brain, spinal cord, and nerve disorders
Low Pressure Headache
Introduction
Low-pressure headaches result when cerebrospinal fluid is removed during a spinal tap (lumbar puncture) or leaks out because of a cyst or tear in one of the layers of tissues that cover the spinal cord (meninges). Loss of this fluid, which flows around and cushions the brain, reduces pressure around the brain. (See also Overview of Headache .) Most commonly, low-pressure headaches occur after the following: A Spinal Tap (lumbar puncture) A low-pressure headache occurs in up to a third of people who have had a spinal tap, usually hours to a day or two afterward. In a spinal tap, doctors insert a needle between two vertebrae in the lower back, and withdraw a sample of cerebrospinal fluid from the spinal canal. The cerebrospinal fluid, which flows through a channel between the layers of tissues (meninges) that cover the brain and spinal cord, helps cushion and support the brain. After a spinal tap, cerebrospinal fluid sometimes continues to leak out of the tiny hole made by the needle. If fluid leaks out faster than the body can replace it, the amount of fluid around the brain decreases, and the brain may sag downward, stretching the surrounding blood vessels and supporting tissues. This stretching results in a headache. 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. Low-pressure headaches may also occur when other problems cause cerebrospinal fluid to leak out: A cyst in or near the meninges where a nerve comes out of the spinal cord bursts. Cysts sometimes burst when people cough or sneeze because coughing and sneezing cause the pressure within the cerebrospinal fluid to suddenly increase. Cerebrospinal fluid sometimes leaks spontaneously—for no apparent reason. The meninges are torn during an injury, particularly when the head or face is injured. Low-pressure headaches are intense. They occur when people sit or stand and may be relieved by lying flat. People usually also have a stiff, painful neck and nausea and may vomit. 