Q: When do we consider venous sinus stenting (VSS) for patients with idiopathic intracranial hypertension (IIH)?
Most patients (75%) with IIH respond to medical treatment. In refractory patients, there are 3 available options including CSF diversion (ventriculoperitoneal shunt (VPS) or lumboperitoneal shunt (LPS), optic nerve sheath fenestration (ONSF) and VSS. As of now, we do not know which option is the best. There is currently an ongoing randomized controlled trial comparing the efficacy between VPS and VSS (OPEN-Up trial). SIGHT or Surgical Idiopathic Intracranial Hypertension Treatment Trial, which was designed to compare VPS vs ONSF vs medical Rx, was terminated early due to poor recruitment.
VSS was first performed in 2002 by Dr. Higgin and his team which showed significant improvement of trans-stenotic pressure gradient in transverse sinus and patient symptoms after VSS. In the past few years, VSS has become increasingly more popular and current evidence (nonrandomized studies) demonstrates good efficacy and safety of the procedure. VSS is also less invasive compared to other options.
Approximately 30-93% of patients with IIH have either bilateral transverse sinus (TS) stenosis or unilateral TS stenosis with contralateral TS hypoplasia, compares with 6.8% in general population has it. Whether venous sinus stenosis is the cause or the consequence of IIH remains unknown. Evidence to support that venous stenosis is the consequence of IIH in the reversal of stenosis and decrease in tran-stenotic gradient pressure following large volume lumbar puncture or CSF diversion. However, there is conflicting evidence that venous stenosis persists despite normalization of intracranial pressure (ICP).
B) Two types of TS stenosis
There are 2 types of TS stenosis; extrinsic and intrinsic. Patients can have both. Extrinsic stenosis is secondary from external compression of TS from high ICP. Usually, it is a long smoothing narrowing segment of TS. Intrinsic stenosis has acutely marginated filling defect within the lumen. The causes of intrinsic stenosis are arachnid granulation hypertrophy, steal band, chronic venous thrombosis or vasculitis or trabecular etc. Patients with intrinsic stenosis require a second hit (weight gain or altered CSF dynamic) to result in increased ICP. Most patients have extrinsic stenosis type.
C) How to identify TS stenosis and VSS candidate?
MRV is the noninvasive study of choice. One study showed that MRV with gadolinium had less artifacts compared to time of flight (TOF) MRV. We can identify TS stenosis by brain MRI with gadolinium (especially coronal T1 post gadolinium) as well. Once TS stenosis is identified, patient with refractory to medical treatment will need cerebral venous manometry to check trans-stenotic pressure gradient. At this time, the cut off pressure gradient for VSS varies between 4-10 mm Hg, most set at ≥ 8 mm Hg. Venous manometry should be performed under awake setting instead of under general anesthesia (GA) because GA can underestimate the pressure gradient.
D) VSS consideration
The criteria for VSS are not yet well defined. The OPEN-UP trial inclusion criteria for VSS are
1. Age ≥ 18 years old.
2. Diagnosis of IIHT according to the Modified Dandy Criteria. (see figure)
3. Moderate to severe visual field loss defined by perimetric mean deviation of at least -8 dB but better than -30 dB in the worse eye.
4. Diagnostic cerebral venography demonstrating a pressure gradient of ≥ 8 mmHg across at least one segment of the dural venous sinus as measured during transfemoral cerebral venography
5. Failure of conservative or non-surgical therapies (including medications, lifestyle modifications, etc.). Failure is defined by:
▪ absence of visual function improvement after 1 month of treatment (medication treatment failure with acetazolamide (Diamox) is defined as lack of improvement on a dose of at least 3,000mg per day); AND/OR
▪ medication intolerance OR
▪ after two weeks in patients presenting with severe vision loss (perimetric mean deviation (PMD) worse than -12 dB in the worse eye) OR
▪ per investigator discretion given sufficient worsening of vision loss
E) What is the current evidence of VSS for patients with refractory IIH?
Kalyvas et al published the largest systemic review of surgical treatments of IIH with results summarized in Table (see figure below). They found 825 patients who had VSS in their review, and they reported that VSS improved papilledema, visual fields and headaches in 87.1%, 72.7% and 72.1% of the patients, respectively with 9.4% complication rate (2.3% severe complication) and 11.3% failure rate. VSS normalized CSF pressure in 92.8% of cases. Furthermore, VSS provided the best results in headache resolution visual outcomes with low failure rate and very favorable complications. They suggested that VSS ought to be regarded as the first-line surgical modality of treatment for refractory IIH.
Whether or not the stent works fast enough to normalize CSF pressure to prevent optic nerve damage, the current evidence shows only 8% of those with papilledema at onset were left with optic atrophy. The treatment failure of VSS due to sinus restenosis is 12.3%. Gurney et al mentioned in their review that “the potential predictors for re-treatment have shown possible evidence that raised BMI and that the African-American race is associated with higher retreatment rates. Haemodynamic failure was strongly associated with the female gender and pure extrinsic compression of the transverse-sigmoid junction. Patients with highly raised opening pressures and those with persisting papilloedema post-procedure are at increased risk of stent failure.”
F) What are the potential complications of VSS procedure?
The most common complication is transient headache due to dural stretching from the stent (50%). The risk of cortical vein perforation which leads to severe intracranial hemorrhage and death are risks unique to VSS. (see figure)
Kalyvas A, Neromyliotis E, Koutsarnakis C, Komaitis S, Drosos E, Skandalakis GP, Pantazi M, Gobin YP, Stranjalis G, Patsalides A. A systematic review of surgical treatments of idiopathic intracranial hypertension (IIH). Neurosurg Rev. 2020 Apr 25.
Gurney SP, Ramalingam S, Thomas A, Sinclair AJ, Mollan SP. Exploring The Current Management Idiopathic Intracranial Hypertension, And Understanding The Role Of Dural Venous Sinus Stenting. Eye Brain. 2020 Jan 14;12:1-13.
Farb RI, Vanek I, Scott JN, Mikulis DJ, Willinsky RA, Tomlinson G, terBrugge KG. Idiopathic intracranial hypertension: the prevalence and morphology of sinovenous stenosis. Neurology. 2003 May 13;60(9):1418-24.
Morris PP, Black DF, Port J, Campeau N. Transverse Sinus Stenosis Is the Most Sensitive MR Imaging Correlate of Idiopathic Intracranial Hypertension. AJNR Am J Neuroradiol. 2017 Mar;38(3):471-477.
Dinkin MJ, Patsalides A. Venous Sinus Stenting for Idiopathic Intracranial Hypertension: Where Are We Now? Neurol Clin. 2017 Feb;35(1):59-81.