The dura is the strong, flexible covering of the spinal cord inside the bones of the spine. Certain medical procedures require a needle to puncture the dura, and other medical techniques can accidentally puncture the dura. As the dura contains the cerebrospinal fluid (CSF) that bathes and protects the nerves inside the spine and brain, damage to it can cause a CSF leak. A headache can result if the leak lowers the pressure inside the dura, and this post-dural-puncture headache can last for weeks and cause discomfort and pain during this time. Procedures that carry a chance of post-dural-puncture headache include epidurals for laboring women and lumbar punctures for test reasons.
A human spine is composed of bony structures that are hollow in the inside. Nerves run through the hollows of the bones, and these nerves are surrounded and protected by CSF. Outside of the nerves is the dura layer, which is made up of strong connective tissue fibers. Normally, the dura remains intact, unless it is damaged by injury or by insertion of spinal needles.
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Some medical tests involve the use of needles to reach the interior area of the spine. For laboring women undergoing epidurals, the needle is supposed to get into the epidural space around the dura, and not into the dura. People who require anesthetic for medical procedures, or for pain management, may also receive spinal injections. Some cases, such as those people who may be suffering from meningitis, require a deliberate puncture of the dura so a doctor can remove a sample of CSF to check for infection.
Whether the dura is punctured deliberately or accidentally, the post-dural-puncture headache has a relatively high tendency to occur as a side effect. When spinal injection techniques were first used at the end of the 19th century, post-dural-puncture headaches were very common. As needles became smaller and were made from designs that were less likely to cause accidental damage, the risk of the headaches fell. In patients, the highest risk exists for people undergoing deliberate dural puncture, followed by women receiving epidurals. The risk for people receiving anesthesia in the spinal area tends to be much lower than the other procedures.
As of 2011, the exact way in which a dural puncture produces a post-dural-puncture headache is not known. A reduction in CSF pressure does appear to be a cause, but the reasons for pain in the head are not definite. One possibility is a decrease in the physical support for brain structures, which may produce pain signals when unsupported as normal. Alternatively, the reduction of CSF pressure results in an increase in blood vessel diameter, which is also capable of producing pain in the head.