What are the diagnostic criteria and management options for a patient suspected of having idiopathic intracranial hypertension (IIH)?

Diagnostic Criteria for Idiopathic Intracranial Hypertension

The diagnosis of IIH requires urgent MRI brain within 24 hours (or CT if MRI unavailable), followed by lumbar puncture showing opening pressure ≥25 cm H₂O in the lateral decubitus position, with normal CSF contents and no alternative cause identified on imaging. 1, 2

Immediate Diagnostic Steps

Neuroimaging (Within 24 Hours)

• Obtain MRI brain as first-line imaging to exclude hydrocephalus, mass lesions, structural abnormalities, vascular lesions, and abnormal meningeal enhancement 1, 2
• If MRI is unavailable within 24 hours, perform urgent CT brain followed by MRI when available 1, 2
• CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis 1, 2
• MRI provides superior soft tissue contrast and is more sensitive for detecting secondary signs of elevated intracranial pressure, including dilated optic sheaths, tortuous optic nerves, and posterior globe flattening 2

Key MRI Findings Supporting IIH (Not Required but Supportive)

• Posterior globe flattening (56% sensitivity, 100% specificity) 2
• Intraocular protrusion of the optic nerve (40% sensitivity, 100% specificity) 2
• Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 2
• Enlarged optic nerve sheath (mean 4.3 mm in IIH vs 3.2 mm in controls) 2
• Empty sella (most frequent finding, present in nearly all IIH patients) 3
• Increased prepontine AP diameter and larger Meckel cave measurements 3

Lumbar Puncture Requirements

• Perform LP only after normal neuroimaging in all patients with papilledema 1, 2
• Measure opening pressure in the lateral decubitus position with legs extended, patient relaxed and breathing normally 1, 2
• Opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) to meet diagnostic criteria 2
• Wait for pressure to stabilize before recording measurement 2
• CSF contents must be normal (no infection, malignancy, or other abnormality) 1

Common pitfall: If opening pressure is borderline (20-24 cm H₂O) but clinical suspicion remains high, arrange close follow-up with repeat LP at 2 weeks, as pressure may fluctuate and become elevated on subsequent measurements 2

Clinical Examination Findings

Ophthalmologic Assessment (Essential)

• Document papilledema as the hallmark finding—this is present in typical IIH 1, 2
• Perform formal visual field assessment to detect defects (enlarged blind spot, arcuate defects) 2, 4
• Measure visual acuity 2
• Conduct pupil examination 2
• Perform dilated fundal examination to grade papilledema severity 2
• Obtain serial optic nerve head photographs or OCT imaging at initial presentation 2

Important caveat: Papilledema may be asymmetric or even unilateral in IIH—this does not exclude the diagnosis 4. Additionally, IIH without papilledema is a rare subtype that meets all other criteria but lacks papilledema, making diagnosis more challenging 1, 2

Neurological Examination

• Record cranial nerve examination—typically only sixth nerve palsy/palsies should be present 1, 2
• If other cranial nerves are involved or other pathological findings exist, strongly consider alternative diagnoses 1, 2

Patient Characteristics and Risk Stratification

• Calculate BMI and document weight 2
• Typical IIH: Female, childbearing age, BMI ≥30 kg/m² 1, 2
• Atypical IIH: Not female, not of childbearing age, or BMI <30 kg/m²—these patients require more in-depth investigation to exclude secondary causes 1, 2
• Document 5-15% weight gain in the year preceding diagnosis, which is common 2

Clinical Presentation

Primary Symptoms to Assess

• Headache (present in 92% of patients)—progressively more severe and frequent, with highly variable phenotype that may mimic other primary headache disorders 2, 5
• Transient visual obscurations—unilateral or bilateral darkening of vision lasting seconds 2
• Pulsatile tinnitus—whooshing sound synchronous with pulse 2
• Visual blurring 2
• Horizontal diplopia (from sixth nerve palsy) 2

Critical point: None of these symptoms are pathognomonic for IIH, and headache phenotype is highly variable, making clinical diagnosis challenging without objective findings 2

Additional Symptoms

• Dizziness, neck pain, back pain, cognitive disturbances, and radicular pain may occur 2

Classification After Diagnostic Workup

Fulminant IIH

• Precipitous decline in visual function within 4 weeks of diagnosis 1
• Vision is at imminent risk—requires urgent surgical intervention 1, 2

Typical IIH

• Female, childbearing age, BMI ≥30 kg/m² 1, 2
• Most common presentation 5

Atypical IIH

• Does not fit typical demographic profile 1, 2
• Requires more extensive investigation to exclude secondary causes 1, 2
• In non-obese prepubertal children, cerebral venous sinus thrombosis should be particularly considered 2

IIH Without Papilledema

• Rare subtype meeting all IIH criteria except papilledema is absent 1, 2

Diagnostic Pitfalls to Avoid

• Never diagnose IIH without measuring opening pressure—imaging findings alone are insufficient 1, 2
• Do not perform LP before neuroimaging—must exclude mass lesion and venous sinus thrombosis first 1, 2
• Improper LP technique leads to false readings—patient must be in lateral decubitus position with legs extended, relaxed, breathing normally, and pressure must stabilize before measurement 1, 2
• Normal CT does not exclude IIH—many confirmed IIH patients have completely normal CT scans; MRI should still be performed 2
• Absence of papilledema does not exclude increased intracranial pressure—previous long-standing papilledema can induce optic disc changes that prevent further disc swelling 4
• Visual atrophy can mimic regression of papilledema—this represents disease progression, not improvement 4