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.
How a Spinal Tap Is Done
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.
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 allowed to drip into a test tube, and the sample is 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.
- A doctor's evaluation
- Sometimes imaging tests
Doctors base the diagnosis of low-pressure headaches on the symptoms and the situation.
If people have had a spinal tap, the diagnosis is usually obvious, and testing is rarely needed.
If they have not had a spinal tap, imaging tests of the brain, such as magnetic resonance imaging (MRI), may be done. Before the imaging test, a contrast agent is injected into a vein, usually in an arm or a hand. The contrast agent is used to provide greater detail.
- Pain relievers
- Fluids and caffeine
- Sometimes an epidural blood patch
If people have a headache after a spinal tap, they are given pain relievers (analgesics). Lying flat as much as possible helps minimize pain. They are given fluids and caffeine, which increases the production of cerebrospinal fluid. Fluids are given by mouth or, if people are very dehydrated, intravenously.
If the headache persists after such treatment, doctors may inject a small amount of the person’s blood into the space between the spine and the meninges in the lower back. This procedure, called an epidural blood patch, slows the leakage of cerebrospinal fluid, regardless of where the leak is or what caused it.
Surgery to repair a leak is rarely required.