What is Spontaneous Intracranial Hypotension?
Spontaneous intracranial hypotension (SIH) is a highly disabling syndrome caused by spinal cerebrospinal fluid (CSF) leak from a dural tear, leaking meningeal diverticulum, or CSF-venous fistula that occurs without any preceding trauma, surgery, or lumbar puncture. 1
Epidemiology and Demographics
- The estimated annual incidence is 3.7 per 100,000 population 1
- Peak age of onset is around 40-47 years 2, 3
- Women are affected more commonly than men (approximately 53% female) 2, 3
Pathophysiology
The fundamental mechanism involves spontaneous CSF leakage from the spine, which occurs because the spine has positive hydrostatic pressure relative to atmosphere, while intracranial pressure is slightly negative in the upright position. 4
The CSF leak leads to three key pathophysiologic changes:
- Decreased CSF volume and pressure causing loss of brain buoyancy within the cranial space 5
- Compensatory venodilation and blood volume expansion to maintain intracranial volume 4
- Downward sagging of the brain toward the foramen magnum with traction on meninges, nerves, and brain parenchyma 4, 5
Clinical Presentation
The hallmark symptom is orthostatic headache, present in approximately 85% of cases, which is absent or minimal when lying down and rapidly worsens to great intensity when sitting or standing. 1, 3
Additional neurological symptoms include:
- Nausea and vomiting 5
- Vertigo and tinnitus 5
- Hearing loss 6
- Marked exacerbation by Valsalva maneuver 5
- Focal cranial nerve palsies 5
- Nerve root distribution weakness 6
Onset patterns vary significantly: 35% present peracutely, 36% subacutely, and the remainder more gradually. 3
Diagnostic Features
Approximately 80% of cases demonstrate MRI features of intracranial hypotension, but the diagnosis should not be excluded based on normal CSF opening pressure, as clinical presentation and imaging findings are more important than measured CSF pressure. 1, 4
The classic MRI findings can be remembered by the mnemonic SEEPS: 2
- Subdural fluid collections
- Enhancement of the pachymeninges (diffuse dural enhancement)
- Engorgement of venous structures
- Pituitary hyperemia
- Sagging of the brain
Prepontine cistern effacement on imaging may predict successful response to epidural blood patch treatment. 3
Underlying Causes and Risk Factors
The CSF leak results from: 1
- Dural tears
- Leaking meningeal diverticula
- CSF-venous fistulas (CVF)
Predisposing conditions include collagen vascular disease, spinal osteophytes, history of bariatric surgery, and idiopathic intracranial hypertension. 4
Mechanical factors combine with underlying connective tissue disorders to cause the CSF leaks. 2
Serious Complications
Cerebral venous thrombosis (CVT) is a rare but life-threatening complication occurring in approximately 2% of SIH cases. 1, 7, 4
Other potential complications include: 5
- Subdural hygroma or hematoma
- Brainstem compression
- Cerebellar tonsillar herniation
- Coma or death in severe untreated cases 8
Clinical Pitfalls
SIH is often misdiagnosed or diagnosed late, prolonging a potentially treatable condition. 1
The diagnosis should be considered in any patient presenting with orthostatic headache, particularly when combined with diffuse dural enhancement on MRI, as these findings are pathognomonic for intracranial hypotension. 4
Differential diagnoses to exclude include postural orthostatic tachycardia syndrome (PoTS), orthostatic hypotension, and migraine. 4