What are the diagnostic criteria for Idiopathic Intracranial Hypertension (IIH)?

Diagnostic Criteria for Idiopathic Intracranial Hypertension

IIH is diagnosed using the modified Dandy criteria, which require: (1) signs and symptoms of elevated intracranial pressure, (2) papilledema on examination, (3) elevated CSF opening pressure ≥25 cm H₂O measured in lateral decubitus position, (4) normal CSF composition, and (5) neuroimaging showing no hydrocephalus, mass, structural/vascular lesion, or abnormal meningeal enhancement. 1

Required Clinical Features

Symptoms of Elevated Intracranial Pressure

• Headache that is progressively more severe and frequent is the most common presenting symptom 1
• Transient visual obscurations (unilateral or bilateral darkening of vision lasting seconds) 1
• Pulsatile tinnitus (whooshing sound synchronous with pulse) 1
• Visual blurring 1
• Horizontal diplopia 1
• Additional symptoms may include dizziness, neck pain, back pain, cognitive disturbances, and radicular pain 2
• None of these symptoms are pathognomonic for IIH, and the headache phenotype is highly variable, potentially mimicking other primary headache disorders 1

Physical Examination Findings

• Papilledema is the hallmark finding and must be documented 1
• Bilateral papilledema is present in approximately 82% of patients 3
• Sixth cranial nerve palsy (unilateral or bilateral) may be present 1, 4
• No other cranial nerve involvement should be present; if other cranial nerves are affected, alternative diagnoses must be considered 1

Mandatory Diagnostic Testing

Neuroimaging Requirements

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

Supportive MRI Findings (Not Required for Diagnosis)

• Posterior globe flattening (56% sensitivity, 100% specificity) 1
• Intraocular protrusion of the optic nerve (40% sensitivity, 100% specificity) 1
• Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 1
• Enlarged optic nerve sheath (mean 4.3 mm in IIH vs 3.2 mm in controls) 1
• Smaller pituitary gland size (mean 3.63 mm in IIH vs 5.05 mm in controls) 1
• Empty or partially empty sella, transverse sinus stenosis 2

Lumbar Puncture Requirements

• CSF opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) measured in the lateral decubitus position 1
• Proper technique is essential: patient must be in lateral decubitus position, legs extended, relaxed, breathing normally, with measurement taken after pressure stabilizes 1
• CSF composition must be normal 1, 5
• If opening pressure is <25 cm H₂O but clinical suspicion remains high, arrange close follow-up with repeat lumbar puncture at 2 weeks, as pressure may fluctuate 1

Typical Patient Profile

• Female sex, childbearing age, BMI >30 kg/m² defines the typical IIH patient 1, 6
• Approximately 72% of patients have BMI above normal range 3
• Atypical patients (male, normal weight, outside childbearing age) require more in-depth investigation 1
• Male patients tend to have lower BMI, lower incidence of headache, and increased visual impairment 3

Important Diagnostic Pitfalls

IIH Without Papilledema

• This is a rare subtype that meets all other criteria for IIH but lacks papilledema, making diagnosis more difficult 1, 2

Pediatric Considerations

• In non-obese prepubertal children, cerebral venous sinus thrombosis should be particularly considered as a cause of secondary pseudotumor cerebri, making venography especially important in this population 1

Measurement Errors

• Improper positioning during lumbar puncture (patient not relaxed, legs not extended, not in lateral decubitus) can lead to falsely elevated or normal readings and misdiagnosis 1