Between the dura and the spinal cord itself is a supportive pool of fluid called cerebrospinal fluid (csf). CSF is produced at a rate of 2 - 3 tablespoons per hour by structures (called choroid
plexus) in the brain.
" is a procedure to control pain (usually during childbirth) in which pain-relieving medication is placed in the low back between the dura and the overlying tissue (mostly the ligaments that help support the spine bones). Because the dura is smashed up against the overlying tissue by the csf, the epidural "space" is really not a space at all until the epidural medicine is squirted into it, kind of like how a liquid-filled blister forms in the "space" between the layers of the skin.
The dura mater is about 250 microns thick (about 1/100th of an inch) at the region of the spine where most epidurals are placed. 250 microns is about twice the thickness of an "average" human hair. The length of the needle used for an epidural is about 8 cm or 3 inches for average-sized patients, and can be much longer for obese patients.
Because the thickness of the dura is so small relative to the other dimensions involved, puncturing the dura can and does happen. In fact, another type of anesthesia
, often called a "spinal" involves exactly this. Intentional dural punctures (also known as "lumbar punctures" or "spinal taps") are a very important test used many times on a daily basis in most hospitals.
After a dural puncture, somewhere between about 18 and about 50% of people develop headache
. The headache has characteristic patterns, including a relationship in time to the dural puncture. No one really knows what causes the headache that follows a dural puncture. In 1898, a doctor named bier was the first (that we know of) to describe a post-lumbar puncture
headache after trying one of the first lumbar punctures on himself. He was also the first to propose that the headache might be caused by leakage of cerebrospinal fluid through the hole made by the needle. This has never been proven. On one hand, it is hard to imagine how a hole that is less than 1/2 of a millimeter could leak enough CSF to cause symptoms, or how a hole that is the same size as those used to give shots could not instantly heal up. On the other hand, a procedure called an epidural blood patch (in which a relatively large quantity of the patient's blood is taken from a vein and injected into the epidural space) seems to be up to 70% effective in relieving headache after lumbar puncture.
While it is possible that a CSF leak could cause headache a year after a dural puncture, it is unlikely. There are many other sources of headache that occur at a much greater frequency in the general population. There are ways to check for CSF leaks and to measure the pressure of the CSF (which should be low if there is a leak). If appropriate and effective treatments for post-dural puncture headache haven't worked over many months, this is another reason to think that dural puncture may not be the cause of the headache.
A visit to a neurologist, particularly one with expertise in headache, may offer a fresh look at this old problem, and may lead to new answers.