There are several situations in which intracranial hypotension (low CSF volume/pressure in the head) can develop. This is almost always secondary to a CSF leak at the level of the spine. There are 3 main categories.
Causes of Intracranial Hypotension:
1. Iatrogenic – caused by a medical procedure intentionally or inadvertently.
(a) Post lumbar puncture CSF leak (often known as Post Dural Puncture Headache = PDPH)
This is the most common cause of a spinal CSF leak. The lumbar dura is intentionally punctured for various diagnostic and therapeutic reasons. An example would be a diagnostic lumbar puncture (LP) for a patient thought to have meningitis, to analyze and culture the cerebrospinal fluid. Another would be a lumbar puncture for injection of contrast for a type of spinal imaging known as myelography. A common therapeutic reason would be spinal anesthesia. Most often these holes heal over quickly, but in some cases, they do not.
(b) Dural tears may occur inadvertently at the time of epidural injections. (epidural space is in spinal canal outside of dura and spinal cord)
(c) They may occur at the time of surgery.
(d) CSF shunt over-drainage may cause intracranial hypotension.
2. Traumatic – caused as a result of an injury.
Traumatic leaks have been reported in association with brachial plexus injuries, spinal injuries, sports injuries, falls and chiropractic neck manipulation.
3. Spontaneous – occurring with minimal or no clear precipitant.
Spontaneous spinal CSF leaks may arise with or without obvious precipitant. Common reported events or mechanical factors associated with the onset of symptoms include lifting small or large items, straining, stretching, positional changes, sporting activities, roller coaster rides and falls. Some of these might be categorized as traumatic.
(a) Seemingly spontaneous spinal CSF leaks may be associated with spinal pathology such as calcified disc material or bone spurs. These leaks are often ventral or anterior to the spinal cord. When the underlying cause becomes evident, these are no longer considered “spontaneous”.
(b) There is a growing evidence base suggesting that a significant proportion of spontaneous spinal CSF leaks occur as a result of pre-existing dural weakness. A range of dural defects have been reported at surgery. Electron microscopy of dura has revealed abnormalities in a substantial proportion of cases. Heritable Disorders of Connective Tissue occur at a higher frequency in affected individuals; intracranial hypotension may be the first noted manifestation. Marfan syndrome, Ehlers Danlos syndrome (both classic and hypermobility type) and unspecified heritable disorders of connective tissue have been reported. Patients with spontaneous spinal CSF leaks have been shown to have higher risk of intracranial aneurysms, bicuspid aortic valve and thoracic aortic aneurysms and should be evaluated for Heritable Disorders of Connective Tissue.
Note that cranial CSF leaks (those that arise in the head) are not causally associated with intracranial hypotension.