Spontaneous Intracranial Hypotension

Spontaneous intracranial hypotension is a syndrome of low cerebrospinal fluid volume or pressure, usually from a spinal cerebrospinal fluid leak without a clear cause. It typically causes an orthostatic headache that worsens when upright and eases on lying flat.

The incidence is about 4 to 5 in every 100,000 people each year. It is under diagnosed, affects women about twice as often as men, and has a peak onset at 30 to 50 years.

Causes. Dural tears from a calcified disc or osteophyte (ventral leak), meningeal diverticula, cerebrospinal fluid venous fistulae, connective tissue disorders (Marfan, Ehlers-Danlos syndrome), minor trauma and no cause found in many.

Complications. Subdural collections, cerebral venous thrombosis, superficial siderosis, cerebellar haemorrhage and brain sagging causing a frontotemporal dementia like syndrome.

Pathophysiology.

Loss of cerebrospinal fluid reduces its cushioning of the brain, which sags and traction on pain sensitive structures causes headache; compensatory venous dilatation and subdural collections follow.

The Monro-Kellie relation explains the distension of venous structures and the pachymeningeal enhancement.

• Orthostatic headache, usually occipital or diffuse, starting within minutes of standing and easing within 15 to 30 minutes of lying flat; this can become non-orthostatic with time.
• Neck pain or stiffness, nausea, tinnitus, muffled hearing, dizziness, photophobia and interscapular pain.
• Cranial nerve palsies (sixth nerve), cognitive change, gait disturbance or coma from severe brain sagging.
• Headache after exertion, Valsalva manoeuvre or a minor injury.

Red flags.

• Reduced consciousness, confusion or progressive dementia like syndrome.
• Thunderclap headache, focal signs or seizure (subdural haematoma, venous thrombosis, haemorrhage).
• Fever, meningism or recent lumbar puncture or surgery.

• MRI of the brain with gadolinium: pachymeningeal enhancement, brain sagging, venous engorgement, subdural collections and pituitary hyperaemia (the "SEEPS" features); the scan is normal in about 20%.
• MRI of the whole spine with heavily T2-weighted sequences for extradural fluid collections; CT myelography, digital subtraction myelography or dynamic CT myelography to find the leak site or fistula.
• Lumbar puncture is not needed, but low opening pressure (under 6 cmH2O) supports the diagnosis; pressure can be normal in many.
• Assess for connective tissue disorders and risk of venous thrombosis.

Differential diagnosis. Postural orthostatic tachycardia syndrome, cervicogenic headache, chronic migraine, new daily persistent headache, cerebral venous thrombosis, idiopathic intracranial hypertension, post-lumbar-puncture headache and meningitis.

• Conservative care for 1 to 2 weeks: lying flat as tolerated, oral fluids, avoiding straining and heavy lifting.
• Caffeine 200 mg orally twice daily (for example with food). Maximum 400 mg daily. Monitor palpitations, insomnia and anxiety. Avoid in arrhythmia, severe hypertension and pregnancy (limit intake); use caution with anxiety disorders.
• Paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease), for the shortest period that controls pain. Monitor liver function with prolonged use. Reduce dose in hepatic impairment; extend the interval when eGFR is under 30.
• Epidural blood patch for persistent symptoms: 20 mL (up to 30 mL as tolerated) of autologous blood injected into the epidural space, under fluoroscopy or CT imaging, at the leak site if known, or as a non-targeted lumbar patch; repeat if symptoms recur. Maximum 30 mL for each patch. Monitor back pain, radiculopathy, fever and rebound intracranial hypertension. Avoid in coagulopathy, anticoagulation, local or systemic infection and bacteraemia; stop anticoagulants only with specialist advice.
• Fibrin sealant patch, targeted under CT imaging, for those who fail blood patches.
• Surgical repair of a dural tear, or ligation and embolisation of a fistula, at a specialist centre for persistent leaks.
• Treat subdural collections: observe small collections; surgery for large symptomatic haematoma after the leak is addressed.
• Lie flat for 24 hours after a patch, then avoid heavy lifting for 6 weeks.

Monitoring. Review at 1 to 2 weeks and 3 months; repeat MRI if symptoms continue; watch for rebound headache after treatment.

Referral and escalation. Neurology and a specialist neuroradiology centre for investigation; neurosurgery for refractory leaks; urgent admission for reduced consciousness.

Special groups. Pregnancy: conservative care and blood patch are acceptable. Connective tissue disorders: higher recurrence rate.