Spontaneous intracranial hypotension (SIH) was first reported by Schaltenbrand in 1938 and is characterized by intracranial hypotension due to cerebrospinal fluid (CSF) leakage from the spine.
Epidemiology:
Three main mechanisms of CSF leakage (Schievink classification):
The annual incidence is estimated at 5 per 100,000 people (1/20,000)1), but as high-resolution imaging becomes more widespread, the actual frequency may be even higher. Asymptomatic or mild cases are also thought to be included.
The frequency of symptoms in a Japanese cohort is shown below3).
| Symptom | Frequency |
|---|---|
| Headache (orthostatic) | 98.5% |
| Dizziness/vertigo | 50.5% |
| Nausea | 49.0% |
| Balance disorder | 42.6% |
| Posterior neck pain | 34.2% |
Other symptoms may include horizontal diplopia (abducens nerve palsy), tinnitus/hearing changes (involvement of cranial nerve VIII), facial numbness, blurred vision, and visual field defects. In severe cases, parkinsonism, coma, and frontotemporal dementia-like symptoms have also been reported.
Characteristics of orthostatic headache: Worsens in the upright position and improves or resolves in the supine position.
Ophthalmic involvement (ocular symptoms in 42% of SIH patients):
Trendelenburg test: Resting in a 10–20 degree head-down position for 5 minutes causes orthostatic headache to disappear or improve. Useful as an auxiliary diagnostic finding.
Ocular symptoms occur in 42% of SIH patients, with the most common being diplopia due to abducens nerve palsy. The trochlear nerve (cranial nerve IV) is frequently involved, and the optic nerve is rarely affected. Importantly, 97% of these ocular symptoms improve with correction of CSF pressure (e.g., bed rest, epidural blood patch).
Causes of CSF leakage:
Major risk factors:
A Danish report observing 36 SIH patients found that 4 cases (11%) developed SIH after airplane travel, with a temporal association2). It is suggested that the decrease in cabin pressure (about 0.8 atm, equivalent to cruising altitude) may promote rupture of meningeal diverticula. However, large-scale multicenter studies have not been conducted, and a causal relationship has not been established.
Comparison of diagnostic criteria:
| Diagnostic criteria | Major requirements |
|---|---|
| 2008 AJNR criteria | ① Extramedullary CSF confirmation on spinal imaging ② Head MRI findings suggestive of SIH + low opening pressure (<60mmH₂O)/dural diverticulum/improvement after EBP ③ Typical orthostatic headache + at least 2 of the items in ② |
| ICHD-3 criteria | Orthostatic headache + CSF pressure <60mmH₂O or imaging evidence of CSF leakage3) |
| Japanese diagnostic criteria | Orthostatic headache + dural enhancement or CSF pressure <60mmH₂O for “probable”3) |
Head MRI findings (in order of sensitivity):
MR myelography: specific findings such as the floating dural sac sign and dinosaur tail sign. Useful for identifying the leakage site 3).
Ultrasound: In SIH patients, the optic nerve sheath diameter (ONSD) decreases by 0.5 mm when moving from supine to upright position. No change in healthy controls.
Occult SIH (oSIH): typical orthostatic headache but normal imaging findings. Meta-analysis shows imaging evidence of CSF leakage in only 48–76% of cases 5).
Differential diagnosis: meningitis (bacterial, fungal, aseptic), autoimmune diseases (RA, SLE), sarcoidosis, tuberculosis, brain tumors (meningioma, en plaque lymphoma), Chiari type I malformation (differentiated by measuring the mamillopontine distance; shortened in SIH 6)).
Conservative Therapy
Rest and fluid intake: conservative therapy includes bed rest and intravenous fluids 3).
Abdominal binder.
Medications: caffeine, theophylline, analgesics, NSAIDs.
Kampo medicine (Goreisan): inhibits aquaporin-4 channels for water retention 3).
Steroids: prednisone 1 mg/kg/day for 5 days (tapered over 7 days). The overall success rate of conservative treatment is only about 28% 1).
Epidural Blood Patch (EBP)
Effectiveness: Improvement in 87% after targeted EBP. Blind EBP improves in 52%.
Method: Inject 10–15 mL of autologous blood into the lumbar epidural space. For cervical leaks, inject 20–40 mL into the thoracolumbar epidural space.
Recurrence: 25% recur within 8 years after targeted EBP. Repeat EBP is successful.
Occult SIH (oSIH): Empirical EBP leads to improvement in 66.7% at discharge and 90.5% at 3 months5).
Surgical Treatment
Indications: After two or more failed EBPs. Clear identification of the leak site is necessary.
Procedures: Meningeal diverticulum ligation, direct repair of dural tear, epidural fibrin glue injection, duroplasty.
Vascular malformation-related: Fibrin glue patch, liquid embolization (n-BCA), surgical ligation. Standard EBP is often insufficient for fistula closure6).
Targeted EBP improves 87% of cases, while blind EBP improves 52%5). Improvement rates after the first EBP vary from 25% to 90% across studies. If there is no improvement after the first session or if recurrence occurs, repeat EBP is performed. For occult SIH (oSIH), empirical EBP led to improvement in 90.5% at 3 months5).
Normal CSF dynamics:
SIH pathophysiology according to the Monroe-Kellie hypothesis: Since intracranial volume is fixed (the skull is rigid), a decrease in CSF volume is compensated by an increase in the volume of low-resistance structures (veins around the brain and pituitary, dural venous sinuses)4)8). This compensatory mechanism produces characteristic MRI findings.
Mechanisms of CSF leakage:
Mechanism of superficial CNS hemosiderosis: Brain sagging → bleeding from bridging veins, or bleeding from the epidural venous plexus around the dural defect → repeated subarachnoid hemorrhage4).
Tonello et al. (2022) reported a 38-year-old male with C2-level CSF leak who received prednisone 1 mg/kg/day for 5 days followed by a 7-day taper, and imaging at 1 month showed near-complete resolution of the CSF leak 1). Multiple mechanisms of action are hypothesized, including improvement of cerebral edema/inflammation, fluid retention, and promotion of CSF reabsorption. Currently, this is at the case report level, and prospective randomized studies are needed.
A temporal association between air travel and SIH onset was confirmed in 4 of 36 cases (11%) 2). It is hypothesized that decreased cabin pressure may promote rupture of meningeal diverticula, but large-scale multicenter case-control studies are needed.
Accurate nomenclature and classification of CSF-venous malformation fistulas and CSF-lymphatic malformation fistulas have been proposed 6). For lymphatic malformations, reduction with mTOR inhibitors (e.g., sirolimus) has been demonstrated, offering potential treatment for associated CSF leaks 7).
For pediatric oSIH presenting with typical orthostatic headache but no detectable leak on MRI or CT myelography, the efficacy of empirical EBP has been reported 5). Efforts are underway to visualize previously undetectable leaks using newer imaging techniques such as digital subtraction myelography (DSM) and dynamic CT myelography 5).
