What is the diagnostic workup for idiopathic intracranial hypertension (IIH) and its prevalence in teenagers?

Diagnostic Workup of Idiopathic Intracranial Hypertension

The diagnostic workup for IIH requires urgent neuroimaging (MRI brain preferred, or CT if MRI unavailable within 24 hours), followed by mandatory venography (CT or MR venography) to exclude cerebral sinus thrombosis, lumbar puncture with opening pressure measurement ≥25 cm H₂O in lateral decubitus position, and comprehensive neuro-ophthalmological examination documenting papilledema. 1

Initial Imaging Requirements

Neuroimaging must be completed within 24 hours of presentation:

• MRI brain with orbits is the preferred initial test to exclude secondary causes of raised intracranial pressure, including mass lesions, hydrocephalus, structural or vascular lesions, and abnormal meningeal enhancement 1
• If MRI is unavailable within 24 hours, perform urgent CT brain, then obtain MRI subsequently if no lesion is identified 1
• MRI provides superior soft tissue contrast resolution compared to CT and is particularly valuable in pediatric patients 2

Venography is mandatory within 24 hours (CT venography or MR venography) to exclude cerebral venous sinus thrombosis, which can cause secondary pseudotumor cerebri 1, 3

Key MRI Findings Supporting IIH Diagnosis

When MRI brain and orbits is performed, look for these specific neuroimaging signs of elevated intracranial pressure 2, 3:

• 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 in IIH versus 3.2 mm in controls) 2
• Empty or partially empty sella 3
• Transverse sinus stenosis 3
• Smaller pituitary gland size (mean 3.63 mm in IIH versus 5.05 mm in controls) 2

A diagnostic criterion of ≥3 neuroimaging signs has 59.5% sensitivity and 93.5% specificity for IIH 4

Lumbar Puncture Requirements

CSF opening pressure must be ≥25 cm H₂O (≥250 mm H₂O) measured in the lateral decubitus position to meet diagnostic criteria 1

Critical technical requirements for accurate measurement 1:

• Patient must be in lateral decubitus position
• Patient must be relaxed with legs extended
• Proper positioning is essential as pressure can fluctuate

If initial 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 and become elevated on subsequent measurements 1

CSF composition must be normal (no abnormal cells, protein, or glucose) 3

Neuro-Ophthalmological Examination

All patients require thorough documentation of 5:

• Visual acuity testing
• Pupil examination
• Formal visual field assessment (not just confrontation testing)
• Dilated fundal examination to grade papilledema (papilledema is the hallmark finding) 1

Cranial nerve examination should show no cranial nerve involvement except possible sixth nerve palsy 1. Note that while abducens nerve palsy was proposed as a diagnostic criterion, it has been shown to have no diagnostic significance 4

Mandatory Exclusion Criteria

Blood pressure measurement is mandatory to exclude malignant hypertension as a cause of papilledema 3

Neuroimaging must show no evidence of 1:

• Hydrocephalus
• Mass lesions
• Structural or vascular lesions
• Abnormal meningeal enhancement

Common Diagnostic Pitfalls

Headache phenotype in IIH is highly variable and may mimic other primary headache disorders, making clinical diagnosis challenging 1. The headache is typically progressively more severe and frequent, but this is not pathognomonic 1

IIH without papilledema is a rare subtype that meets all other criteria but lacks papilledema, making diagnosis more difficult 1. This requires elevated opening pressure ≥25 cm H₂O with normal neuroimaging and no other identifiable cause 3

Atypical patients (not female, not childbearing age, not obese) require more in-depth investigation as they do not fit the typical demographic profile 1

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Prevalence in Teenagers

IIH can occur in prepubertal thin girls and boys, though it most commonly affects overweight females of childbearing age 3. The condition can affect obese males and prepubertal children of both sexes 3

The incidence of IIH is rising in parallel with the obesity epidemic, which particularly impacts adolescent populations 3, 6. In pediatric patients, elevated opening pressure criteria differ: >280 mm CSF in children or >250 mm CSF in non-sedated, non-obese children 3

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 2