Idiopathic intracranial hypertension (IIH) is a condition characterized by elevated intracranial pressure (ICP) in the absence of parenchymal brain lesions, vascular malformations, hydrocephalus, or CNS infection. Diagnosing IIH in children requires an elevated opening pressure above 28 cmH2O, unless they are not sedated or obese, in which case 25 cmH2O is the accepted level. This article delves into the relationship between venous sinus stenosis, cerebral hemodynamics, and weight loss, particularly in the context of IIH.
Understanding the Pathophysiology of IIH
Early theories regarding the pathogenesis of IIH suggested an increase in the CSF formation rate, an increase in the CSF outflow resistance, or an increase in the venous pressure. However, the literature indicates the first two variables in both equations are found to be associated with active hydrocephalus rather than IIH.
The pressure gradient between the CSF and sagittal sinus is normally around 2.34 mmHg in adults with IIH. Therefore, the elevation in ICP in IIH can only be due to an elevated venous pressure. Venous pressure depends on central venous pressure, venous outflow resistance, and the total blood flow passing through the venous system. Central venous pressure in IIH has been found to be elevated due to obesity in adults.
The Role of Venous Sinus Stenosis
Children referred to a tertiary hospital to rule out IIH may have an increased risk of raised venous sinus pressure. An increase in sinus pressure could be due to obesity, venous outflow stenosis, or cerebral hyperemia.
Compared to controls, patients at risk for IIH had a 17% reduction in transverse sinus and a 14% reduction in sigmoid sinus effective cross-sectional area (p = 0.005 and 0.0009). In children with the chronic headache/IIH spectrum, the highest associations were with cerebral hyperemia and mild venous sinus stenosis.
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Investigating Cerebral Hemodynamics
An MRI with magnetic resonance venography (MRV) and blood flow quantification has been performed over a 10-year period as a comprehensive study into children with suspected IIH.
Compared to controls, the patients at risk for IIH had an arterial inflow increased by 34% (p < 0.0001) with a 9% larger brain volume (p = 0.02), giving an increase in CBF of 22% (p = 0.005). The sagittal and straight sinus venous return were reduced by 11% and 4% respectively (p < 0.0001 and 0.0009) suggesting raised venous sinus pressure.
Obesity and IIH: A Complex Relationship
Obese females have over a 10-fold relative risk for developing IIH, and weight loss almost universally results in reversal of the disease. However, weight loss is also very difficult for most patients to achieve.
In those 42 patients at risk for IIH, the BMIs were larger than the controls at 20.5 ± 7.8 (p = 0.05), with 7 overweight and 10 obese, the average percentile score was 64 ± 14% being larger than the controls (p = 0.03). Obesity was not significantly different in this cohort.
Venous Sinus Stenting: An Emerging Treatment Option
Over the past decade, there has been growing interest in venous sinus stenting as a primary treatment for idiopathic intracranial hypertension (IIH) refractory to medical therapy. The big question now is whether or not venous sinus stenting should be accepted as standard of care in the management of IIH.
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Some groups have advocated the use of venous sinus stenting as a treatment for IIH with headache but no papilledema; however, rates of headache improvement with venous sinus stenting are hit or miss, especially because many patients with IIH also have a history of migraine, which does not respond to stent therapy.
Overall, the literature has shown that IIH stenting is very effective in improving papilledema. Rates of papilledema improvement as determined by ophthalmologists are > 90% in most observational cohort studies. About 90% of patients who present with pulsatile tinnitus from venous sinus stenosis also have improvement or resolution with venous sinus stenting, and headache improvement is reported in about 80% of patients.
Interventionalists should be cognizant that complications are likely underreported. Hemorrhage from venous perforation occurs in approximately 2% of reported cases and often results in subdural or epidural hematoma.
Weight Loss Following Venous Sinus Stenting
This study shows that venous sinus stenting leads to modest weight reduction in IIH patients, and those with resolved papilledema experience slightly greater weight loss.
Patients had a mean pre-operative weight of 103.2 kg, which decreased to 101.5 kg at 3-month follow up (p = 0.0757). Patients at 6-month follow-up saw a weight decrease to 97.4 kg (p = 0.0066). Patients who saw papilledema resolution saw a mean greater decrease in weight (-4.5%) at 6-month follow up than those whose papilledema did not resolve (-1.7%), although this was insignificant (p = 0.1091). A total of 41 patients were included in the meta-analysis.
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Diagnostic Criteria for IIH
To diagnose patients with IIH, the two most widely accepted criteria used are the modified Dandy criteria and the criteria put forth by Friedman et al in 2013.1 At our center, and at many other centers across North America, the Friedman criteria are becoming more accepted because they include a combination of imaging and clinical criteria.
To identify ideal patients for IIH stenting, we are careful to primarily select only those who have papilledema because (1) papilledema is the most debilitating long-term consequence of IIH, and (2) there is a strong correlation between improvement in papilledema and venographic and manometric findings (ie, is the stent actually doing what it is supposed to do).
Devices Used in Venous Sinus Stenting
First, there are currently no “on-label” devices for venous sinus stenting. Our group has historically used a setup that includes a 6-F guiding sheath and advancing a Carotid Wallstent (Boston Scientific Corporation) over 0.014-inch guidewires to cross the lesion. However, the Wallstent is a relatively stiff system and often has some difficulty making sharper turns, particularly in patients with high-riding jugular bulbs or high-grade stenosis. Plus, the Wallstent does not allow for coverage of the entire transverse sinus given its shorter lengths. More recently, we have shifted to using the Zilver 518 stent (Cook Medical), which comes in diameters up to 9 mm, lengths up to 80 mm, and can be used with 6-F catheters such as the Navien (Medtronic). We have found that it is much easier to deliver this stent than the carotid stents we have tried. If approved, it would be the first on-label device for IIH stenting.