brain, spinal cord, and nerve disorders
Tests for Brain, Spinal Cord, and Nerve Disorders
Spinal Tap
Cerebrospinal fluid flows through a channel (the subarachnoid space) between the layers of tissue (meninges) that cover the brain and spinal cord. This fluid, which surrounds the brain and spinal cord, helps cushion them against sudden jarring and minor injury. For a spinal tap (lumbar puncture), a sample of cerebrospinal fluid is withdrawn with a needle and sent to a laboratory for examination. The cerebrospinal fluid is checked for evidence of infections, tumors, and bleeding in the brain and spinal cord. These disorders may change the content and appearance of the cerebrospinal fluid, which normally contains few red and white blood cells and is clear and colorless. For example, the following findings suggest certain disorders: An increase in the number of white blood cells in the cerebrospinal fluid suggests an infection or inflammation of the brain and spinal cord. Cloudy fluid, due to the presence of many white blood cells, suggests Introduction to Meningitis (infection and inflammation of the tissues covering the brain and spinal cord) or sometimes High protein levels in the fluid may result from any injury of the brain, the spinal cord, or a spinal nerve root (the part of a spinal nerve next to the spinal cord). Abnormal antibodies in the fluid suggest Multiple Sclerosis (MS) or an infection. Low sugar (glucose) levels suggest meningitis or cancer. Blood in the fluid may indicate a Overview of Hemorrhagic Stroke —for example, when a bulge in a weakened artery in the brain (aneurysm) bursts (ruptures). An increase in the fluid’s pressure can result from many disorders, including Overview of Brain Tumors and meningitis. Doctors do not do a spinal tap when the pressure within the skull is increased, for example, when there is a mass (such as a tumor or abscess) in the brain. In such cases, a spinal tap may suddenly reduce pressure below the brain. As a result, the brain may shift and be pressed through one of the small openings in the relatively rigid tissues that separate the brain into compartments (called Herniation: The Brain Under Pressure ). Herniation puts pressure on the brain and may be fatal. The medical history and neurologic examination help doctors determine whether herniation is a risk. For example, doctors use an Cerebrospinal fluid flows through a channel (called the subarachnoid space) between the middle and inner layers of tissue (meninges) that cover the brain and spinal cord. To remove a sample of this fluid, a doctor inserts a small, hollow needle between two bones (vertebrae) in the lower spine, usually the 3rd and 4th or the 4th and 5th lumbar vertebrae, below the point where the spinal cord ends, and then into the subarachnoid space—the space between the layers of tissue (meninges) that cover the spinal cord (and brain). Usually, people lie on their side with their knees curled to their chest. This position widens the space between the vertebrae, so that the doctor can avoid hitting the bones when the needle is inserted. Cerebrospinal fluid is then allowed to drip into test tubes, and the samples are sent to a laboratory for examination. For a spinal tap, people typically lie on their side in a bed and draw their knees to their chest. A local anesthetic is used to numb the insertion site. Then, a needle is inserted between two vertebrae in the lower spine below the end of the spinal cord. During a spinal tap, doctors can measure the pressure within the skull. Pressure can be higher than normal in people with Idiopathic Intracranial Hypertension and certain other disorders of the brain and surrounding structures. Pressure is measured by attaching a gauge (manometer) to the needle used for the spinal tap and noting the height of the cerebrospinal fluid in the gauge. A spinal tap may be done for other reasons: To reduce pressure within the skull (intracranial pressure) in people with Idiopathic Intracranial Hypertension None To give a radiopaque contrast agent before Myelography None To give drugs when they are needed to work quickly or to target a specific area of the brain, spinal cord, or meninges—for example, to treat infections or cancer affecting these structures A spinal tap usually takes no more than 15 minutes. About 1 of 10 people develops a headache when standing up after a spinal tap (called a Low-Pressure Headache ). The headache usually disappears after a few days to weeks. However, if the headache is still troublesome after a few days, doctors may inject a small amount of the person's blood into the area around where the spinal tap was done. This procedure, called a blood patch, slows the leakage of cerebrospinal fluid and may relieve the headache. Other problems are very rare. 