# Idiopathic Intracranial Hypertension

## Introduction

Idiopathic intracranial hypertension (IIH), formerly known as pseudotumor cerebri, is a syndrome of elevated intracranial pressure without an identifiable structural cause such as a mass lesion, hydrocephalus, or venous sinus thrombosis. It predominantly affects obese women of childbearing age, with an incidence of approximately 1 to 2 per 100,000 in the general population, rising to 20 per 100,000 in obese women. Without treatment, progressive visual loss can lead to permanent blindness.

## Pathophysiology

The exact mechanism of IIH remains incompletely understood. Proposed theories include impaired CSF absorption at the arachnoid granulations, elevated cerebral venous pressure that reduces the CSF-venous pressure gradient, increased CSF production (which is less well supported), and hormonal and metabolic influences related to obesity and adipose tissue. Venous sinus stenosis, particularly of the transverse sinus, is frequently observed on imaging and may be either a cause or a consequence of elevated ICP. Known associations include obesity, vitamin A excess, tetracycline antibiotics, growth hormone therapy, and oral contraceptives.

## Clinical Presentation

Headache is the most common symptom, present in more than 90 percent of patients. It is often daily, diffuse, and worse in the morning or with Valsalva maneuvers. Visual symptoms include transient visual obscurations (brief episodes of vision loss), progressive visual field loss, and diplopia from sixth cranial nerve palsy. Bilateral papilledema, visible as optic disc swelling on fundoscopy, is the hallmark finding. Pulsatile tinnitus, described as a pulse-synchronous whooshing sound, is another characteristic symptom. Neck and back pain may also be present.

![Fundoscopic image showing bilateral papilledema with disc margin blurring and peripapillary hemorrhages](/images/neurosurgery/papilledema-fundoscopy.png)

## Diagnostic Criteria (Modified Dandy Criteria)

The diagnosis of IIH requires five criteria to be met. First, there must be signs and symptoms of elevated intracranial pressure, including headache, papilledema, and visual changes. Second, there should be no localizing neurological signs other than sixth nerve palsy. Third, brain parenchyma must appear normal on neuroimaging, with MRI preferred. Fourth, lumbar puncture must demonstrate an elevated opening pressure above 25 cm H2O in adults, measured in the lateral decubitus position. Fifth, CSF composition must be normal, with normal cell count, protein, and glucose.

### Neuroimaging Findings

MRI of the brain may reveal an empty sella, flattening of the posterior globe, distension of the perioptic subarachnoid space, and tortuosity of the optic nerve. MR venography is essential to rule out cerebral venous sinus thrombosis and may reveal transverse sinus stenosis. There should be no mass lesion or hydrocephalus.

## Ophthalmologic Assessment

Formal perimetry using Humphrey visual fields is critical for monitoring disease progression and treatment response. The most common visual field defect is an enlarged blind spot, followed by inferonasal loss. Optical coherence tomography (OCT) provides quantitative measurement of retinal nerve fiber layer thickness. Serial visual field testing determines whether the disease is progressing or responding to treatment.

![MRI showing empty sella and flattened posterior globe in idiopathic intracranial hypertension](/images/neurosurgery/iih-mri-findings.png)

## Medical Management

Weight loss of 5 to 10 percent of body weight can significantly lower ICP and improve symptoms, and it remains the only intervention shown to produce long-term disease remission. Acetazolamide is the first-line pharmacotherapy. As a carbonic anhydrase inhibitor, it reduces CSF production at typical doses of 500 to 2000 mg/day. Topiramate is an alternative agent with the dual benefit of ICP reduction and weight loss. Furosemide serves as an adjunctive diuretic therapy. Serial lumbar punctures provide temporary relief but are not a sustainable long-term strategy. The IIHTT (IIH Treatment Trial) demonstrated that acetazolamide combined with a weight management program improved visual field function and papilledema grade.

## Surgical Management

### Optic Nerve Sheath Fenestration (ONSF)

ONSF is indicated for progressive visual loss despite maximal medical therapy. The procedure creates a window in the optic nerve sheath to decompress the perioptic subarachnoid space. It primarily protects vision but may not reliably treat headache. Risks include visual deterioration, diplopia, and pupillary dysfunction.

### CSF Diversion Procedures

VP shunts and LP shunts are effective for both headache and visual symptoms. LP shunts were historically preferred in IIH but have higher revision rates. VP shunts with programmable valves allow postoperative pressure adjustments. Shunt complication and revision rates remain significant, at 40 to 60 percent within two years.

### Venous Sinus Stenting

Venous sinus stenting is an emerging treatment for patients with documented transverse sinus stenosis and a significant pressure gradient exceeding 8 mmHg. The procedure involves endovascular placement of a stent to relieve venous outflow obstruction. Early results are promising, with improvement in headache, papilledema, and ICP. However, long-term data and randomized trials remain limited, and lifelong antiplatelet therapy is required after stenting.

| Procedure | Primary Benefit | Best Indication | Key Limitation |
|-----------|----------------|-----------------|----------------|
| ONSF | Vision protection | Progressive visual loss; headache not primary concern | May not improve headache |
| VP shunt | Headache + vision | Generalized symptoms; failed medical therapy | 40-60% revision rate at 2 yr |
| LP shunt | Headache + vision | Historically preferred in IIH | Higher revision rate than VP |
| Venous sinus stenting | ICP reduction + headache + vision | Documented stenosis with gradient >8 mmHg | Limited long-term data; lifelong antiplatelet |

![Cerebral venogram demonstrating bilateral transverse sinus stenosis with pressure gradient measurement](/images/neurosurgery/venous-sinus-stenosis-iih.png)

## Clinical Pearls

IIH is a diagnosis of exclusion, and venous sinus thrombosis must always be ruled out with MR venography before making the diagnosis. Visual loss, not headache, is the primary indication for surgical intervention. Every patient with IIH requires serial ophthalmologic monitoring with formal visual field testing to detect progressive visual loss. Weight loss remains the only intervention shown to produce long-term disease remission. Fulminant IIH with rapid visual deterioration is a neurosurgical emergency requiring urgent CSF diversion or optic nerve sheath fenestration.

## References

1. Friedman DI, Liu GT, Digre KB. Revised diagnostic criteria for the pseudotumor cerebri syndrome in adults and children. *Neurology*. 2013;81(13):1159-1165.
2. Wall M, McDermott MP, Kieburtz KD, et al. Effect of acetazolamide on visual function in patients with idiopathic intracranial hypertension and mild visual loss: the IIHTT. *JAMA*. 2014;311(16):1641-1651.
3. Dinkin MJ, Patsalides A. Venous sinus stenting in idiopathic intracranial hypertension: results of a prospective trial. *Journal of Neuro-Ophthalmology*. 2017;37(2):113-121.
4. Mollan SP, Davies B, Silver NC, et al. Idiopathic intracranial hypertension: consensus guidelines on management. *Journal of Neurology, Neurosurgery & Psychiatry*. 2018;89(10):1088-1100.