Intracranial hypotension is a condition in which there is negative pressure within the brain cavity.
There are several possible causes:
Cerebrospinal fluid (CSF) leak from the spinal canal:
A leak following a lumbar puncture (spinal tap).
A defect in the dura (the covering the spinal tube).
Spontaneous, sometimes following exertion such as swinging a golf club.
A congenital weakness.
Following spinal surgery.
Following spinal trauma.
Following a shunt procedure for hydrocephalus.
Ventriculoperitoneal shunt with a low pressure valve.
In some cases, spinal CSF leaks can lead to a descent of the cerebellar tonsils into the spinal canal, similar to a Chiari malformation.
Large spinal dural defects can lead to herniation of the spinal cord into the defect.
The classic symptom is severe headache when upright, which is relieved when lying flat.
Other symptoms can include nausea, vomiting, double vision and difficulty with concentration.
Diagnosis is usually suspected based on the postural dependency of the headache, although in many cases the diagnosis of intracranial hypotension is not considered for some time.
A contrast-enhanced brain magnetic response imaging (MRI) scan typically shows thickened and brightly enhancing meninges (pachymeningeal enhancement). Other findings include descent of the thalamus and cerebellar tonsils.
Continuous intracranial pressure monitoring is definitive for documenting abnormally negative intracranial pressures.
The identification of the site of CSF leak in the spinal canal can be very challenging. In some cases, the site cannot be identified. Methods include:
Dynamic myelography with fluoroscopy and computed tomography (CT).
If the site of the spinal CSF leak can be identified, then options include:
Epidural blood patch, performed by an anesthesiologist pain management specialist.
Surgical repair of the defect.
Over-draining CSF shunts are managed by replacing the valve with one that drains less.
Lumboperitoneal shunts may have to be removed or ligated.
If the cause of the intracranial hypotension can be identified, the outcome following treatment is typically excellent.