What are the diagnostic criteria for idiopathic intracranial hypertension (IIH)?

Diagnostic Criteria for Idiopathic Intracranial Hypertension

Idiopathic intracranial hypertension (IIH) is diagnosed when a patient has papilledema, elevated CSF opening pressure ≥25 cm H₂O (≥250 mm H₂O) measured in the lateral decubitus position, normal neuroimaging excluding secondary causes, and normal CSF composition. 1

Core Diagnostic Requirements

The diagnosis requires meeting all of the following criteria:

1. Clinical Presentation

• Papilledema is the hallmark finding and must be documented on fundoscopic examination 1
• Symptoms typically include progressively worsening headache, transient visual obscurations (brief bilateral darkening of vision lasting seconds), pulsatile tinnitus, visual blurring, and horizontal diplopia 1, 2
• Sixth nerve palsy causing horizontal diplopia may be present, but involvement of other cranial nerves should prompt consideration of alternative diagnoses 1

2. Elevated Intracranial Pressure

• CSF opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) measured via lumbar puncture in the lateral decubitus position 1
• The patient must be relaxed with legs extended during measurement to ensure accuracy 1
• Important caveat: If initial pressure is borderline or normal but clinical suspicion remains high, arrange repeat lumbar puncture at 2 weeks, as pressure may fluctuate 1
• CSF composition must be normal; abnormal CSF suggests alternative diagnoses 3

3. Neuroimaging Exclusion Criteria

• MRI brain is the preferred initial test and should be performed within 24 hours 1
• If MRI is unavailable within 24 hours, perform urgent CT brain followed by MRI when available 1
• Imaging must show no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement 1
• CT or MR venography is mandatory within 24 hours to exclude cerebral venous sinus thrombosis 1, 2

Supportive Neuroimaging Findings

While not required for diagnosis, the following MRI findings support the diagnosis of IIH:

• Empty or partially empty sella 2
• Perioptic nerve sheath distension (69.8% sensitivity) 4
• Flattening of the posterior globe/sclera (67.1% sensitivity) 4
• Transverse sinus stenosis (60.2% sensitivity) 4
• Moderate suprasellar herniation (71.4% sensitivity) 4
• Increased optic nerve tortuosity 2
• Intraocular protrusion of optic nerve head 2

A recent evidence-based proposal suggests that IIH can be diagnosed with two out of three objective findings: papilledema, opening pressure ≥25 cm CSF, and ≥3 neuroimaging signs (sensitivity 59.5%, specificity 93.5%). 4

Special Diagnostic Scenarios

IIH Without Papilledema

• This is a rare subtype that meets all other criteria for IIH but lacks papilledema 1, 2
• Diagnosis is more challenging and requires heightened clinical suspicion 1
• Even with normal CSF pressure on initial measurement, if papilledema is present with related symptoms, suspicion should remain high as untreated papilledema causes progressive irreversible visual loss 5

Atypical Presentations

• Typical IIH patients are female, of childbearing age, with BMI >30 kg/m² 1, 2
• Atypical patients (male, normal weight, older age) require more in-depth investigation to exclude secondary causes 1

Critical Pitfalls to Avoid

• Do not exclude IIH based solely on normal initial CSF pressure—pressure fluctuates and may be elevated on repeat measurement 1, 5
• Do not rely on symptoms alone—headache phenotype is highly variable and mimics other primary headache disorders 1, 3
• Do not assume abducens nerve palsy is diagnostic—it has no diagnostic significance for IIH 4
• Do not overlook medication history—tetracyclines, vitamin A, retinoids, steroids, growth hormone, thyroxine, and lithium can cause secondary intracranial hypertension 3
• Do not skip venography—cerebral venous sinus thrombosis presents identically to IIH and must be excluded 3