What is the recommended workup for a suspected case of Idiopathic Intracranial Hypertension (IIH) in an obese woman of childbearing age presenting with headaches and vision changes?

Workup for Idiopathic Intracranial Hypertension

Immediate Neuroimaging (Within 24 Hours)

Obtain urgent MRI brain within 24 hours as the first diagnostic step; if MRI is unavailable within this timeframe, perform urgent CT brain followed by MRI when available. 1, 2

• MRI is the preferred initial test due to superior soft tissue contrast resolution and better detection of subtle secondary signs of elevated intracranial pressure 2
• Neuroimaging must exclude hydrocephalus, mass lesions, structural or vascular abnormalities, and abnormal meningeal enhancement 1
• CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis 1, 2

Key MRI Findings Supporting IIH (Not Required for Diagnosis)

• 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 vs 3.2 mm in controls) 2
• Empty sella and smaller pituitary gland size 2, 3

Lumbar Puncture with Opening Pressure

Following normal neuroimaging, all patients with papilledema must undergo lumbar puncture to measure opening pressure and analyze CSF contents. 1, 2

Proper Measurement Technique

• Patient must be in lateral decubitus position with legs extended, relaxed, and breathing normally 2
• Measure after pressure stabilizes 2
• Opening pressure ≥25 cm H₂O (≥250 mm H₂O) is required to meet diagnostic criteria 2

Important Caveat

If opening pressure is borderline or normal but clinical suspicion remains high, arrange close follow-up with repeat lumbar puncture at 2 weeks, as pressure may fluctuate and become elevated on subsequent measurements 2

Clinical Examination

Ophthalmologic Assessment

Document the following at initial presentation: 1

• Visual acuity
• Pupil examination
• Formal visual field assessment (perimetry)
• Dilated fundal examination to grade papilledema severity
• Serial optic nerve head photographs or OCT imaging 1

Neurologic Examination

• Assess for papilledema (hallmark finding) 1, 2
• Cranial nerve examination: typically only sixth nerve palsy/palsies may be present 1
• If other cranial nerves are involved or other pathological findings exist, consider alternative diagnoses 1

Additional Baseline Assessments

Demographic and Anthropometric Data

• Calculate BMI to classify as typical IIH (female, reproductive age, BMI ≥30 kg/m²) versus atypical IIH 1, 2
• Document weight, as 5-15% weight gain in the year preceding diagnosis is common 1

Blood Pressure Measurement

• Mandatory to exclude malignant hypertension as a cause of papilledema 4

Headache Characterization

• Document headache features, frequency, and severity 1
• Assess frequency of analgesic use 1
• Consider validated headache disability score such as HIT-6 1

Common Pitfalls to Avoid

• Do not rely on CT alone: A normal CT does not exclude IIH, as many confirmed cases have completely normal CT scans; MRI must still be performed 2
• Do not dismiss borderline opening pressures: Pressure fluctuates, and repeat measurement may be necessary 2
• Do not assume all headaches are from elevated ICP: Headache phenotype is highly variable and may mimic other primary headache disorders, making clinical diagnosis challenging 2
• Do not overlook IIH without papilledema: This rare subtype meets all other criteria but lacks papilledema, making diagnosis more difficult 2

Classification After Workup

Based on workup results, classify the patient as: 1

• Fulminant IIH: Vision at imminent risk requiring urgent intervention
• Typical IIH: Female, reproductive age, BMI ≥30 kg/m²
• Atypical IIH: Does not fit typical demographic profile (requires more in-depth investigation for secondary causes)