Spontaneous intracranial hypotension: the syndrome and its complications.

Spontaneous intracranial hypotension (SIH) is a syndrome that was largely unknown until the advent of MRI. The incidence of SIH is estimated at 5 per 100,000, which is half the incidence of subarachnoid hemorrhage. The major feature is a postural headache of acute or subacute onset. This headache is absent or minimal when the patient is lying down and rapidly worsens to great intensity when the patient sits or stands. Other features may include nausea, vomiting, vertigo, tinnitus, and marked exacerbation by Valsalva maneuver. SIH is due to a leak of cerebrospinal fluid from a tear in the dural membrane, which occurs most often at the exit zones where the cervical spinal roots leave the subarachnoid space. Other leak sites may be the vestibular system, the cribriform plate, or the pituitary fossa. If the leak continues, the brain loses buoyancy within the cranial space and sags toward the foramen magnum. This, in turn, may produce subdural hygroma or hematoma, brainstem compression, focal cranial nerve palsies, or cerebellar tonsillar herniation. The initial therapy is generally strict bed rest. If this fails, an epidural blood patch is usually successful in sealing the leak and restoring brain buoyancy. A significant minority of patients require a repeat epidural blood patch. If the blood patch fails, a surgical approach may be needed. Repair of the leak and restoration of brain buoyancy will stop the postural headache and, in most cases, will reverse the complications.