Article Text
Abstract
Background Flow-diverter stent (FDS) placement for treatment of intracranial aneurysms can cause flow changes in the covered branches.
Objective To assess the impact of the treatment of carotid siphon aneurysms with FDS on the posterior communicating artery (PComA) flow.
Materials and methods Between February 2011 and January 2015, 125 carotid siphon aneurysms were treated with FDS. We retrospectively analyzed all cases with PComA ostial coverage. The circle of Willis anatomy was also studied as the flow changes in PComA postoperatively and during angiographic follow-up. Data from neurological examination were also collected.
Results Eighteen aneurysms of the carotid siphon in 17 patients were treated with FDS covering the ostium of the PComA. Based on the initial angiography, patients were divided into two groups: the first with a P1/PComA size ratio >1 (10 cases) and the second with a ratio ≤1 (8 cases). Follow-up angiography (mean time of 10 months) showed 90% of PComA flow changes in group 1 but only 12.5% in group 2. There was a significant difference between the two groups (p=0.002). Nevertheless, no patient had new symptoms related to these flow changes during the follow-up period.
Conclusions In our experience, covering the PComA by FDS when treating carotid siphon aneurysms appeared safe and the P1/PComA ratio is a good predictor of flow changes in PComA.
- Aneurysm
- Stent
- Flow Diverter
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Introduction
Wide neck aneurysms can be a challenge for endovascular treatment. Flow-diverter stents (FDS) have proved to be efficient for the treatment of large and broad-necked carotid siphon aneurysms.1 The mechanism by which they induce aneurysm occlusion is by redirecting flow away from the aneurysm sac to the parent vessel. Once placed, struts of the stent support neointimal growth, which contributes towards remodeling the artery as well as permanently occluding the aneurysm.2
A recurrent concern about the use of FDS relates to their occlusion of side branches. When placed within the internal carotid artery, the main problem is the coverage of the ophthalmic artery (OphA), the posterior communicating artery (PComA), and the anterior choroidal artery (AChA).
Some studies have evaluated carotid siphon branch occlusion. However, the majority evaluated the Pipeline embolization device (PED) and were concerned about OphA or AChA occlusion.3–7
In this study, we reviewed patients who underwent endovascular treatment for carotid siphon aneurysms and selected those in whom the PComA ostium had been covered by one of the main FDS available in France: PED (Covidien, Irvine, California, USA), Silk stent (Balt, Montmorency, France), Surpass stent (Stryker Neurovascular, Fremont, California, USA), or FRED stent (MicroVention, Tustin, California, USA). The aim of our study was to evaluate the incidence of PComA occlusion and correlate this to its size compared with the ipsilateral P1 segment.
Methods
Population
Between February 2011 and January 2015, 110 consecutive patients with 125 carotid siphon aneurysms treated with FDS were retrospectively reviewed to assess the incidence of PComA ostium coverage using conventional digital subtraction angiography (DSA) and multiplanar reconstruction (VasoCT).8 ,9
All endovascular treatment was performed using a biplane, flat-panel detector angiography system (Allura Xper 20/10; Philips Healthcare). Conventional 2D DSA and VasoCT were routinely performed on the day of the procedure to confirm a good wall apposition (figure 2), and in the follow-up angiograms at 6, 18, and 42 months after treatment to check for any in-stent stenosis. Non-routine additional angiograms were obtained at the discretion of the physician and when unexpected clinical or angiographic findings were seen during follow-up. Informed consent was obtained from each patient. The inclusion criteria in this study were (1) PComA ostium covered by a FDS and (2) at least one follow-up angiogram at 3 months or later.
Treatment technique
Endovascular procedures were performed with the patient under general anesthesia and systemic heparinization. Patients were premedicated with clopidrogrel (75 mg daily) and aspirin (160 mg daily) starting 7 days before the procedure. Thrombocyte inhibition levels were confirmed using the VerifyNow P12Y12 assay (Accumetrics, San Diego, California, USA) and four hematological laboratory tests.
Other than a few exceptional cases in which the protocol was changed at the physician's discretion, the dual antiplatelet therapy was maintained for 3 months then discontinued, while aspirin was continued until 12 months after treatment.
All endovascular procedures were performed in a triaxial fashion and the materials used depended on the operator's choice.
Statistical analysis
For comparison, the patients were divided into two groups according to the relationship between the size of the PComA and the ipsilateral P1 segment: group 1 had a larger P1 than PComA (P1/PComA ratio >1) and group 2 either had a P1 that was smaller than or the same size as PComA or had a fetal type anatomy (P1/PComA ratio ≤1).
For statistical analyses, XLSTAT software (V.2015.5.01.23755) was used and differences between the two groups were assessed by Mann–Whitney test. Values of p<0.05 were considered statistically significant.
Results
The data for PComA size compared with the ipsilateral P1 segment (P1/PComA ratio), and its status immediately after treatment and during follow-up are summarized in table 1. The aneurysm location and its previous (ruptured vs non-ruptured) and follow-up status (occluded, partially occluded, or non-occluded), as well as type and number of FDS and duration of follow-up are also shown.
A total of 17 patients (3 men and 14 women) with 18 aneurysms met the inclusion criteria and were analyzed in this study. A total of 22 stents were used (14 Silk, 2 Surpass, 4 FRED, and 2 Pipeline). The average number of FDS used for each aneurysm was 1.2. The medium aneurysm diameter was 8.7 mm (range 3–21 mm). The mean age was 50 years (range 23–70 years). One patient treated with FDS for a carotid siphon aneurysm on both sides was included and each side was independently analyzed. The duration of follow-up ranged from 3 to 25 months, with a mean time of 10 months (median 7.5 months). Three cases were ruptured aneurysms previously treated with coils. Four patients were treated with two FDS but in one of these cases only one FDS covered the PComA ostium. The overall rate of aneurysm complete occlusion, partial occlusion, and non-occlusion at follow-up were 72%, 11%, and 17%, respectively. The rate of complete occlusion according to each group was 90% in P1/PComA >1 and 50% in P1/PComA ≤1. The duration of follow-up was similar in both groups—10.4 and 10.6 months, respectively.
PComA was occluded in three patients (17%) immediately after the FDS placement, and was confirmed on the follow-up. Three more patients (17%) showed a reduced flow rate in PComA after treatment, one of whom (5.5%) had a completely occluded PComA on follow-up and the other two (11%) showed a persistently reduced flow rate on the last control angiogram. One patient (5.5%) in whom no modification of flow was found immediately after FDS placement showed occlusion at the follow-up at 7 months. All seven (39%) of these patients presented a smaller PComA than P1 segment in the initial angiography.
Patient number 7 showed a reduction in flow rate and size of PComA at follow-up associated with a slight increase in the size of the ipsilateral P1. This was the only case in our series in which PComA was larger than P1 at baseline and showed a flow change on PComA after FDS placement.
Only one patient had a fetal PComA covered by one FDS and no hemodynamic change was noted during treatment or at 7 months’ follow-up (figure 1).
In our study, no patient experienced symptoms related to PComA occlusion. One patient had visual symptoms 1 day after the intervention. IV thrombolytic abciximab was given, which allowed partial clinical improvement. MRI showed no changes in the posterior cerebral artery (PCA) territory and the symptoms were attributed to ophthalmic artery thrombosis.
Summarizing the data collected, we found 10 cases (56%) with PComA flow changes (occluded, reduced flow rate or diminished in size) on follow-up related to the FDS placement. Among these 10 cases, nine (90%) had a P1/PComA size ratio >1. On the other hand, only one (12.5%) out of the eight with a P1/PComA size ratio ≤1 had flow changes on follow-up. There was a significant difference between the two groups with a p value equal to 0.002 (table 2).
Discussion
Patients in our series displayed a similar incidence of PComA flow changes after FDS placement to those reported in the literature.3 ,7 ,10 ,11 In our study, 28% of PComA were occluded on follow-up and a total of 56% showed flow changes related to flow diversion. According to our data, two different groups of patients can be categorized, with different levels of risk exposure to PComA flow changes: (1) PComA smaller than P1 (P1/PComA ratio >1), with a high risk of hemodynamic changes in PComA (ie, artery occlusion, reduced flow rate, or reduction in size); and (2) PComA equal in size to or larger than P1 or fetal type (P1/PComA ratio ≤1), with a low risk of flow changes. In our series, FDS covering the PComA ostium appeared to be safe and no patient had new neurologic symptoms related to flow changes.
The role of FDS in the treatment of aneurysms located in the carotid siphon is well established and the effects on the main collateral branches are a recurrent concern. Although flow changes on side branches due to FDS are relatively common, investigation shows that related clinical symptoms are rare. Thus, owing to their mostly clinically silent presentation, the real incidence of flow changes over side branches of the carotid siphon is difficult to estimate and could range from as low as 1.4% to as high as 45%.7 ,11 ,12
Neki et al5 reported no flow changes or related clinical symptoms after AChA ostium occlusion by FDS insertion. In their study on AChA patency in 15 patients, Brinjikji et al6 found just one occlusion but no related neurologic symptoms or strokes.
Yet Puffer et al4 studying ophthalmic artery status after flow diversion found a 21% incidence of thrombosis at follow-up. The mean number of PED implanted into the patients with occluded OphA at follow-up was 2.4 compared with the 1.9 in the patients with no change in OphA flow. During the period in which this work was published, it was common practice to deploy more than one device in a telescopic fashion and one may argue that this might have had some influence. In a recently published study including 28 cases of carotid siphon aneurysms treated with FDS across the OphA ostium, Rouchaud et al13 showed that although 85.7% had a patent OphA after endovascular treatment, 39.3% of patients presented a new ophthalmic deficit in an extensive ophthalmic evaluation performed 1 week after treatment.
Limited data concerning PComA status after FDS have been published. In their study on intracranial aneurysms treated with PED, Yu et al11 showed a 1% rate of side branch occlusion (two cases, both PComA), although the incidence of PComA ostium covering was not mentioned. In their series, Vedantam et al3 found just one PComA occlusion among the 14 cases in which its ostium was covered by a PED and the patient showed no new neurologic deficit. Brinjikji et al,7 however, found 27% of complete occlusion and 18% of diminished flow on follow-up when PComA was covered by FDS. To our knowledge only one study concerning PComA ostium covering by FDS in patients with fetal PCA anatomy has been published, by Kan et al.10 In their experience based on four cases, no patient presented flow changes in the PComA after FDS implantation. On the other hand, all four aneurysms remained patent on follow-up, leading the authors to suggest that FDS is not an efficient technique for the treatment of fetal PComA aneurysms. Corroborating these data, our only patient with fetal PCA anatomy presented no change in PComA flow and the aneurysm remained unchanged at the 7-month follow-up. We also had a low aneurysm occlusion rate in the group with P1/PComA ≤1 (50%), suggesting that the elevated flow in PComA in this type of anatomy may inhibit or postpone aneurysm occlusion. A longer follow-up is required to confirm this theory.
The theory of gradient pressure may explain why small perforators usually remain patent after flow diversion whereas collateral vessels, even when large like PComA or OphA, may tend towards thrombosis. The sump pressure in terminal vessels appears therefore responsible for their persistent patency, while collateral flow is more implicated in occlusion.14–16 Animal studies indicate that the perfusion demand of tissue supplied by FDS-covered branches is responsible for their permeability.17 In the most common pattern of posterior circulation in which a P1 segment is present, the direct anastomotic connection to PComA is a source of flow competition and explains the high incidence of flow disturbances in PComA after FDS placement. On the other hand, a fetal PCA is an end vessel with no direct collaterals and its demand tends to create a sufficient pressure gradient across the ostium to maintain flow within the PComA and aneurysm patency, even after placement of a flow diverter.10
The patency of the anterior thalamoperforating branches, arising mainly from the anterior part of PComA,18 could not be assured angiographically. However, we noted no perforating stroke in our series, suggesting that these branches, together with the PComA, might still be patent even if this PComA was not opacified further during the angiography. We referred to the PComA as being ‘occluded’ when it was no longer visible at follow-up, although we did not perform a balloon occlusion test to prove it.
Our study is limited by its retrospective design and also by the small number of patients. In our series just 14% of cases (18/125) of carotid siphon FDS met the inclusion criteria. Indeed, in most cases and particularly those during the first years of our FDS experience, we made every effort to avoid covering the PComA ostium owing to a lack of relevant scientific data concerning FDS placement covering side branches. Moreover, our follow-up was short and a long-term follow-up is required to better evaluate the effect on flow change of FDS for the treatment of carotid siphon aneurysms.
Conclusion
In our experience, covering the PComA by FDS in the treatment of carotid siphon aneurysms appears safe, even in patients with fetal-type anatomy. The size ratio P1/PComA appears to be an accurate tool to predict flow changes in the PComA after FDS implantation and should be considered in planning treatment of carotid siphon aneurysms.⇓⇓⇓
References
Footnotes
Contributors FMdC: contributed to the conception and design of the study, collected and interpreted the data, drafted the article and coordinated the group, critically revised the article and approved the final version. JC: contributed to the conception and design of the study, interpreted the data and performed the statistical analysis, drafted the article and coordinated the group, critically revised the article and approved the final version. EPdSN: acquired and analyzed the data, critically revised the article and approved the final version. VC, HAK, AR, GS, HN: acquired the data, critically revised the article and approved the final version. JM, LS: participated in conception of the study, interpreted the data, critically revised the article and approved the final version.
Competing interests JM, LS: consultants for Covidien, MicroVention, and Stryker.
Ethics approval Beaujon ethics committee.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The authors are willing to share spreadsheets from their data extraction on request.