High-fidelity virtual stenting: modeling of flow diverter deployment for hemodynamic characterization of complex intracranial aneurysms

Abstract

Object: Flow diversion via Pipeline Embolization Device (PED) represents the most recent advancement in endovascular therapy of intracranial aneurysms. This exploratory study aims at a proof of concept for an advanced device-modeling tool in conjunction with computational fluid dynamics (CFD) to evaluate flow modification effects by PED in actual, treated cases.

Methods: The authors performed computational modeling of 3 PED-treated complex aneurysm cases. The patient in Case 1 had a fusiform vertebral aneurysm treated with a single PED. In Case 2 the patient had a giant internal carotid artery (ICA) aneurysm treated with 2 PEDs. Case 3 consisted of tandem ICA aneurysms (III-a and III-b) treated by a single PED. The authors' recently developed high-fidelity virtual stenting (HiFiVS) technique was used to recapitulate the clinical deployment process of PEDs in silico for these 3 cases. Pretreatment and posttreatment aneurysmal hemodynamics studies performed using CFD simulation were analyzed. Changes in aneurysmal flow velocity, inflow rate, wall shear stress (WSS), and turnover time were calculated and compared with the clinical outcome.

Results: In Case 1 (occluded within the first 3 months), the aneurysm had the most drastic flow reduction after PED placement; the aneurysmal average velocity, inflow rate, and average WSS were decreased by 76.3%, 82.5%, and 74.0%, respectively, whereas the turnover time was increased to 572.1% of its pretreatment value. In Case 2 (occluded at 6 months), aneurysmal average velocity, inflow rate, and average WSS were decreased by 39.4%, 38.6%, and 59.1%, respectively, and turnover time increased to 163.0%. In Case 3, Aneurysm III-a (occluded at 6 months) had a decrease by 38.0%, 28.4%, and 50.9% in average velocity, inflow rate, and average WSS, respectively, and turnover time increased to 139.6%, which was quite similar to Aneurysm II. Surprisingly, the adjacent Aneurysm III-b had more substantial flow reduction (a decrease by 77.7%, 53.0%, and 84.4% in average velocity, inflow rate, and average WSS, respectively, and an increase to 213.0% in turnover time) than Aneurysm III-a, which qualitatively agreed with angiographic observation at 3-month follow-up. However, Aneurysm III-b remained patent at both 6 months and 9 months. A closer examination of the vascular anatomy in Case 3 revealed blood draining to the ophthalmic artery off Aneurysm III-b, which may have prevented its complete thrombosis.

Conclusions: This proof-of-concept study demonstrates that HiFiVS modeling of flow diverter deployment enables detailed characterization of hemodynamic alteration by PED placement. Posttreatment aneurysmal flow reduction may be correlated with aneurysm occlusion outcome. However, predicting aneurysm treatment outcome by flow diverters also requires consideration of other factors, including vascular anatomy.

Keywords: CFD = computational fluid dynamics; FD = flow diverter; HiFiVS = high-fidelity virtual stenting; ICA = internal carotid artery; OphA = ophthalmic artery; PED = Pipeline Embolization Device; PICA = posterior inferior cerebellar artery; Pipeline Embolization Device; VA = vertebral artery; WSS = wall shear stress; computational fluid dynamics; flow diverter; high-fidelity virtual stenting; intracranial aneurysm; stent modeling; vascular disorders.

Figure 1

Case I: A fusiform VA aneurysm in a 66-year-old man—Angiograms at the initial pre-treatment and post-treatment 3-month follow-up imaging.

Figure 2

Case II: A wide-based supraclinoid ICA aneurysm in a 65-year-old woman—Angiograms at the initial pre-treatment and post-treatment 9-month follow-up imaging.

Figure 3

Case III: Tandem ICA aneurysms in a 45-year-old woman—Angiograms for the initial pre-treatment and post-treatment 3-, 6-, and 9-month follow-up imaging.

Figure 4

Pre- and post-treatment hemodynamics in Case I. A. Aneurysm model without and with PED deployment; B. 3D streamlines; C. Intra-aneurysmal velocity vectors on a representative plane; D. WSS distributions. I(U): Untreated. I(T): Treated by 1 PED.

Figure 5

Quantitative comparison of PED-induced flow reduction in relation to the occlusion outcome in the four aneurysms. A. Average aneurysmal velocity reduction; B. Aneurysmal inflow rate reduction; C. Average aneurysmal WSS reduction; D. Relative aneurysmal turnover time. Symbols I, II(T2), III-a and III-b denote modeling results of the actual treatment in Aneurysms I, II, III-a and III-b, respectively. Note that Aneurysm III-b had blood drainage to the ophthalmic artery. Symbol II(T1) denotes hypothetical results of Aneurysm II treated by the first PED only to see how much additional flow diversion was induced by adding the second PED.

Figure 6

Pre- and post-treatment hemodynamics in Case II. A. Aneurysm model without and with PED deployment; B. 3D streamlines; C. Intra-aneurysmal velocity vectors on a representative plane; D. WSS distributions. II(U): Untreated. II(T1): Treated by 1 PED (hypothetical). II(T2): Treated by 2 PEDs.

Figure 7

Pre- and post-treatment hemodynamics in Case III. A. Tandem aneurysm model without and with PED deployment; B. 3D streamlines; C. Intra-aneurysmal velocity vectors on a representative plane; D. WSS distributions. III(U): Untreated Aneurysm III-a and III-b; III(T): Aneurysm III-a and III-b treated by a single PED.