What is a positional headache?
The headache associated with intracranial hypotension (low fluid pressure inside the head) secondary to a spinal cerebrospinal fluid (CSF) leak is usually positional—that is, it is head pain that is worse when upright but improved when horizontal. This is sometimes called an orthostatic headache, as the term “orthostatic” means “of, relating to, or caused by an upright posture.”
When there is a tear or hole in the dura mater (the connective tissue that normally holds the fluid in around the brain and spinal cord), this allows CSF to leak out, resulting in a loss of CSF volume. When a person with intracranial hypotension is upright, most of the remaining CSF surrounds the spinal cord. This means there is less CSF available in the head to provide buoyancy to the brain. The resulting descent of the brain causes traction on pain-sensitive structures of the head. Common associated symptoms include nausea and vomiting, neck pain or stiffness, hearing changes, imbalance, photophobia (sensitivity to light), phonophobia (sensitivity to sound), interscapular pain (between the shoulder blades), pain or numbness of arms, brain fog, and dizziness.
How do you know if a positional headache is due to a spinal CSF leak?
When a patient goes to a physician with symptoms of a new onset positional headache, spontaneous intracranial hypotension secondary to a spinal CSF leak should always be considered. In about 80% of patients with spinal CSF leak, MRI imaging of the brain reveals imaging findings consistent with that diagnosis, while 20% will have normal imaging. Spinal imaging with MRI or with CT myelography or may or may not reveal evidence of a spinal CSF leak.
When imaging evidence of a spinal CSF leak is not evident, there are three possibilities:
- The leak may be a CSF venous fistula type of leak, where the CSF drains directly from the intrathecal space into the epidural veins. Because the epidural space is bypassed, these leaks will not usually be evident on routine CT myelography or on MR imaging of the spine, but may be seen with digital subtraction imaging;
- The leak may be a very slow flow leak below the level of imaging resolution. In such cases, repeat imaging or delayed may be revealing; or
- There is no CSF leak and there is another cause for the orthostatic headache and other symptoms.
Are there other conditions that cause positional headache?
In cases where a CSF leak cannot be confirmed after thorough evaluation, there are other known causes of positional (or orthostatic) headache that may be considered.
Neurologists do see patients with cervicogenic headaches that can be worse when upright. Cervicogenic means “arising from the cervical spine” and may be from cervical structures including the intervertebral discs, facet joints, skeletal muscles, connective tissues, and neurovascular structures.
Another cause of orthostatic headache that is not secondary to a spinal CSF leak is positional orthostatic tachycardia syndrome (POTS). POTS is a type of dysfunction of the autonomic nervous system that causes a variety of symptoms, many of which are exacerbated with upright posture. In some cases, the positional headache is one of the most prominent symptoms. Complicating this diagnostically is the fact that patients with spinal CSF leaks are often effectively bedridden and can develop secondary POTS as a result of deconditioning.
Chiari malformation is a condition in which brain tissue extends into the spinal canal. This may be congenital or it may be acquired from loss of CSF volume. Acquired Chiari secondary to a spinal CSF leaks is usually reversible with successful treatment of the CSF leak. A subset of patients that have had Chiari decompression surgery may have orthostatic headache.
There are some other rare causes of orthostatic headache that are beyond the scope of this discussion.
Spontaneous spinal CSF leaks arise in many cases from a weakness of the dura, the connective tissue outer layer of the meninges surrounding the spinal cord and brain. An underlying heritable disorder of connective tissue is found or suspected in many of these patients. Ehlers Danlos syndrome (EDS) is one of several heritable disorders of connective tissue seen in spontaneous spinal CSF leak patients. Of importance is the observation that EDS patients also have a higher prevalence of POTS/dysautonomia as well as Chiari malformation. EDS patients may have one or more of these three causes of orthostatic headache, complicating diagnosis and treatment.
In summary
A new onset headache that is worse when upright should result in evaluation for a spontaneous spinal CSF leak, since this can be very disabling and is treatable. Other causes of orthostatic headache are known and may be considered when a CSF leak is not evident on thorough evaluation with imaging. In some situations, the diagnostic process can be challenging.