according to their location. For example, extradural tumors develop between the vertebrae and the dura (the tough membrane that protects the spinal cord). Tumors within the dura are either extramedullary (outside the spinal cord) or intramedullary (inside the spinal cord). Brain tumors often do not cause symptoms until they have grown large enough to press on tissue, nerves, and blood vessels and affect brain function. When this occurs, a brain tumor can interfere with a specific sense, learned skill, or bodily function. Common symptoms of brain tumors include headaches and numbness or weakness in the arms and legs. The headaches tend to become more severe and last longer as the tumor grows, and they may be accompanied by nausea and vomiting. If the tumor disturbs the normal flow of electrical signals through the brain, seizures can occur. Pressure on certain nerves can lead to vision or hearing problems. Tumors that arise in the cerebrum, especially toward the front of the brain, can alter normal behavior, personality, memory, language, and learning skills. Tumors located toward the base of the brain can lead to weakness or paralysis (partial or complete loss of movement), lack of coordination, or difficulty walking. A tumor on or near the spinal cord can disrupt the flow of sensory information (including pain) to the brain, or movement commands from the brain to the body. Pain caused by a spinal cord tumor may feel like it is coming from elsewhere in the body. Such pain is usually constant, sometimes severe, and often described as burning or aching. Tumor-related changes in sensation include numbness and decreased sensitivity to temperature. Because all muscles are controlled by nerves, tumors in the spinal cord can cause weakness, spasticity (stiffness and restriction of movement), paralysis, difficulty walking, or loss of bladder or bowel control. Tests to diagnose a tumor in the brain or spinal cord include computed tomography (CT) scanning and magnetic resonance imaging]. You may also have cerebral angiography—an examination of the arteries deep inside the brain to assess the tumor’s type and determine its exact position. Another possible test is an electroencephalogram (EEG), in which electrodes are attached to your scalp to monitor the electrical activity in your brain and help determine if the tumor is causing seizures or otherwise affecting brain function. Specialized surgical techniques may be used to remove the tumor. Microsurgery uses a high-power microscope that allows the surgeon to view and access delicate brain tissue. Laser surgery uses powerful, concentrated beams of light to destroy the tumor. Ultrasonic aspiration uses high-frequency sound waves to break up the tumor and an aspirator to vacuum up the pieces. If a tumor cannot be removed and the flow of cerebrospinal fluid inside the brain or skull is blocked, a flexible tube called a shunt will be inserted to reroute and drain the fluid, relieving pressure on the brain. If a tumor is malignant (cancerous) and cannot be removed completely, radiation therapy probably will be used to destroy tumor cells and shrink the tumor. Because radiation therapy destroys only dividing cells, it is particularly useful for treating brain tumors. Doctors use CT scanning and MRI to help focus treatment on the tumor and prevent radiation damage to healthy brain tissue. Chemotherapy (treatment with powerful anticancer drugs) is used to shrink or destroy tumors. Other medications may also be used to relieve problems associated with the tumor. For example, corticosteroids are often prescribed to control the swelling in the brain or spinal cord that can result from a tumor.