What investigations should be done in a suspected case of Idiopathic Intracranial Hypertension (IIH) in an obese woman of childbearing age presenting with headache, vision changes, or papilledema?

Investigations in Suspected IIH

All patients with suspected IIH require urgent MRI brain within 24 hours (or CT brain if MRI unavailable, followed by MRI), mandatory CT or MR venography within 24 hours to exclude cerebral sinus thrombosis, and lumbar puncture with opening pressure measurement in the lateral decubitus position after normal imaging is confirmed. 1

Initial Clinical Assessment

Blood Pressure Measurement

• Measure blood pressure immediately to exclude malignant hypertension (diastolic BP >120 mmHg), which can cause papilledema and mimic IIH 1, 2

Neurological Examination

• Document complete cranial nerve examination - in typical IIH, there should be no cranial nerve involvement except possible sixth nerve palsy 1
• If other cranial nerves are involved or other pathological findings are present, strongly consider alternative diagnoses 1
• Record fundoscopic findings to document papilledema grade 1

Patient Classification

• Determine if patient is "typical" (female, childbearing age, BMI ≥30 kg/m²) or "atypical" - atypical patients require more extensive investigation to exclude secondary causes 1

Urgent Neuroimaging (Within 24 Hours)

Primary Brain Imaging

• MRI brain is the preferred initial test - superior soft tissue contrast and more sensitive for detecting secondary signs of elevated intracranial pressure 3
• If MRI unavailable within 24 hours, perform urgent CT brain, then obtain MRI subsequently if CT shows no lesion 1
• Imaging must exclude: hydrocephalus, mass lesions, structural lesions, vascular lesions, and abnormal meningeal enhancement 1

Mandatory Venous Imaging

• CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis - this is non-negotiable regardless of patient presentation 1
• In non-obese prepubertal children, cerebral venous sinus thrombosis is particularly important to exclude 3

Supportive MRI Findings (Not Diagnostic but Suggestive)

• Posterior globe flattening (56% sensitivity, 100% specificity) 3
• Intraocular protrusion of optic nerve (40% sensitivity, 100% specificity) 3
• Horizontal tortuosity of optic nerve (68% sensitivity, 83% specificity) 3
• Enlarged optic nerve sheath (mean 4.3 mm vs 3.2 mm in controls) 3
• Empty sella or smaller pituitary gland (mean 3.63 mm vs 5.05 mm in controls) 3
• These findings support but do not confirm IIH diagnosis 3

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 ensure CSF contents are normal 1

Proper Technique (Critical to Avoid Misdiagnosis)

• Patient must be in lateral decubitus position 1
• Legs must be extended (not flexed) 3
• Patient must be relaxed and breathing normally 3
• Measure after pressure stabilizes 3
• Improper technique leads to falsely elevated readings and misdiagnosis 3

Diagnostic Criteria

• Opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) in adults 3
• CSF composition must be normal - abnormal CSF suggests alternative diagnosis 2
• 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

Ophthalmologic Assessment

Visual Function Testing

• Formal visual field testing is mandatory to document baseline visual function and guide treatment urgency 4
• Document papilledema grade - severe papilledema is a negative prognostic factor and requires more aggressive monitoring 5
• Visual acuity testing 4

Common Pitfalls to Avoid

Diagnostic Uncertainty

• If uncertain about papilledema vs pseudopapilledema, consult an experienced clinician early before performing invasive tests 1
• Do not assume normal CT excludes IIH - many confirmed IIH patients have completely normal CT scans; MRI is still required 3

Atypical Presentations

• Atypical patients (male, not childbearing age, BMI <30 kg/m²) require more extensive investigation to exclude secondary causes 1
• Be aware that IIH can rarely present with isolated facial nerve palsy, though this should prompt careful exclusion of other diagnoses 6

Technical Errors

• Improper lumbar puncture positioning is a frequent cause of diagnostic error - ensure proper lateral decubitus position with legs extended 3
• Do not skip venography - cerebral venous sinus thrombosis must be excluded in all cases 1