Idiopathic Intracranial Hypertension (IIH)
Summary
Idiopathic Intracranial Hypertension (IIH) is a condition of raised intracranial pressure (ICP) of unknown aetiology, predominantly affecting obese women of childbearing age. The historical term "Benign" is obsolete because it carries a high risk of permanent blindness. The classic presentation is headache (worse on lying flat/Valsalva), transient visual obscurations, and pulsatile tinnitus. Examination reveals Papilloedema and occasionally a VIth nerve palsy. Diagnosis requires satisfying the Modified Dandy Criteria: Signs of raised ICP, Normal MRI/MRV (excluding thrombosis), and Opening Pressure >25 cmH2O on Lumbar Puncture. Management is urgent preservation of vision. Weight loss is the only disease-modifying therapy. Acetazolamide reduces CSF production. Surgical interventions (Shunts, Stenting, Fenestration) are reserved for threatened vision or intractable headache. [1,2]
Key Facts
- Epidemiology: 90% are obese women (BMI >30). Incidence is rising with the obesity epidemic.
- Pathophysiology: Controversy exists. Likely a mismatch between CSF production and resorption, possibly driven by venous sinus stenosis (transverse sinus).
- Vision is Key: Headache is the symptom, but Blindness is the outcome. Regular visual fields are mandatory.
- The "Stenosis" Debate: Venous Sinus Stenosis is common. Is it the cause (obstruction) or the effect (compression by high ICP)? Recent evidence suggests stenting can cure it.
- Secondary Causes: Tetracyclines, Retinoids (Vit A), Steroid withdrawal, Addisons, OSA.
Clinical Pearls
"The Whooshing Sound": Pulsatile tinnitus (hearing one's heartbeat) is a highly specific symptom for raised ICP. It often stops if the patient compresses their jugular vein.
"Transient Visual Obscurations (TVOs)": Grey-outs of vision lasting seconds, triggered by bending over or standing up. They indicate optic nerve head ischaemia/congestion.
"The Empty Sella": A common MRI finding in IIH. The high pressure flattens the pituitary gland against the floor of the sella turcica.
"Don't Miss the Thrombus": A Cerebral Venous Sinus Thrombosis (CVST) mimics IIH perfectly. You MUST request an MRV (Venogram), not just an MRI.
Incidence
- General Population: 1-2 per 100,000.
- Obese Women (20-44y): 20 per 100,000.
- Paediatric IIH: Rare. Affects boys and girls equally. Often not associated with obesity.
The "Monro-Kellie" Imbalance
The skull is a fixed box containing Brain, Blood, and CSF. In IIH, the CSF volume/pressure is high. Why?
- CSF Resorption Failure: Arachnoid granulations fail to drain CSF into the venous sinuses.
- Venous Hypertension: High central venous pressure (due to obesity/abdominal pressure) is transmitted to the intracranial veins, reducing the gradient for drainage.
- Transverse Sinus Stenosis: Seen in >90%. It creates a pressure gradient. Stenting it can normalize ICP.
- Hormonal/Metabolic: A link to Adipokines/Vitamin A metabolism? (Retinol increases CSF production).
Symptoms
- Headache (90%):
- Daily, dull, global.
- Worsened by Valsalva (Coughing, Straining) and Recumbency (Morning headache).
- Visual Obscurations (TVOs) (70%):
- Brief (<30s) greying out of vision.
- Binocular or monocular.
- Precipitated by posture change.
- Pulsatile Tinnitus (60%):
- "Whooshing" or "Heartbeat" in the ear.
- Unilateral or Bilateral.
- Diplopia:
- Horizontal diplopia.
- Due to VI nerve (Abducens) palsy - a "false localising sign" caused by stretching of the nerve.
Signs
- Papilloedema:
- Swollen optic discs.
- Blurring of margins.
- Haemorrhages (Splinter).
- Paton's Lines (Retinal folds).
- Note: In chronic IIH, the disc becomes pale (Optic Atrophy) - a sign of permanent damage.
- Visual Field Defect:
- Enlarged Blind Spot (earliest sign).
- Constriction of peripheral field.
- Nasal step.
- Sixth Nerve Palsy: Failure of abduction.
Imaging (MRI + MRV)
Mandatory rule-out of structural cause.
- MRI Brain:
- Normal brain parenchyma (No tumour).
- Signs of High Pressure:
- Empty Sella (70%).
- Flattening of posterior globe (Posterior Sclera).
- Distension of optic nerve sheath.
- Tortuous optic nerve.
- MR Venogram (MRV):
- Rule out Sinus Thrombosis.
- Look for Transverse Sinus Stenosis.
Lumbar Puncture (LP)
The Diagnostic Test.
- Opening Pressure:
- Must be measured in Lateral Decubitus position with legs extended (relaxed).
- > 25 cmH2O: Diagnostic for IIH.
- 20-25: Equivocal.
- < 20: Normal.
- CSF Analysis: Normal protein/glucose/cells.
Ophthalmology Review
- Visual Fields (Humphrey): Mandatory baseline and monitoring.
- OCT: Quantifies papilloedema thickness.
Management Algorithm
DIAGNOSIS CONFIRMED
↓
┌───────────┴───────────────┐
VISION VISION VISION
STABLE THREATENED LOST/SEVERE
↓ ↓ ↓
- Weight Loss - High Dose ACZ - EMERGENCY
- Acetazolamide- Topiramate - SURGERY
- Headache - Consider (Shunt/ONSF)
mgmt Surgery
1. Medical Management
- Weight Loss: The only curative treatment. Loss of 5-10% body weight often induces remission. GLP-1 agonists (Semaglutide) are showing promise.
- Acetazolamide (Diamox):
- Carbonic Anhydrase Inhibitor. reduces CSF production.
- Dose: High! 500mg BD up to 4g daily.
- Side Effects: Paraesthesia (fingers/toes), Metallic taste (fizzy drinks), Acidosis, Kidney stones.
- Topiramate: Weak CA inhibitor + Weight loss benefit + Migraine prophylaxis. Good alternative.
- Furosemide: Weak evidence. Used as adjunct.
2. Surgical Management
Indications: Fulminant IIH (Vision failing rapidly), Failure of medical therapy.
- CSF Diversion (Shunt):
- Ventriculo-Peritoneal (VP) or Lumbo-Peritoneal (LP) shunt.
- Effect: rapid pressure drop.
- Problem: High failure rate (blockage/infection) and "Low Pressure Headache".
- Optic Nerve Sheath Fenestration (ONSF):
- Slits cut into the nerve sheath to relieve pressure locally.
- Saves vision but does NOT cure headache.
- Venous Sinus Stenting:
- Newer procedure. Stenting the transverse sinus stenosis.
- Outcomes: Excellent for pressure and headache. Lower revision rate than shunts. Requires a gradient >8mmHg.
3. Deep Dive: Venous Sinus Stenosis - Cause or Effect?
"The Chicken and Egg."
- The Finding: >90% of IIH patients have stenosis of the Transverse Sinus on MRV.
- Hypothesis A (The Effect): High Intracranial Pressure compresses the sinus (which is a soft tube). The stenosis is a result of the disease.
- Evidence: Doing an LP to lower pressure often resolves the stenosis temporarily.
- Hypothesis B (The Cause): The stenosis creates a "dam", preventing CSF drainage. This causes the high pressure.
- Evidence: Stenting the stenosis cures the disease in many cases.
- The Consensus: It is likely a vicious cycle. A small stenosis raises pressure -> High pressure compresses the sinus further -> More stenosis -> Higher pressure.
4. Surgical Atlas: Stenting vs Shunting
A. Venous Sinus Stenting
- Procedure: Endovascular (Interventional Neuroradiology). Access via femoral vein. Deployment of a self-expanding stent into the transverse sinus.
- Pros: Minimally invasive. Cures the pressure gradient. Solves the "whooshing" noise immediately.
- Cons: Requires dual antiplatelets. Risk of haemorrhage. Failure rate (stent thrombosis).
B. Ventriculo-Peritoneal (VP) Shunt
- Procedure: Neurosurgical hole in skull -> Tube into ventricle -> Tunneled to abdomen.
- Pros: Guaranteed pressure reduction.
- Cons: High Failure Rate. The ventricles in IIH are usually small ("Slit Ventricles"), making placement hard. Shunts often block or over-drain (causing low pressure headaches). 50% require revision within 2 years.
- Cerebral Venous Sinus Thrombosis (CVST): The "Can't Miss" diagnosis.
- Space Occupying Lesion: Tumour/Abscess.
- Meningitis: Chronic (TB/Fungal).
- Malignant Hypertension: Check BP!
- Medication Induced: Tetracyclines (Doxycycline/Minocycline), Vitamin A (Isotretinoin), Growth Hormone.
- Vision: 10-25% suffer permanent visual loss.
- Recurrence: Can recur if weight is regained.
- Headache: Can persist even after papilloedema resolves (Chronic Migraine phenotype).
- IIH Treatment Trial (IIHTT): Confirmed efficacy of Acetazolamide + Weight loss vs Placebo.
What is IIH?
It is a condition where the fluid pressure around your brain is too high. It mimics a brain tumour (hence the old name "Pseudotumor"), but there is no tumour.
Why me?
We don't know exactly, but it is strongly linked to weight. Hormones may play a role.
Is it dangerous?
It is not life-threatening, but it is sight-threatening. The pressure squeezes the optic nerves and can cause blindness if untreated.
What is the treatment?
The most effective treatment is Weight Loss. Losing 10% of your body weight can put the disease into permanent remission. We also use water tablets (Acetazolamide) to lower the pressure.
- Mollan SP, et al. Idiopathic intracranial hypertension: consensus guidelines on management. J Neurol Neurosurg Psychiatry. 2018;89:1088-1100.
- Wall M. Idiopathic Intracranial Hypertension. Neurol Clin. 2010;28:593-617.
Common Exam Questions
1. Pharmacology:
- Q: What is the mechanism of Acetazolamide?
- A: It inhibits Carbonic Anhydrase in the Choroid Plexus, reducing the transport of bicarbonate and sodium, and thus water, into the CSF space.
2. Anatomy:
- Q: Which cranial nerve is most commonly affected and why?
- A: The VIth (Abducens). It has the longest intracranial course and is tethered at Dorello's canal, making it susceptible to stretching by raised ICP.
3. Imaging:
- Q: What is the "Empty Sella" sign?
- A: Herniation of the subarachnoid space into the sella turcica, flattening the pituitary gland. It is a radiological sign of chronically raised ICP.
For Definite IIH Diagnosis:
- Signs/Symptoms: Symptoms of raised ICP or Papilloedema.
- Neurology: No localising signs (except VI nerve palsy).
- Imaging: Normal MRI/CT (No mass, no thrombosis).
- Pressure: Opening Pressure >25 cmH2O (Adults) or >28 cmH2O (Children).
- Biochemistry: Normal CSF composition.
Note: "IIH without Papilloedema" (IIHWOP) exists but is controversial. Requires strict criteria (Pressure >25 + VI nerve palsy OR Stenosis on MRV).
"Just lose weight."
- The Problem: Doctors often treat IIH patients dismissively, attributing the disease solely to "lifestyle". This leads to disengagement and poor outcomes.
- The Reality: Obesity is a complex metabolic disease, not just "willpower".
- The Approach:
- Don't just say "Lose weight". Refer to bariatric services.
- Acknowledge the pain. Headache makes it hard to exercise. Depression is a comorbidity.
- Treat the condition medically while weight loss is in progress.
Advanced Viva Questions
1. Radiology:
- Q: What are the radiological features of raised ICP?
- A: Empty Sella, Tortuous Optic Nerves, Flattening of the posterior globe, Distension of the perioptic subarachnoid space.
2. Pharmacology:
- Q: Why do we use Acetazolamide and not Furosemide?
- A: Acetazolamide directly targets CSF production at the Choroid Plexus (Carbonic Anhydrase dependent). Furosemide is a loop diuretic and has minimal effect on CSF.
3. Surgery:
- Q: What is the main complication of ONSF?
- A: Blindness (due to central retinal artery occlusion or nerve damage) and Diplopia. It also fails to treat the headache in many cases.
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