What causes the headache?
Your brain and spinal cord are surrounded by fluid. The fluid is called the cerebrospinal fluid (CSF).
- For an epidural, a needle is used to inject local anaesthetic just outside the membrane that surrounds the spinal cord (this membrane is called the dura). If the needle accidentally passes through the dura, a small hole is made. CSF can leak out through the hole.
- When a spinal injection is given, a very fine needle is deliberately inserted through the dura. The hole made by a spinal needle is very small and no CSF usually leaks out. But sometimes the hole is big enough to cause some leakage of CSF.
If too much fluid leaks out through the hole in the dura, the pressure in the rest of the fluid around the brain is reduced. This causes a typical headache, which is called a post-dural puncture headache. If you sit up, the pressure around your brain is reduced even more. Therefore, sitting or standing often makes the headache worse. On the other hand, lying flat will often improve this type of headache.
Although the hole in the dura will usually seal over in a number of weeks, it is not usually a good idea to wait for this to happen. The brain is cushioned by the CSF around it. If the headache is left untreated, this cushioning effect is not present and bleeding into or around the brain (a subdural haematoma) may occasionally occur. A fit (seizure) can also happen but this is rare. Therefore, it is very important to treat a post-dural puncture headache.
Further reading and references
Headache after a spinal or epidural injection; Royal College of Anaesthetists, February 2017
Cook TM, Counsell D, Wildsmith JA; Major complications of central neuraxial block: report on the Third National Audit Project of the Royal College of Anaesthetists. Br J Anaesth. 2009 Feb102(2):179-90. doi: 10.1093/bja/aen360. Epub 2009 Jan 12.
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