What is Idiopathic Intracranial Hypertension?
Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri, is a syndrome of elevated intracranial pressure without an identifiable cause, occurring predominantly in obese women of childbearing age, characterized by papilledema and normal brain imaging. 1
Definition and Core Features
IIH is defined by the combination of:
- Raised intracranial pressure (CSF opening pressure ≥250 mm H₂O in lateral decubitus position) 2
- No hydrocephalus or mass lesion on neuroimaging 1
- Normal cerebrospinal fluid composition 1
- No underlying identifiable etiology 1
- Papilledema as the hallmark finding 2
The condition literally means "false brain tumor" because it mimics the symptoms of a brain tumor without an actual mass being present 3.
Epidemiology and Risk Factors
The typical patient profile is a young, obese woman of childbearing age with BMI >30 kg/m² 2. The overall age-adjusted and gender-adjusted annual incidence is increasing, reported at 2.4 per 100,000 in the last decade (2002-2014) 1. The female-to-male ratio is approximately 7:1 4.
The striking association with obesity is a defining characteristic, though the underlying pathogenesis remains not fully understood 1.
Clinical Presentation
Primary Symptoms
The most common presenting symptoms include:
- Headache (present in nearly 90% of patients): typically progressively more severe and frequent, often holocephalic or unilateral throbbing, worse in the morning after supine positioning and improving with upright posture throughout the day 5, 2
- Transient visual obscurations: unilateral or bilateral darkening of vision lasting seconds 2
- Visual blurring 2
- Pulsatile tinnitus: a whooshing sound synchronous with the pulse 2
- Horizontal diplopia: often due to sixth nerve palsy 5
Additional Symptoms
Other symptoms that may occur include:
- Nausea and vomiting related to elevated intracranial pressure 5
- Dizziness 2
- Neck and back pain 2
- Radicular pain 2
- Cognitive disturbances 2
Important Caveat
None of these symptoms are pathognomonic for IIH, meaning they can occur in other conditions, and the headache phenotype is highly variable and can mimic other primary headache disorders, making clinical diagnosis challenging 2.
Physical Examination Findings
Papilledema is the ophthalmoscopic hallmark of IIH and should be documented 2. However, papilledema may not be detected initially in approximately 21% of patients 4, and unilateral or highly asymmetrical papilledema occurs in less than 4% of patients with definite IIH 6.
Cranial nerve examination typically shows no cranial nerve involvement other than possible sixth nerve palsy/palsies 2. If other cranial nerves or pathological findings are involved, alternative diagnoses should be considered 2.
Diagnostic Approach
Neuroimaging Requirements
The first step is urgent MRI brain within 24 hours; if MRI is unavailable, urgent CT brain should be performed with subsequent MRI if no lesion is identified 2. MRI is the preferred modality because it provides superior soft tissue contrast resolution and is more sensitive for detecting secondary signs of increased intracranial pressure 2.
CT or MR venography is mandatory within 24 hours to exclude cerebral sinus thrombosis 2. Neuroimaging should show no evidence of hydrocephalus, mass, structural or vascular lesion, and no abnormal meningeal enhancement 2.
Key MRI Findings Supporting IIH
Characteristic neuroimaging features include:
- Posterior globe flattening (56% sensitivity, 100% specificity) 5
- Intraocular protrusion of the optic nerve (40% sensitivity, 100% specificity) 5
- Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 5
- Enlarged optic nerve sheath (mean 4.3 mm in IIH vs 3.2 mm in controls) 2
- Empty sella or partially empty sella 5
- Smaller pituitary gland size (mean 3.63 mm in IIH vs 5.05 mm in controls) 2
CSF Analysis
Mandatory measurement of opening CSF pressure is required following normal neuroimaging in all patients with papilledema 2. The CSF opening pressure must be ≥250 mm H₂O measured in the lateral decubitus position with the patient relaxed and legs extended 2. If the opening pressure is 180-250 mm H₂O, close follow-up with repeat lumbar puncture at 2 weeks should be arranged, as pressure may fluctuate 2.
Three Main Treatment Principles
The consensus guidelines identify three fundamental treatment goals 1:
- Treat the underlying disease (weight loss in obese patients)
- Protect the vision (prevent irreversible visual loss from papilledema)
- Minimize headache morbidity
First-Line Treatment
Weight loss is the first-line treatment for overweight patients, while acetazolamide should be initiated as the primary medical therapy for patients with mild visual loss 7. All overweight IIH patients should be encouraged to enter a weight-management program with a goal of 5-10% weight loss, along with a low-salt diet 8.
Surgical Interventions
When there is evidence of declining visual function with pathologically high CSF pressure, immediate surgical intervention is required to preserve vision 2. Options include:
- Ventriculoperitoneal (VP) shunt as the preferred CSF diversion procedure due to lower reported revision rates 7
- Optic Nerve Sheath Fenestration (ONSF) is effective and safe with fewer complications than CSF diversion procedures, but should only be performed by experienced clinicians 7
Medications to Avoid
Medications that might cause or exacerbate IIH should be identified and discontinued if possible, including tetracyclines, vitamin A, retinoids, steroids, growth hormone, thyroxine, and lithium 7.
Prognosis and Monitoring
Treatment failure rates include worsening vision after stabilization in 34% of patients at 1 year and 45% at 3 years 7. Failure to improve headache occurs in one-third to one-half of treated patients 7. If untreated, papilledema can cause progressive irreversible visual loss and optic atrophy 8.