Spontaneous intracranial hypotension (SIH) is a rare cause of headache. SIH presents with postural headache and low cerebrospinal fluid (CSF) pressure. The brain and spinal cord are covered by a tough, watertight membrane called the dura. Inside the dura is the CSF which constantly produced and absorbed in the water spaces of the brain called the ventricles. This fluid surrounds the brain and spinal cord, acting as a shock absorber. It is also a means of supplying nutrients to the brain and removing waste from the brain. When the volume of the cerebrospinal fluid decreases, the brain that normally floats in the fluid hangs inside the skull. This causes headaches and other neurological symptoms.
It is an uncommon disease, with an estimated incidence of 5 per 100,000 per year, and it usually affects young to middle-aged adults, with a female predominance. Intracranial hypotension is of either primary (spontaneous intracranial hypotension) or secondary origin. Spontaneous intracranial hypotension is believed to occur because of trivial trauma and weakness in the dural sac due to spontaneous dural dehiscence and dural tears caused by degenerative causes.
The main symptom of intracranial hypotension is an orthostatic headache that worsens in an upright position, on coughing, laughing, and the Valsalva maneuver. It is also resistant to analgesics. Among other clinical features, there may be impairment of hearing, tinnitus, dizziness, fever, anorexia, nausea, vomiting, photophobia, diplopia, visual field defects, cranial nerve palsies, backache, and neck pain.
It can be seen in connective tissue diseases such as Marfan and Ehlers-Danlos syndrome. It can also occur as a result of dura mater injury due to cranial or spinal surgery, lumbar puncture, spinal anesthesia, ventriculo-peritoneal shunt and craniospinal trauma.
In addition to typical clinical findings, all-around meningeal enhancement can be seen in brain MRI. Also, due to the lower pressure inside the skull, the brain may protrude toward the base of the skull or even partially outward (This may look like a structural problem known as a Chiari malformation). Sometimes, none of these findings may be seen.
There are several conditions that present similarly to spontaneous intracranial hypotension. Postural tachycardia syndrome may present as an orthostatic headache. But in such cases, there is no associated CSF leakage. Excessive drainage of CSF shunts may also present as a clinical picture similar to spontaneous intracranial hypotension. Sometimes it can be confused with meningitis with fever, headache, and irritation of the meninges.
Conservative treatments can be tried in new onset mild to moderate headaches. Strategies involved in conservative treatment aim to reduce CSF leakage. Strict bed rest and avoidance of sitting upright, oral, or intravenous intake of copious amounts of fluids and caffeine and restoring CSF volume may alleviate headache. If this strategy does not improve, an epidural blood patch can be performed. Sometimes surgical repair may be required if these methods do not improve.
Michali-Stolarska ve ark. Diagnostic Imaging and Clinical Features of Intracranial Hypotension – Review of Literature. Pol J Radiol 2017
Liauat MH, Jain S. Spontaneous Intrakranial Hypotension. StatPearls 2022