Original Article
A computational fluid dynamics (CFD) study of WEB-treated aneurysms: Can CFD predict WEB “compression” during follow-up?

https://doi.org/10.1016/j.neurad.2017.03.005Get rights and content

Abstract

Background

Recent reports have revealed a worsening of aneurysm occlusion between WEB treatment baseline and angiographic follow-up due to “compression” of the device.

Objective

We utilized computational fluid dynamics (CFD) in order to determine whether the underlying mechanism of this worsening is flow related.

Methods

We included data from all consecutive patients treated in our institution with a WEB for unruptured aneurysms located either at the middle cerebral artery or basilar tip. The CFD study was performed using pre-operative 3D rotational angiography. From digital subtraction follow-up angiographies patients were dichotomized into two groups: one with WEB “compression” and one without. We performed statistical analyses to determine a potential correlation between WEB compression and CFD inflow ratio.

Results

Between July 2012 and June 2015, a total of 22 unruptured middle cerebral artery or basilar tip aneurysms were treated with a WEB device in our department. Three patients were excluded from the analysis and the mean follow-up period was 17 months. Eleven WEBs presented “compression” during follow-up. Interestingly, device “compression” was statistically correlated to the CFD inflow ratio (P = 0.018), although not to aneurysm volume, aspect ratio or neck size.

Conclusion

The mechanisms underlying the worsening of aneurysm occlusion in WEB-treated patients due to device compression are most likely complex as well as multifactorial. However, it is apparent from our pilot study that a high arterial inflow is, at least, partially involved. Further theoretical and animal research studies are needed to increase our understanding of this phenomenon.

Introduction

The WEB intra-saccular flow disrupter (Sequent Medical, Alisa Viejo, California) is a novel endovascular approach to treat broad base intracranial aneurysms. A recent report has demonstrated a worsening of aneurysm occlusion between postoperative baseline and follow-up due to “compression” of the device [1]. Cognard et al. described a worsening between the post-procedural and follow-up angiographies in 10 of 14 cases (71.5%) and a “compression” of the WEB in 9 of 14 cases (64.3%) (Fig. 1). In a larger series, other authors [2] demonstrated that this phenomenon was not infrequent with a WEB shape modification in 32% of cases.

Yet the underlying mechanisms are still unknown. The WEB device is expected to better resist arterial flow due to its volumetric shape and radial force, therefore some suspect that WEB shape is modified by clot retraction [3].

However, neither mechanism has yet been demonstrated. Here, we sought to determine whether the reported worsening of aneurysm occlusion is flow related using computational fluid dynamics (CFD) technology.

Section snippets

Data collection

From our prospectively maintained database, we retrospectively extracted all consecutive patients treated with a WEB device in our institution between July 2012 and June 2015 for either a middle cerebral artery (MCA) or basilar tip aneurysm, that were unruptured, untreated and without partial thrombosis. Informed consent was obtained in each case. The study was conducted under the rules of local ethics committee. Patients with obvious bad technical results were excluded, i.e. absence of neck

Demographic data

Between July 2012 and June 2015, a total of 22 unruptured MCA and basilar tip aneurysms, that had never received treatment, were operated on with a WEB device in our institution (Table 1). A total of 18 patients (15 women and 3 men; average age 64 years), with 19 WEB-treated aneurysms were included in this study. Three cases were excluded for different reasons:

  • one patient had obvious post-detachment negative results (with flow around the device) and is planned to be retreated in a second

WEB “compression”

The WEB intra-saccular flow disrupter was first introduced to the market as an exciting device since it appeared to be a simple solution for managing previously difficult-to-treat wide-neck bifurcation aneurysms, in addition to a very good safety profile [8], [9], [10], [11], [12], [13], [14]. However, it has recently been described in an unexpected phenomenon: during early follow-up, a worsening of the occlusion rates, related to “compression” of the device, had been observed in up to 64% of

Conclusion

The mechanisms underlying in WEB shape change with time, as observed in some aneurysms, are most likely complex as well as multifactorial. This device compression does not correspond to worsening of aneurysm occlusion in all cases. However, it is apparent from our pilot study that a high arterial inflow effect is, at least, partially involved. Further theoretical and animal research studies are needed to increase our understanding of this phenomenon.

Authors contribution

JC: project development, data collection, manuscript writing, statistical analysis, approval of final version.

TY: project development, approval of final version.

CM, VDR, MI, LI, JM, LS: data analysis, approval of final version.

Disclosure of interest

LS and JM are consultants for Sequent Medical, TY is an employee of EBM corp.

Jildaz Caroff, Cristian Mihalea, Valerio Da Ros, Marta Iacobucci, Léon Ikka declare that they have no competing interest.

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    Remnants are described from completely occluded aneurysms and can even occur within a period of up to 3 years after treatment.20 They are mostly associated with a WEB shape modification in conjunction with a height reduction also referred to as “compression” of the device.16 Unfavorable wide-neck aneurysms and WEB undersize have been reported as a predisposing factors for a device compression, but the underlying mechanism remains unknown.20

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    Investigation of blood flow in large vessels with CFD is highly compatible with 4D-flow MRI, which can directly capture changes in the flow structure in an unsteady state. Some studies have evaluated hemodynamic changes after treatments [41–45], whereas others have used complementary CFD and 4D-flow MRI [42,46,47]. Here, we introduce blood flow studies on aortic dissection and pulmonary hypertension.

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    Mechanisms underlying WEB shape modifications are probably multifactorial. Caroff et al. [6] suggested that high arterial inflow could partially lay to device compression with a water-hammer effect. On the other hand, Pierot et al. suggested that this phenomenon could result from clot organization and clot retraction [7].

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