Abstract
The cervical aortic arch is a rare congenital vascular abnormality related to the anomalous development of the aortic arch. We present the case of a 6-year-old patient with a large aneurysmal cervical aortic arch who underwent surgical correction and arch reconstruction. Surgical repair was indicated based on the risk of progressive dilation and rupture, aiming to restore correct geometry and hemodynamics. We evaluated preoperative and postoperative hemodynamics using computational fluid dynamics simulations, and we also identified, within the repaired region, an area that remains affected by greater turbulent flow, requiring follow-up surveillance.
Case Presentation
The cervical aortic arch (CAA) is a rare congenital vascular abnormality related to the abnormal embryological development of the aortic arch. Various forms range from vascular rings to large aneurysmal formations. 1 We present a rare case of a 6-year-old CAA patient with a large arch aneurysm in the left upper chest. The diagnosis was made at birth and the patient was followed because the child was asymptomatic. At age 6, she underwent a computed tomography angiography (CTA) scan, which showed a normal brachiocephalic trunk and left carotid artery with a tortuous and aneurysmal distal aortic arch occupying the left upper part of the chest cavity. The left subclavian artery originates from the end of the aneurysm (Figure 1). The surgical repair consisted of an aneurysmal resection and terminal-lateral anastomosis with an anterior autologous patch and left subclavian artery reimplantation in the ascending aorta with the interposition of a Dacron tube graft.
Figure 1.
Comparison between preoperative (A, green-dashed circle) and postoperative image reconstructions (B, blue-dashed circle).
After 7 months, the patient underwent postoperative follow-up CTA that showed a widely patent arch that was well reconstructed geometrically with severe stenosis of the reimplanted subclavian artery. However, such stenosis did not affect perfusion, since there was good vascular compensation through the left vertebral artery.
Computational Fluid Dynamics Hemodynamic Simulations
We compared preoperative and postoperative flows using the computational fluid dynamics (CFD) method to assess whether the restoration of almost normal aortic arch geometry corresponded to better hemodynamic conditions. Three-dimensional (3D) patient-specific models were created by segmenting preoperative and postoperative CTA images using Mimics Medical 25.0 software (Materialise). The same transient inflow and outlet Boundary Conditions (BCs) were used in both models. The inflow was described by a parabolic flow profile with a cardiac output of 85 mL/s; outlet BCs at the supra-aortic trunks and descending aorta were described by the 3-element Windkessel model according to the literature reference. 2 Blood was modelized like a Newtonian fluid with 1.06 g/cm3 of density, and 0.04 g/(cm/s) of viscosity. We use the open-source software SimVascular (https://simvascular.github.io/) as a CFD solver. To evaluate the flow characteristics, we studied streamlines and particle tracking.3,4 Subsequently, we compared the washout of the descending aorta and the supra-aortic arteries. Finally, we evaluated the pressure drop (ΔP) between the inlet of the aneurysm (proximal section) and the outlet of the aneurysm (distal section), the oscillatory shear index (OSI), and the time average wall shear stress (TAWSS).
Results
The CFD analysis revealed improvement in postoperative fluid dynamics compared with the preoperative. The postoperative streamlines were less helical than the preoperative model (Supplemental Video1). Particle stagnation (Figure 2A) disappeared after surgery (Supplemental Video2) due to the improvement in particle washout in the aneurysm. Before surgery, most of the particles were diverted into the supra-aortic arteries with few reaching the descending aorta. The pressure gradient through the aortic arch decreases from ΔPpre of 33 to a 3 mmHg ΔPpost. In conclusion, CFD showed an overall improvement in the hemodynamics of the aortic arch after repair. However, the postaneurysm zone showed the persistence of abnormal hemodynamic factors (Figure 2B). We found an increase in the percentage of the surface of the aorta wall affected by a high OSI (2% vs 24%) and low TAWSS (5% vs 21%), at the sutured stump of the resected aortic arch. The combination of elevated OSI (OSI > 0.2) 5 with low TAWSS (<10dyne/cm2), 6 that are triggers for adverse remodeling of the aortic wall, causes tissue inflammation that will in the long term alter the aortic wall.7,8
Figure 2.
(A) Comparison of particle-tracking in preoperative and postoperative anatomy; each frame corresponds to a time instant in the cardiac cycle (T1: early systole; T2: systolic peak; T3: early diastole; T4: late diastole). (B) The percentage of high OSI and low TAWSS increase in the postsurgery model. Percentages refer to aneurysm area. Abbreviations: OSI, oscillatory shear index; TAWSS, time average wall shear stress.
Summary
We described a rare case of a 6-year-old patient with an aneurysmal CAA in which we applied CFD simulations to quantify how surgical repair normalized aortic arch hemodynamic by comparing preoperative with postoperative anatomy. The CFD simulation showed that surgical repair reestablished near-normal fluid dynamics within the reconstructed aortic arch. Interestingly, thanks to fluid dynamics simulation, we found an aortic region related to surgical repair that remains affected by altered fluid dynamic forces. Although it is well accepted that restoration of normal anatomy implies restoration of normal flow characteristics, it cannot be forgotten that some areas may remain affected by turbulent flow and therefore be at risk of adverse remodeling. These areas can be shown only with the use of CFD evaluation, revealing which aortic segment requires detailed long-term surveillance. This single case report highlights the importance of integrating novel biomechanical tools in clinical scenarios to better understand the care needed for rare diseases.
Supplemental Material
Video 1. Pre-operative and postoperative streamlines.
Video 2. Pre-operative and postoperative particle tracking.
Acknowledgments
The authors would like to extend their sincere thanks to the patient and his parents for their cooperation in the study.
Footnotes
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The authors received the following financial support for the research, authorship, and/or publication of this article: This work was supported by IRCCS Policlinico San Donato, a Clinical Research Hospital partially funded by the Italian Ministry of Health.
ORCID iDs: Serena Anglese https://orcid.org/0000-0002-7423-9757
Mauro Lo Rito https://orcid.org/0000-0002-3175-3764
Supplemental Material: Supplemental material for this article is available online.
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Supplementary Materials
Video 1. Pre-operative and postoperative streamlines.
Video 2. Pre-operative and postoperative particle tracking.