Rare case of de novo anastomotic site aneurysm after anterior cerebral artery side-to-side bypass: curative treatment with superficial temporal artery interposition graft-assisted trapping and etiological analysis. Illustrative case

Abstract

BACKGROUND

De novo aneurysms occurring at the anastomotic site are extremely uncommon, especially following side-to-side (STS) bypass for anterior cerebral artery (ACA) revascularization. Their etiology remains uncertain; however, it is believed to be related to hemodynamic shear stress and inherent vascular fragility, potentially linked to genetic anomalies. Furthermore, surgical intervention is mandatory to avert aneurysm growth or rupture.

OBSERVATIONS

A 38-year-old-male first presented with a large fusiform aneurysm of the left distal ACA and underwent ACA-ACA STS bypass with aneurysm excision. Nonetheless, the de novo aneurysm was discovered to arise at the bypass site 7 months after the operation. Subsequently, a strategic radical intervention was performed. At the 26-month follow-up, the patient’s modified Rankin Scale score was 0, and there was good bypass patency without aneurysm recurrence. The aneurysm formation was attributed to the fragility of the underlying arterial wall, which might be aggravated by STS bypass as evidenced by the histological findings and computational fluid dynamics (CFD) analysis.

LESSONS

The revascularization strategy must be executed cautiously given the existence of wall disease, which poses a risk for aneurysm formation, particularly following modification by STS bypass, as demonstrated by CFD and histological findings. Careful monitoring and long-term vascular assessment are crucial.

https://thejns.org/doi/10.3171/CASE25100

De novo aneurysms arising at the anastomotic site are exceedingly rare,^1–3 particularly following anterior cerebral artery (ACA) side-to-side (STS) bypass. There is only one previously reported case of this occurrence in the literature.² Most de novo aneurysms arise at the site of the superficial temporal artery (STA)–middle cerebral artery (MCA) bypass after an end-to-side anastomosis technique.^1,3–15 The definite etiology is still unknown, yet it is believed to be attributed to hemodynamic shear stress, inherent vascular fragility, and surgical manipulation.³ Prompt diagnosis and treatment are crucial since a ruptured de novo aneurysm can lead to devastating consequences.^3,6,8,10 Here, we present our unique case of a de novo aneurysm arising at the ACA-ACA STS bypass site along with a computational fluid dynamics (CFD) study and histological results.

Illustrative Case

A 38-year-old male presented with a 10-mm incidental distal ACA aneurysm (Fig. 1A). He had a family history of an aortic aneurysm and cerebral aneurysm in first- and second-degree relatives, respectively. The first operation was performed by ACA-ACA STS bypass distal to the aneurysm and reimplantation of the left callosomarginal artery (CMA) to the left pericallosal artery (PcaA) using a short STA inter­position graft (Video 1). Then, the aneurysm was completely excised (Fig.1B–E). The histopathological results showed severe fragmen­tation of the internal elastic lamina, fibrous thickening and sclerotic changes of the tunica media, and loss of smooth muscle, which is consistent with chronic dissection. The patient tolerated the procedure well without complications, and follow-up CT angiography (CTA) at 1-month postoperatively showed bypass patency without aneurysm recurrence (Fig. 1F). Unfortunately, an 11-mm de novo aneurysm arising at the STS bypass site was found at 7 months postoperatively (Fig. 1G).

FIG. 1.

A: Preoperative CT angiogram showing a large fusiform aneurysm at the left A2–3 segment incorporated with the left CMA. B and C:Intraoperative findings. An A3-A3 side-to-side bypass was performed distal to the aneurysm (B). The left CMA (arrow) was reimplanted to the left PcaA (arrowhead) using a short STA interposition graft (C; asterisk). D and E:Preoperative (D) and postoperative (E) schematic drawings of the procedure. F and G: Postoperative CT angiograms. At 1-month follow-up, bypass patency was noted without aneurysm recurrence (F). At the 7-month follow-up, the recurrent aneurysm (arrow) was found at the bypass site next to the previous aneurysm location with involvement of the left distal pericallosal artery (G; arrowhead).

Video 1. Video demonstrating the surgical treatment. In the first operation, we performed an ACA side-to-side bypass, reimplantation of the left CMA, and trapping of the aneurysm. Click here to view.

After discussion with the patient, he opted to undergo a second surgery. Complete aneurysm eradication and revascularization of the bilateral ACAs were planned (Video 2). Following a right unilateral interhemispheric approach, the 3 end-to-side anastomoses using free Y-shaped STA graft were performed at the right PcaA and left middle internal frontal artery as the recipients, with the right CMA as the donor artery. Consequently, the aneurysm and microscopically abnormal vessel were included in the trapping procedure (Fig.2). The patient recovered well without any neurological deficits.

FIG. 2.

Intraoperative findings of the second operation. A: Three end-to-side anastomoses were performed distal to the aneurysm (black asterisk) using a Y-shaped superficial temporal artery graft (white asterisk) to the right callosomarginal artery (white arrow), right PcaA (white arrowhead), and left PcaA (black arrowhead). B: Indocyanine green videography showing bypass patency without the aneurysm seen. C and D:Preoperative (C) and postoperative (D) schematic drawings of the procedure.

Video 2. Video demonstrates the second operation, where an in situ bypass using a free Y-shaped STA interposition graft to the bilateral distal ACAs and the right CMA was performed. The aneurysm was subsequently excised after complete trapping. Click here to view.

The histological results showed chronic inflammation and loss of the internal elastic lamina and smooth muscle, which were the same findings in the first operation (Fig. 3). The patient’s modified Rankin Scale score at the 26-month follow-up was 0 without aneurysm recurrence. Additionally, CTA and MRI showed bypass patency and no infarction, respectively (Fig. 4). Immediately after the first STS bypass, CFD analysis demonstrated a localized area with high wall shear stress along the front wall of the anastomosis between the bilateral A3 segments with the flow pulsation magnitude (Fig.5A and B). At 7 months postoperatively, CFD showed increased flow pulsation and wall shear stress also concentrated at the frontal wall of the aneurysm (Fig. 5C and D). At the 26-month follow-up, CFD demonstrated a significant decrease in wall shear stress and flow pulsation at the anastomotic sites with good patency of the Y-shaped STA interposition graft (Fig. 5E and F).

FIG. 3.

Histopathological findings of the aneurysm excised from the first operation. A: H&E staining demonstrating loss of smooth muscle and a thin aneurysm wall (arrowheads). B: Elastica van Gieson staining showing fragmentation of internal elastic lamina (arrowheads). Histopathological findings from the second operation. C and D: Elastica H&E and Elastica van Gieson staining demonstrating loss of smooth muscle, and internal elastic lamina (arrowheads) with thin aneurysm wall and organized thrombus in the aneurysm sac (asterisk), respectively. Original magnification ×40 (A, C, and D); ×200 (B).

FIG. 4.

Postoperative follow-up imaging at 26 months postoperatively. A:CT angiogram demonstrating bypass patency (arrow) without aneurysm recurrence. B: Diffusion-weighted MR image showing no cerebral infarction.

FIG. 5.

CFD study. A and B: Immediately after the first operation, the regional high wall shear stress was noted at the front wall of the anastomosis along with flow pulsation (arrow). C and D: At 7 months following the surgical procedure, the flow pulsation and wall shear stress were notably concentrated at the frontal wall, accompanied by the formation of a de novo aneurysm (arrowheads). E and F: Patency of the Y-shaped interposition graft (arrow) and a significant decrease in wall shear stress and flow pulsation at the anastomotic sites (arrowheads) at the 26-month follow-up.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

We reported an exceedingly rare case of a de novo aneurysm fol­lowing the STS bypass for ACA revascularization. To our knowledge, this is the first report of the STS anastomotic de novo aneurysm, wherein a comprehensive examination of potential risks is demon­strated by both the CFD study and histological findings. Additionally, this is the first study to compare the CFD analysis of the STS and end-to-side bypass. We also delineated our unique surgical strategies, encompassing complex bypass procedures for curative treatment.

De Novo Aneurysms Following STS Bypass

To our knowledge, there are only 2 cases, including ours, of an aneurysm occurring after STS bypass in the distal ACA. Most reported cases of de novo aneurysms were steno-occlusive diseases treated with an extracranial-intracranial bypass.^{1–3,5–14,16–18} The aneurysm was discovered between 25 days and 27 years after the first operation, with 9 of 21 reported cases (42.9%) presenting with rupture. Six of these 9 cases (66.7%) were noted as having poor outcomes. Endo et al.² reported the first case of a de novo aneurysm arising at the site of an A3-A3 STS bypass. Their CFD study revealed high wall shear stress at the front wall of the anastomosis site, where the aneurysm was harbored, which corresponds to our CFD results.

The potential causes are inherent vascular fragility and hemody­namic stress. In addition, a history of an intracranial dissecting aneu­rysm could be associated with a de novo aneurysm due to the vessel’s wall fragility, which is easily triggered by the surgical manipulation. Several authors have reported histopathological findings to ascertain the true causes of de novo aneurysms, where the presence of pseu­doaneurysms were previously suggested to be related to traumatic or surgery-associated dissecting aneurysms.^5,6,8,18 However, the fea­ture of intimal dissection itself could particularly indicate the presence of a preexisting wall disease.¹⁹ In our case, the pathological vessel wall at the anastomotic site was observed microscopically during the initial surgical procedure. Moreover, the histopathological analysis of the excised aneurysms from both the initial and subsequent surgical procedures revealed consistent findings, characterized by chronic inflammation accompanied by the degeneration of the internal elas­tic lamina and smooth muscle. This demonstrated that there was a preceding pathologic vessel wall at the location where the bypass was conducted.¹⁹ Notably, both cases of aneurysms arising at the STS bypass site (including ours) had preexisting dissecting aneu­rysms, which could potentially be the underlying condition that causes aneurysm formation.^2,19 As a result, our findings support those of Endo et al.,² indicating that the STS bypass might pose a risk for aneurysm formation, particularly when conducted in the presence of anomalous arterial wall pathology.

In recent years, somatic mutations have been reported in intra­cranial aneurysms. Notably, fusiform-shaped aneurysms have been linked to genetic abnormalities related to the NF-κB signaling pathway, including PDGFRB mutations, even when the aneurysms are relatively small.¹⁹ As these mutated pericytes migrate from the adventitia to the intimal layer, the aneurysms can progress from small to large in size. In the current case, the initial surgery involved performing an STS bypass on a pathologic vessel that appeared microscopically white and already showed early signs of aneurysmal changes. Therefore, during the second surgery, all vessels that appeared pathological under the microscope were included in the trapping procedure to mini­mize the risk of further recurrence.

Surgical Treatment and Revascularization Strategy

We planned to trap the aneurysm including all microscopically abnor­mal vessel walls that could be pathologic and recur. Consequently, to maintain the bilateral distal ACA flow, revascularization of the bilateral ACA is mandatory.²⁰ The diameter discrepancy between PcaAs and the aneurysm affecting the left PcaA, as well as the distance between the donor and recipient arteries, led to the decision for bypass using an interposition graft between distal ACA branches. Furthermore, due to the inversion of the STS back wall intima, which elevates the risk of thrombosis, we preferred an end-to-side bypass instead of an STS bypass.²¹ The rationale of flow dynamics indicates that the end-to-side bypass results in less wall shear stress at the anastomotic site in comparison with STS bypass, as evidenced by our CFD analysis. Given the size of the right CMA, we believed that it could adequately supply the bilateral ACA without the need for an additional extracranial-intracranial bypass.^2,20,21 Accordingly, we used the interposition graft to ensure bidirectional flow to the bilateral ACAs, which involves 3 end-to-side anastomoses.² Several authors have reported using more complex techniques in bilateral ACA revascularization with a radial arterial graft;^22,23 however, we chose the STA because it can be harvested through the same incision and is a compatible size to distal ACA.²¹ One drawback is scalp complications,²⁴ which were not present in our case. Endovascular treatment has disadvantages since the aneurysms were of fusiform morphology and located distally. Furthermore, stent-assisted coil embolization or a flow diverter has limitations of navigation and device size in such a distal location and the necessity of antiplatelet therapy in cases in which surgical man­agement is required.

Limitations

The natural history and true incidence of these complex aneurysms remain not well understood, and we believe that they are underreported in the existing literature. Larger cohorts of these specific populations and long-term follow-up are mandatory for comprehensive study, combining flow dynamics, histological, and genetic evaluations.

Lessons

We highlight that the existence of arterial wall disease requires a cautious approach to the revascularization strategy, as it poses the risk of aneurysm formation, particularly following the STS bypass tech­nique. This assertion is supported by CFD and histological findings, despite the limited number of reported cases on this subject matter. Furthermore, we exhibited an effective radical treatment with complete aneurysm removal accompanied by an STA interposition graft for the revascularization of the ACA region.

The rationale for our favorable outcome is that the end-to-side suturing technique might offer preferable flow dynamics compared with the STS bypass, where the intima results in an everted position on the front wall and an inverted position on the back wall, poten­tially increasing shear stress on the front wall of the anastomosis. This process may exacerbate aneurysm formation in the parent artery with preexisting wall pathology. As previously stated, we advocate for the utilization of an interposition graft with an end-to-side anas­tomosis technique instead of the STS bypass in cases in which there is a heightened risk due to preexisting arterial wall pathology, such as arterial dissection or chronic inflammation resulting from severe atherosclerosis.²⁵

Acknowledgments

Gahn Duangprasert is a fellow of the Takeda Science Foundation. Sergi Cobos Codina is a fellow of the Alfonso Martín Escudero Foundation. We extend our gratitude to Mr. Ito Kouhei, the radiologist at Sapporo Teishinkai Hospital, for his excellent computational fluid dynamics analysis.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Tanikawa, Duangprasert, Cobos Codina. Acquisition of data: Duangprasert, Hermanto. Analysis and interpretation of data: Duangprasert, Cobos Codina. Drafting the article: Tanikawa, Duangprasert. Critically revising the article: Duangprasert, Ota, Hermanto, Cobos Codina. Reviewed submitted version of manuscript: Tanikawa, Duangprasert, Ota, Hermanto, Cobos Codina. Approved the final version of the manuscript on behalf of all authors: Tanikawa. Administrative/technical/material support: Tanikawa, Duangprasert, Ota, Cobos Codina. Study supervision: Tanikawa, Ota, Noda.

Supplemental Information

Videos

  Video 1. https://vimeo.com/1072560657.

  Video 2. https://vimeo.com/1072562379.

Correspondence

Rokuya Tanikawa: Stroke Center, Sapporo Teishinkai Hospital, Sapporo, Hokkaido, Japan. superbypass@gmail.com.