Any tear or hole in the membrane that surrounds the brain and spinal cord (dura) can allow the fluid that surrounds those organs to leak.
This fluid is called the cerebrospinal fluid (CSF). When it leaks out, the pressure around the brain and spinal cord drops.
Causes of leakage through the dura include:
Certain head, brain, or spinal surgeries
Head injury
Placement of tubes for epidural anesthesia or pain medications
Spinal tap (lumbar puncture)
Sometimes, no cause can be found. This is called a spontaneous CSF leak.