What is the workup for Idiopathic Intracranial Hypertension (IIH)?

Workup for Idiopathic Intracranial Hypertension (IIH)

The workup for IIH requires urgent MRI brain within 24 hours (or CT if MRI unavailable), followed by mandatory CT/MR venography to exclude cerebral sinus thrombosis, and then lumbar puncture with opening pressure measurement once imaging is normal. 1

Initial Clinical Assessment

Blood Pressure Measurement

• Measure blood pressure immediately to exclude malignant hypertension as a cause of papilledema 1
• Malignant hypertension is defined as diastolic blood pressure >120 mmHg and can mimic IIH 2

Neurological Examination

• Document complete cranial nerve examination, focusing on sixth nerve palsy which may be present in IIH 1
• If cranial nerves other than the sixth nerve are involved, or if other pathological findings exist, strongly consider an alternative diagnosis 1
• Confirm presence and grade of papilledema through ophthalmologic examination 1, 3

Patient Demographics

• Document BMI, as typical IIH patients are female, of childbearing age, with BMI ≥30 kg/m² 3, 2
• Atypical patients (male, not childbearing age, or BMI <30 kg/m²) require more extensive investigation to exclude secondary causes 1, 3

Neuroimaging Protocol

Primary Imaging

• Obtain urgent MRI brain within 24 hours as the first-line imaging modality 1, 3
• If MRI is unavailable within 24 hours, perform urgent CT brain followed by MRI when available 1, 3
• MRI provides superior soft tissue contrast and is particularly valuable in pediatric patients 3

Required Imaging Findings

• Confirm absence of hydrocephalus, mass lesion, structural abnormality, vascular lesion, or abnormal meningeal enhancement 1, 3
• CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis 1
• In non-obese prepubertal children, cerebral venous sinus thrombosis should be particularly considered 3

Supportive Neuroimaging Signs

While not pathognomonic, the following MRI findings support IIH diagnosis:

• Posterior globe flattening (56% sensitivity, 100% specificity) 3
• Intraocular protrusion of the optic nerve (40% sensitivity, 100% specificity) 3
• Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 3
• Enlarged optic nerve sheath (mean 4.3 mm in IIH vs 3.2 mm in controls) 3
• Empty sella or smaller pituitary gland (mean 3.63 mm in IIH vs 5.05 mm in controls) 3
• Transverse sinus stenosis 3, 4

Recent evidence suggests that ≥3 neuroimaging signs have 59.5% sensitivity and 93.5% specificity for IIH diagnosis 4

Lumbar Puncture

Timing and Indications

• Perform lumbar puncture only after normal neuroimaging is confirmed 1
• All patients with papilledema require lumbar puncture to measure opening pressure and analyze CSF contents 1

Proper Technique (Critical to Avoid Misdiagnosis)

• Position patient in lateral decubitus position with legs extended 3
• Ensure patient is relaxed and breathing normally 3
• Measure opening pressure after it stabilizes 3
• Improper positioning (legs flexed, patient tense, or sitting position) will yield falsely elevated readings 3

Diagnostic Thresholds

• Opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) in the lateral decubitus position to meet diagnostic criteria 3
• In children, opening pressure >280 mm CSF is diagnostic; >250 mm CSF in non-sedated, non-obese children 2
• CSF composition must be normal (no pleocytosis, normal protein and glucose) 2

Management of Borderline Pressures

• If opening pressure is borderline (20-24 cm H₂O), arrange close follow-up with repeat lumbar puncture at 2 weeks, as pressure may fluctuate 3
• Consider repeat lumbar puncture if significant deterioration of visual function occurs 3

Common Pitfalls and Caveats

Diagnostic Uncertainty

• When uncertainty exists regarding papilledema versus pseudopapilledema, consult an experienced clinician early before performing invasive tests 1
• IIH without papilledema is a rare subtype that meets all other criteria but lacks papilledema, making diagnosis more challenging 3, 2

Symptom Variability

• Headache phenotype is highly variable and may mimic other primary headache disorders 3
• Common symptoms include progressively severe headache (92%), transient visual obscurations, pulsatile tinnitus, visual blurring, and horizontal diplopia, but none are pathognomonic 3, 5
• Up to 24.7% of patients may be asymptomatic and discovered on routine eye examination 6

Single Measurement Limitation

• Recognize that opening pressure is a single measurement at one point in time; what constitutes "normal" ICP on repeat measurements after initial elevation is unknown 1
• Pressure may fluctuate, requiring clinical judgment and repeat measurements in some cases 3