Imaging-based selection

In general, most studies report using non-invasive imaging-based selection criteria to determine patient selection to undergo diagnostic catheter angiography. The reasons most commonly cited for obtaining non-invasive imaging prior to the venogram are to exclude other causes of ICP, and evaluation of stenosis prior to performing angiography. The most frequently used non-invasive imaging techniques in patients with IIH for diagnostic angiography are CT venography (CTV), magnetic resonance venography (MRV), or both.10 11 18–32 Multiple studies use demonstrated stenosis on CTV or MRV as criteria for proceeding with diagnostic catheter angiography, and three studies specifically cite requiring stenosis >50% when deciding whether or not to proceed with stenting.18 19 33MRI and CT scans are frequently used to rule out other potential causes of increased ICP such as a mass lesion.20 21 Some studies also use magnetic resonance angiography (MRA) to rule out other potential causes.10 19 22–24 Of the studies reviewed, 23 out of 29 (79%) obtained non-invasive imaging prior to having patients proceed with diagnostic angiography. Of the 23 studies that utilized imaging-based selection criteria, 20 (87%) used CTV, MRV, or both in search of radiographic signs of venous sinus stenosis prior to stenting patients. Six of the 29 studies did not use imaging-based selection criteria for angiography.

Studies have suggested, however, that transverse sinus hypoplasia or stenosis are found at relatively high frequencies in the normal population. Durst et al found the prevalence of unilateral transverse sinus stenosis or hypoplasia in the normal population to be 33% and the prevalence of bilateral transverse sinus stenosis to be 5%.25 Radvany et al observed in a study of 12 patients that two patients who underwent catheter venography had no pressure gradient, despite apparent transverse sinus stenosis on CTV.26 These findings suggest that CTV and MRV may have suboptimal sensitivity or specificity in predicting symptomatic venous outflow obstruction. Ultimately, CTV or MRV may be worthwhile to diagnose an area of anatomical stenosis but are unable to determine whether that is associated with a physiologic gradient. In one study where all medically refractory patients underwent catheter angiography regardless of MRV findings at time of referral, MRV sensitivity was <0.5 in detecting a significant stenosis associated with a pressure gradient.27 In a second retrospective study of venograms with manometry, Levitt et al found that only 65% of patients with prior non-invasive imaging (CTV/MRV) demonstrated dural venous sinus abnormalities on imaging.28

It is reasonable to suggest that providers obtain non-invasive imaging prior to having patients with IIH undergo diagnostic angiography, as imaging findings of stenosis in the setting of IIH are highly associated with pressure gradient findings on diagnostic angiography and manometry. In addition to the presence or absence of stenosis, non-invasive imaging can provide other information that may be useful to know prior to performing a cerebral angiogram. For instance, a dural arteriovenous fistula can present with some of the symptoms of IIH, particularly those with pulse-synchronous tinnitus. It is also useful in identifying a hypoplastic or atretic sinus. If the subsequent catheter angiography includes arterial imaging, this may not be critical information to know ahead of time. However, if the planned catheter angiography is limited to venous imaging and pressure measurements, knowledge of a hypoplastic transverse sinus may influence the subsequent intracranial catheterization and limit the associated risks. While MRV can be useful, it is also reasonable to use catheter angiography with manometry without prior non-invasive venographic imaging based on the conflicting evidence regarding incidence of stenosis in the normal population and lack of gradient with evidence of stenosis. It is possible to find a pressure gradient in the absence of stenosis on non-invasive imaging, and therefore one could argue that a diagnostic venogram should be performed on patients with IIH regardless of MRV or CTV findings.

Medically refractory symptoms

Failed medical treatment for IIH is one of the most consistent indications for a patient with IIH to undergo diagnostic catheter angiography. According to Donnet et al, failed medical treatment is defined as persistent visual symptoms or persistent headaches in spite of treatment with acetazolamide.22 Most of the studies reviewed report performing angiography in patients who have failed medical treatment and thus have persistent visual symptoms or persistent headaches in spite of treatment with acetazolamide.10 18 19 21 22 24 26 29 31 34–36 Of the studies reviewed, 18 out of 29 (62%) mentioned using a medically refractory disease course as an indication for a patient to undergo diagnostic angiography. Of the meta-analyses that were reviewed, none specifically mentioned using medically refractory symptoms as an indication for patients to proceed with angiography. Two studies reported using fulminant vision loss as an indication regardless of whether the patient was medically refractory.29 30

Given that the majority of studies reviewed used medically refractory symptoms as selection criteria, it is likely reasonable to proceed with diagnostic angiography in patients with IIH who meet medically refractory selection criteria.

Intracranial pressure

Elevated ICP, most commonly documented by an elevated opening pressure on lumbar puncture, is a fundamental diagnostic criterion for IIH. There is some speculation that higher levels of opening pressures on lumbar puncture may correlate with a higher likelihood of finding venous sinus stenosis on angiography. However, there is little published literature that investigates this correlation. Ahmed et al found that patients with higher opening pressures were more likely to require additional stenting than those with lower opening pressures. For example, of the 52 patients in the study’s cohort, all of which received one stent initially, six ended up needing an additional stent placed. The six patients that required additional stenting had a mean opening pressure of 35 cm H₂O compared with a mean opening pressure of 31 cm H₂O in the group that did not require additional stenting.31 A similar study by Goodwin et al also showed that patients with a higher opening pressure were associated with needing a shunt placement post venous sinus stenting.32 In addition, Kumpe et al showed that patients with higher mean opening pressures were also more likely to have hemodynamic failure and require retreatment.37 It remains uncertain what specific angiographic findings or stenting outcomes can be elucidated from higher mean opening pressures. Future studies should aim to investigate further the role of mean opening pressures as an isolated variable and its role in venographic findings and stenting outcomes.

Many of the studies involved in the literature review included patients with elevated intracranial pressures on lumbar puncture. However, the intracranial pressure threshold that each study used was not generally mentioned. According to the accepted modified Dandy criteria, a patient must have a CSF opening pressure of at least 25 cm H₂O to meet the diagnosis of IIH, thus suggesting that most studies performed venography on patients with CSF opening pressures greater than 25 cm H₂O. In addition, Levitt et al found that 35% of patients with IIH undergoing venous manometry had a venous sinus pressure gradient of ≥8 mm Hg and that 0% of patients with normal ICP had a venous sinus pressure gradient of ≥8 mm Hg, suggesting that a normal ICP indicates a very low likelihood of detecting a significant pressure gradient.28

Body mass index

IIH is often found in overweight and obese women, with many studies reporting body mass index (BMI) in patients undergoing venous sinus stenting.14 Raper et al found that higher BMI was associated with higher pressure gradients as well as greater improvement in pressure gradient after treatment.38 However, there are no studies reporting whether BMI is correlated with the likelihood of venous sinus stenosis.

Manometry

Venous manometry is frequently used in detecting a pressure gradient in the venous sinuses in patients with IIH. All available studies, 29 out of 29 (100%), support the use of venous manometry to detect a pressure gradient across the region of sinus stenosis prior to stenting to assess candidacy for treatment. Of the 29 studies, the average pressure gradient found in study patients ranged from 12.4 to 30.0. Given its ability to accurately detect physiologically-relevant venous outflow obstruction, manometry is an invaluable technique in assessing whether or not a patient is a candidate for treatment prior to undergoing venous sinus stenting.

While there are no data supporting a threshold in the literature, most studies report using a pressure gradient >8 mm Hg for consideration of venous sinus stenting.29 31 34 35 39 40 The original 8 mm Hg gradient reported by Ahmed et al was arbitrarily selected as a reasonable threshold and was not generated based on scientific or empiric testing or observations.31 Other studies have reported using gradients as low as >4 mm Hg26 30 32 36 or as high as >10 mm Hg.33 37 41 42 A recent systematic review showed that higher pressure gradients are associated with higher rates of clinical success, with 94% of patients with a pressure gradient of 22 mm Hg or more having favorable outcomes compared with 82% of patients with gradients of 21 mm Hg or less.15

In theory, complete correction of a 7 mm Hg gradient with stenting would result in an approximate decrease in ICP of 9–10 cm H₂O. Therefore, it seems reasonable to use a pressure gradient threshold of 6–8 mmH g when assessing candidacy for stenting.

Arteriography

Diagnostic catheter angiography often includes selective catheterization and angiography of bilateral internal and external carotid (or common carotid) and vertebral arteries to evaluate cerebral venous anatomy, venous outflow patterns, and to rule out arteriovenous shunting or fistulae. While all authors have supported venography and venous manometry as the primary method for establishing candidacy for stenting, there are no published data to suggest that arteriography is necessary in assessing candidacy for stenting. Given the practical diagnostic capabilities of arteriography as well as its high sensitivity in ruling out arteriovenous fistulae as a confounder, performing concomitant selective arteriography is reasonable and probably should be performed as part of the diagnostic process for patients with IIH. This may be particularly important in patients who have not had preoperative non-invasive venous or arterial imaging.

Anesthesia choice during angiography

Anesthesia during angiography is a topic of current debate. In addition, there is currently no consensus among reports on the type of anesthetic used during venography. Of the 29 studies reviewed, seven (24%) were found to use general anesthesia when performing venography. Several authors have reported performing concomitant diagnostic venography and stenting under general anesthesia as a single procedure.23 42–44 Patients were awake during venography in 14 out of the 29 studies reviewed (48%).

Recently, two retrospective series have shown that there are significant differences in venous sinus pressure measurements when under general anesthesia compared with when awake. These studies both discovered that general anesthesia tends to underestimate pressure gradients across regions of stenosis compared with values obtained while awake.45 46 Based on these factors, authors have recommended that diagnostic venography be performed with the patient awake or under conscious sedation as opposed to general anesthesia.

Microcatheter for manometric evaluation

The choice of microcatheter for manometric recording is often not reported in the literature. Some studies report using a 0.027 inch Renegade Hi-Flo microcatheter.10 31 40 41 A study comparing the accuracy and precision of microcatheters found that the Echelon 10, Prowler Select Plus, and Marksman 27 met ICP device monitoring standards while Excelsior SL-10 did not meet the standards and Excelsior 1018 met the standards variably.47

Stent

There is no recommendation for the type of stent device implanted, as a variety are reported in the literature. These include Zilver,18 19 33 35 37 38 40 41 Precise,8 10 19 24 33–35 38 Wallstent,30 38 44 Protégé,10 24 38 43 and SMART,41 44 48 among others. There are no studies in the literature comparing the type of stent used with clinical outcomes and complication rates, therefore there is no evidence to support the use of a certain stent. An ongoing study, OPEN-UP (NCT number NCT01003639), which is looking at venous sinus stenting versus ventriculoperitoneal (VP) shunt placement, uses the Zilver stent.

Unilateral versus bilateral stenting

There are no studies reporting specifically on synchronous bilateral transverse sinus stenting for patients with IIH. The vast majority of published series performed unilateral stenting with good procedural outcomes.

Number of stents

The number of stents used per patient appears to be variable and is not often reported in the literature. Some report using a single stent per patient19 31 48 while others report numbers as high as an average of 1.4 stents per patient.11 38 Of interest is whether higher numbers of initial stents placed is associated with better outcomes. However, review of the literature found no studies investigating whether the initial number of stents is associated with a lower need for retreatment or with failure of treatment.

Antiplatelet agents

In general, most studies report using dual antiplatelet therapy of aspirin and clopidogrel for varying durations.10 18 26 29 33 35 36 39 40 Many studies report using heparin during the procedure.19 22 30 31 41 42 44 Teleb et al reported that the most common antiplatelet regimen was aspirin and clopidogrel 3–5 days pretreatment, heparin during treatment, and aspirin and clopidogrel for 3–6 months post treatment, followed by aspirin for a year or more. Teleb et al reported that, of the 207 patients treated, there were two reports of in-stent thrombosis.13 The two reports of in-stent thrombosis occurred in the same study where aspirin alone was used as antiplatelet therapy.21 No studies using dual antiplatelets reported intraluminal thrombotic complications. Two other studies reported using single agent antiplatelet therapy with aspirin or clopidogrel alone, encompassing a total of 20 patients, with no reported complications.11 22 There is not sufficient evidence in the literature to suggest the inferiority of using a single antiplatelet regimen.

Post-stent manometry

Post-stenting manometry was performed immediately after stenting in 26 of the 29 (90%) reviewed studies in order to confirm resolution of a pre-procedural pressure gradient. The three studies that did not specifically mention performing post-stenting manometry document performing post-stenting angiography in order to confirm patency of a post-procedural stent.18 19 33 There has yet to be an independent assessment of the necessity of post-stent manometry in confirming treatment success. In the absence of such a study, the literature strongly supports using post-stent manometry based on its use in the overwhelming majority of studies.

Recommendations

• There are limited data on the criteria for retreatment or for the optimal retreatment strategy. It is reasonable to repeat angiography and manometry on patients with recurrence of symptoms after resolution with stenting to evaluate for recurrent stenosis (Strong).