Veins and Drains: Stenting Venous Sinus Stenosis can Reverse IIH and Treating IIH can Reverse Venous Sinus Stenosis

Two articles in this issue of the Journal of Neuro-Ophthalmology from the group at the University of Toronto shed new light on the now well-established practice of treating medically refractory patients with idiopathic intracranial hypertension (IIH) with venous sinus stenting. In their article, “Visual and Pharmacotherapy Outcomes After Transverse Sinus Stenting for IIH,” Handzic et al1 add to the growing body of evidence that venous sinus stenting can help improve neuro-ophthalmic outcomes, even as medical therapy with acetazolamide or topiramate is tapered or stopped. Specifically, they found that in 15 patients, 9 of whom failed medical therapy, 2 of whom could not tolerate it, and 4 of whom had “fulminant” presentations, 71% were able to stop medications that lower intracranial pressure (ICP), while 29% were able to taper them over a median of 66.9 weeks of follow-up. Regarding patient symptoms, there was resolution of headache in 77%, pulsatile tinnitus in 80%, diplopia in 67%, and transient visual obscurations in 50%. Although Frisén grading was not provided, papilledema resolved in 22/30 eyes and improved to “mild” in the remaining 8. Furthermore, assessment of the peripapillary retinal nerve fiber layer (RNFL) with optical coherence tomography demonstrated that in the 24 eyes with prestent RNFL thickening, there was a significant reduction to either normal or subnormal range in all but 3 eyes, with a median decrease of 147 μm. Improvement in visual acuity (VA) was not statistically significant, but on visual field testing, perimetric mean deviation (PMD) improved by a median of 3 dB. Although this was a substantial change, it is notable that PMD only improved in 48% of the eyes. Importantly, in 4 patients with fulminant IIH (defined as having an initial best-corrected VA worse than 20/40 or an initial PMD worse than 25 dB), VA improved in 3 eyes and stabilized in 3. There was one major complication, thrombosis of the vein of Labbe (VOL), which can occur due to stent wall blockage and secondary stasis within the vein. In this case, it was treated successfully with anticoagulation, but prior cases in the literature of life-threatening acute elevation in ICP after stenting may result from similar VOL occlusions. As the authors pointed out, one limitation of this study was that patients were not asked to complete symptom forms, so if a symptom was not documented in the chart, it was assumed that it was not present. Furthermore, while initial body mass index (BMI) was noted, final BMIs were not, so we do not know how much weight loss may have contributed to patients' ability to stop or reduce ICP-lowering medications, nor how the rates of medication reduction differ from patients treated with medication alone. Finally, we would caution that the authors definition of fulminant IIH (PMD worse than −5dB) meriting immediate stenting without a trial of medications seems a bit liberal since patients with that degree of visual field loss will often improve significantly with medical therapy. Despite these limitations, this well-designed study is a reminder that venous stenting appears to be an effective and relatively safe alternative to other surgical interventions and should be further explored in prospective head-to-head trials. In another study, Handzic et al2 revisit the age-old debate of whether transverse sinus stenosis (TVSS) associated with IIH is reversible with normalization of ICP. From a cohort of 435 patients with papilledema and TVSS, they found 10 in whom papilledema resolved and repeat neuroimaging after resolution was available. Treatment included acetazolamide, topiramate, cerebrospinal fluid (CSF) diversion, or weight loss, sometimes in combination, and follow-up imaging occurred at an average of 11.8 months after presentation. Assessing the severity of TVSS using the Farb 2003 combined conduit score (where 0 signifies the absence of flow in a segment and 4 signifies no stenosis), they found improvement in the degree of TVSS in 50%, only one of which had received CSF diversion, and no change in the remaining patients. The authors conclude that TVSS can reverse even after conservative treatment of IIH and remind us that some forms of TVSS appear to be a downstream effect of IIH. These findings are significant because there can be a misconception that the presence of venous sinus stenosis, without considering the clinical findings or the response to medical therapy, is an absolute indication for stenting. The improvement of TVSS after nonsurgical management of IIH strengthens the argument that the finding of TVSS alone should never serve as a reason to stent patients with IIH. Indeed, it has long been recognized that there are 2 forms of stenosis associated with IIH: The first is an intrinsic form, which is related to swollen arachnoid granulations, septal bands, chronic thrombus, or congenital anatomical variant, and does not reverse even when ICP is lowered. Such fixed stenoses appear to predispose to IIH (although not always), and in the setting of medically refractory IIH, the rationale for stenting is easy to understand. The second type, extrinsic, in which there is gradual narrowing of the vein instead of the focal appearance of intrinsic forms, will reverse with the normalization of ICP. For years, we have seen this form reverse with conservative medical treatment, and we are glad that Handzic et al have demonstrated this in their series. However, many groups3,4 have shown resolution of papilledema and other symptoms and signs of IIH even when such extrinsic stenoses are stented, suggesting that while they may result from IIH, they also contribute to it through a positive feedback loop. This has been modeled mathematically as a Starling resistor5,6 with the notion that eventually, the vein can no longer collapse any further, and the CSF and venous pressure both settle at elevated levels. Since the authors excluded patients with intrinsic stenosis, the lack of reversibility in half of their patients could be explained by several reasons. First, the threshold for lowing of ICP necessary to reverse papilledema might be less than that needed to reverse the stenosis in these patients. Second, although intrinsic stenosis due to significant arachnoid granulations served as an exclusion criterion, it is possible that some of the patients in this study still had intrinsic stenosis related to more subtle granulations or had stenosis with mixed features of both intrinsic and extrinsic elements. It is also conceivable that an intrinsic stenosis can cause elevated ICP, which can then lead to extrinsic stenosis. Finally, as the authors point out, chronic IIH might sometimes lead to dural wall incompetency, precluding a return to the initial caliber as proposed by Lazzaro et al.7 A limitation of this study was the fact that lumbar puncture was not performed even at diagnosis in the majority of patients, so this is not a pure population of IIH. As the authors point out, all the radiological signs typically associated with IIH, including TVSS, can be found in the setting of alternative causes of intracranial hypertension, and we have seen several cases where a premature radiological impression of IIH based on such findings led to a delay in diagnosis of entities such as leptomeningeal disease or viral meningitis. However, there is no reason to suspect that their findings would not apply to patients with either idiopathic or secondary intracranial hypertension. Together, these contributions of Handzic et al to the literature have enhanced our understanding of the nature of the venous contribution to IIH. We support the authors' conclusion that the presence of TVSS should only be one criterion for treatment with neurointervention, along with the overall clinical picture.

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