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ukmla 2026

Idiopathic Intracranial Hypertension

Raised intracranial pressure without a structural cause — classically affecting obese women of childbearing age, presenting with headache, papilloedema, and visual disturbance

Review date
reviewed 2026-04-05
Reading time
6 min read
Author
Dr Kola Tytler MBBS CertHE MBA MSt MRCGP
Neurologyrarechronic
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Condition details
Neurology
rare
6 min read
reviewed 2026-04-05
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About This Page

This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.

Key points

  • Raised ICP without mass lesion, hydrocephalus, or venous sinus thrombosis — diagnosis of exclusion
  • Classic patient: obese woman of childbearing age
  • Key findings: papilloedema on fundoscopy, LP opening pressure >25 cmH2O with normal CSF composition
  • Treatment: weight loss (most important long-term intervention), acetazolamide (carbonic anhydrase inhibitor)
  • Main risk: permanent visual loss from optic nerve compression — requires regular ophthalmology monitoring

Overview

Idiopathic intracranial hypertension (IIH, previously pseudotumour cerebri or benign intracranial hypertension) is a condition of raised intracranial pressure in the absence of mass lesion, hydrocephalus, or venous sinus thrombosis. The pathophysiology is incompletely understood but is strongly associated with obesity — CSF absorption may be impaired. Modified Dandy criteria require: symptoms/signs of raised ICP, papilloedema, normal neuroimaging, normal CSF composition, and elevated LP opening pressure (>25 cmH2O). The term "benign" is no longer used because permanent visual loss occurs in up to 25%.

Epidemiology

IIH has an incidence of approximately 1–2 per 100,000 per year in the general population, but up to 20 per 100,000 in obese women of childbearing age. Over 90% of patients are women. Peak incidence is age 20–44 years. The strongest risk factor is obesity (BMI >30), and recent weight gain is a common precipitant. Medications associated with IIH include tetracyclines, combined oral contraceptive, vitamin A/retinoids, and corticosteroid withdrawal.

Clinical Features

Symptoms
Headache: typically daily, diffuse, worse in the morning, aggravated by coughing/straining/bending
Transient visual obscurations: brief episodes (seconds) of visual loss or dimming, often postural
Pulsatile tinnitus (whooshing sound synchronous with heartbeat)
Diplopia (from sixth nerve palsy — false localising sign of raised ICP)
Progressive visual loss if untreated — the main clinical concern
Nausea
Signs
Papilloedema on fundoscopy — bilateral in most cases. MANDATORY finding for diagnosis
Sixth nerve palsy (abducens): false localising sign of raised ICP — causes lateral rectus weakness and diplopia
Enlarged blind spot on visual field testing
Visual field constriction (peripheral field loss) — indicates optic nerve damage
Obesity — BMI >30 in most patients

Investigations

First-line
FundoscopyESSENTIAL — papilloedema confirms raised ICP. Grade severity (Frisén scale). Optic disc pallor = chronic damage
MRI brain with MRV (MR venography)To exclude mass lesion, hydrocephalus, and cerebral venous sinus thrombosis. IIH may show empty sella, flattened posterior globes, optic nerve sheath distension, transverse sinus stenosis
Lumbar punctureOpening pressure >25 cmH2O (measured in lateral decubitus). Normal CSF composition. Therapeutic LP may temporarily relieve symptoms
Second-line
Formal visual field testing (perimetry)Humphrey visual field — baseline and serial monitoring. Enlarged blind spot, inferonasal loss, peripheral constriction
OCT (optical coherence tomography)Measures retinal nerve fibre layer thickness — monitors for optic nerve damage
Specialist
CT venographyIf MRV unavailable or inconclusive — to exclude venous sinus thrombosis

Management

UK IIH Consensus Guidelines (Mollan et al, JNNP 2018) — no specific NICE guideline
1
Weight management
  • Weight loss is the most important and effective long-term intervention
  • Target: 5–10% body weight loss — associated with significant improvement in papilloedema and symptoms
  • Consider bariatric surgery referral for BMI >40 (or >35 with complications) if medical weight management fails
2
Pharmacological
  • Acetazolamide 250 mg BD, titrated up to 1–2 g/day — reduces CSF production (carbonic anhydrase inhibitor)
  • Side effects: paraesthesiae, fatigue, nausea, taste disturbance, metabolic acidosis, renal stones
  • Topiramate: alternative — also aids weight loss. Teratogenic (avoid in pregnancy)
3
Emergency and surgical interventions
  • Therapeutic lumbar puncture: temporary relief of acute symptoms (e.g. severe visual loss), not a long-term solution
  • Optic nerve sheath fenestration: if acute/severe visual loss threatening sight — protects optic nerve
  • CSF diversion (ventriculoperitoneal or lumboperitoneal shunt): for refractory cases with intractable headache or progressive visual loss
  • Venous sinus stenting: emerging intervention for cases with demonstrated transverse sinus stenosis — specialist centres only
4
Monitoring
  • Regular ophthalmology review: visual fields, fundoscopy, OCT — at least monthly during active disease
  • Visual loss can be insidious and asymptomatic — regular monitoring is critical
  • Withdraw causative medications: tetracyclines, high-dose vitamin A, COC

Complications

  • Permanent visual loss: Up to 25% — from chronic papilloedema causing optic atrophy. Can be sudden (fulminant IIH)
  • Optic atrophy: Irreversible optic nerve damage from chronic compression
  • Medication side effects: Acetazolamide — paraesthesiae, renal stones, metabolic acidosis
  • Chronic headache: May persist even after ICP normalised — consider coexistent migraine
UKMLA Exam Tips
  • 1Obese young woman + headache + papilloedema + normal MRI = think IIH
  • 2LP opening pressure >25 cmH2O with normal CSF composition confirms diagnosis
  • 3Papilloedema is MANDATORY for diagnosis — if no papilloedema, diagnosis is uncertain
  • 4Transient visual obscurations (brief visual dimming) are a warning sign of impending visual loss
  • 5Sixth nerve palsy in IIH is a FALSE LOCALISING SIGN — it does not indicate a pontine lesion
  • 6Weight loss 5–10% is the most effective long-term treatment. Acetazolamide first-line medical therapy
  • 7IIH is NOT benign — permanent visual loss occurs in up to 25%

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Verified Sources & References

Mollan et al — IIH Consensus Guidelines (JNNP, 2018)
NICE CKS — Idiopathic intracranial hypertension
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