A Case of Anastomotic Aneurysm after Superficial Temporal Artery–Middle Cerebral Artery Bypass for Moyamoya Disease Treated with Coil Embolization

Abstract

Objective: Formation of an aneurysm at the anastomosis site is a rare complication of superficial temporal artery–middle cerebral artery (STA-MCA) bypass for moyamoya disease (MMD). All 5 previously reported cases were treated with craniotomy, and no case of endovascular treatment has been reported to date. Here, we report a case in which endovascular treatment was performed for an anastomotic aneurysm that developed after STA-MCA bypass surgery for MMD.

Case Presentation: A 46-year-old woman with no relevant medical history developed a cerebral hemorrhage and was diagnosed with MMD. Bilateral STA-MCA bypass was performed to prevent recurrence of bleeding, and a de novo aneurysm was found at the right anastomosis site 1 year after the surgery. After a 2-year follow-up period, the size of the aneurysm and the diameter of the STA increased; therefore, treatment was initiated. Endovascular treatment was performed using the double-catheter technique. After coil embolization, the aneurysm was no longer visible, and no complications were observed.

Conclusion: Anastomotic aneurysms after STA-MCA bypass can be safely and effectively treated with endovascular therapy.

Introduction

Superficial temporal artery–middle cerebral artery (STA-MCA) bypass surgery has been developed as a surgical treatment for occlusive cerebrovascular disorders and is frequently used in cases of moyamoya disease (MMD) to improve cerebral blood flow, thereby preventing ischemic symptoms or recurrent bleeding.¹⁾ The formation of an aneurysm at the anastomosis site is a rare complication of STA-MCA bypass surgery. Once an anastomotic aneurysm ruptures, it can cause subarachnoid or cerebral hemorrhage, resulting in serious conditions in some cases.^2,3) Clipping, wrapping, and aneurysmectomy combined with bypass have been reported as treatments for management of anastomotic aneurysms. However, in the case of MMD, indirect anastomosis develops from the dura and fascia around the anastomosis site; thus, direct surgery may injure these collateral circulations.

Herein, we report a case of a patient who was effectively treated with coil embolization for a de novo anastomotic aneurysm that developed 1 year after STA-MCA bypass surgery for MMD.

Case Presentation

The patient was a 46-year-old woman with no relevant medical history. She visited a local doctor for headaches and was diagnosed with a left thalamic hemorrhage on head CT (Fig. 1A). The patient was referred to our hospital for treatment. On arrival at our hospital, she had no disturbance of consciousness and no neurological abnormalities. The patient was diagnosed with MMD on DSA (Fig. 1B and 1C), and bleeding from the collateral arteries due to MMD was considered. Therefore, bypass surgery was planned to prevent rebleeding. First, a left STA-MCA bypass surgery was performed, and thereafter a right STA-MCA bypass surgery was performed. Postoperative MRA showed that bilateral STA-MCA bypasses were patent (Fig. 2A), and the patient was discharged without any complications.

Fig. 1 Head CT (A) and the anteroposterior views of the right (B) and left (C) common carotid arteries on DSA at the onset of cerebral hemorrhage. Head CT reveals left thalamic hemorrhage. DSA reveals a stenosis of the terminal parts of both internal carotid arteries, loss of the anterior and middle cerebral arteries, and the development of moyamoya vessels. Lt, left; Rt, right

Fig. 2 MRI performed after right superficial temporal artery–middle cerebral artery bypass surgery (A), 1 year later (B), and 3 years later (C). A de novo aneurysm is seen at the anastomosis in B (white arrow), and a superficial temporal artery dilation is seen in C (thick arrow).

MRI 1 year after the right-sided surgery revealed a de novo aneurysm at the anastomosis. At that point, because the aneurysm was not large, we decided to observe the patient (Fig. 2B). The STA diameter at that time was approximately 1 mm. MRI performed 2 years later showed that the aneurysm had become larger; furthermore, the diameter of the STA had increased. DSA revealed that the aneurysm was located on the MCA side of the STA-MCA anastomosis and was wide-necked, measuring 4 × 3.5 mm with a neck diameter of 4 mm. The STA had expanded to a diameter of 2 mm (Fig. 3). It was thought that expansion of the STA would increase blood flow to the aneurysm more than before, which could cause the aneurysm to grow larger or rupture in the future; therefore, we decided to treat the aneurysm. The presence of indirect anastomoses from the middle meningeal artery (MMA) toward the MCA regions and the anterior cerebral artery regions, respectively, was confirmed on DSA (Fig. 3A and 3B). To avoid damage to these collateral blood vessels while performing a craniotomy, endovascular treatment was chosen as the most suitable treatment method. Because this was a wide-necked aneurysm with a narrow depth, it was expected to be difficult to treat with coil embolization without any adjunctive technique. Therefore, we decided to treat it with the double-catheter technique.

Fig. 3 Anteroposterior (A) and lateral (B) images of the right common carotid artery on DSA, and a 3D rotational angiography image (C) performed 3 years after bypass surgery. Superficial temporal artery dilation (thick arrow) and a wide-neck aneurysm (solid arrow) located on the contralateral side of the anastomosis are observed. The open arrow shows the middle cerebral artery. The middle cerebral artery region (black arrow) is contrasted from a branch of the middle meningeal artery (arrowheads), and the anterior cerebral artery region (double arrows) is contrasted from the distal end of the middle meningeal artery (open arrowheads).

Endovascular treatment

Two weeks before treatment, the patient began taking 100 mg aspirin and 75 mg clopidogrel. Treatment was performed under local anesthesia and conscious sedation. After systemic heparinization following sheath insertion, a 6-Fr Slimguide (Medikit, Tokyo, Japan) was advanced into the right external carotid artery. Because the aneurysm had a wide neck and shallow depth (3.5 mm), we performed the double-catheter technique as planned. An Excelsior SL-10 (Stryker, Kalamazoo, MI, USA) was introduced into the STA using a 0.014-inch microguidewire (CHIKAI 14; Asahi Intecc, Aichi, Japan), and no decrease in STA blood flow was observed. Subsequently, a Headway Duo (Terumo, Tokyo, Japan) was guided to the STA in the same fashion, and blood flow in the STA was good. An Excelsior SL-10 and Headway Duo were placed into the aneurysm, and coils were inserted through each catheter (Fig. 4A and 4B). The coil frame was created using a 3 mm × 4-cm Avenir Complex Framing (Wallaby Medical, Shanghai, China) and a 3 mm × 6-cm Target 3D (Stryker). Subsequently, 2 coils—2 mm × 2.5-cm Target Tetra (Stryker) and a 1.5 mm × 2-cm Avenir Complex PICO (Wallaby Medical)—were inserted, and almost complete occlusion was achieved (Fig. 4C). The STA-MCA bypass was confirmed to be patent.

Fig. 4 DSA images taken from a guiding catheter placed into the right external carotid artery during coil embolization. A, B: No decrease in blood flow is observed when the 2 microcatheters are guided to the superficial temporal artery. C: DSA image taken at the end of coil embolization.

Diffusion-weighted imaging performed postoperatively showed a small, high-intensity signal in the right parietal region, but this was found to be asymptomatic. The patient was discharged on the 5th postoperative day as per routine schedule. MRI performed 1 month and 6 months later showed that the aneurysm was completely occluded, and the STA-MCA bypass was fully patent. However, there is a possibility that the aneurysm may recur in the future, and thus regular follow-up will be performed.

Discussion

We report a case of successful endovascular treatment using the double-catheter technique via the STA for an anastomotic aneurysm after STA-MCA bypass. To our knowledge, there are no reports of catheter-based treatment for anastomotic aneurysms after direct bypass for MMD. There have been several reports of anastomotic aneurysms after STA-MCA bypass surgery^2,3); however, only 5 cases of MMD have been reported.^4–8) Craniotomy was performed in all 5 cases, with clipping in 4 and aneurysmectomy in 1 case. Eguchi et al. reported that anastomotic aneurysms after STA-MCA bypass for MMD can be safely treated with craniotomy by minimizing the rotation of the dura mater.⁸⁾ However, in MMD, indirect anastomosis develops from the dura and fascia around the anastomosis site after STA-MCA bypass surgery, and these collateral vessels are responsible for blood flow to the brain. In this case, the presence of an indirect bypass could be confirmed via the MMA. Therefore, we decided to first attempt endovascular treatment, which is also minimally invasive.

As the internal carotid artery (ICA) becomes stenotic owing to the progression of MMD, an approach from the ICA is difficult, and an approach from the STA remains the only option. A previous case report described a successful endovascular approach from the STA for an anastomotic aneurysm that developed after STA-MCA bypass in a patient with symptomatic chronic carotid artery occlusion.⁹⁾ In that report, stent-assisted coiling was performed, and 1 microcatheter was guided through the enlarged STA after direct bypass surgery during stent placement and another during coil embolization; the approach was possible without spasm or difficulty in navigation. Embolization using a stent was also considered; however, we did not choose stent-assisted coiling because we wanted to avoid placing a stent at the anastomosis. Moreover, the angle from the STA to the MCA was steep (less than 90°). Another case report describes coiling via the dilated MMA to treat a pseudoaneurysm that developed in the MMA after indirect bypass surgery in a patient.¹⁰⁾ In the present case, the STA was dilated after direct bypass surgery and the microcatheter could be guided without any problems. Regarding the method of embolization of the aneurysm, we chose to treat it with the double-catheter technique because of its wide neck. There have been no previous case reports of the use of the double-catheter technique to treat an anastomotic aneurysm, and to our knowledge, ours is the first study to report this. In our case, the 2 microcatheters were guided into the STA. Careful attention must be paid to the occurrence of ischemic complications owing to reduced blood flow in the STA. Therefore, we guided only 1 microcatheter into the aneurysm and ensured that there was no stagnation of blood flow in the STA before introducing the 2nd catheter. Based on this case and previous reports, coil embolization can be considered an effective treatment for anastomotic aneurysms. However, if the STA is significantly tortuous, catheter guiding may be challenging. Care must be taken when inserting a catheter into the STA to avoid vasospasm. Choosing to perform endovascular treatment and selection of an adjunctive technique must be considered on a case-by-case basis, depending on the diameter, tortuosity, course of the STA and the shape of the aneurysm.

Hemodynamic stress at the anastomotic site is thought to be a cause of anastomotic aneurysms. Kohno et al. speculated that the artificial branch formed by the STA-MCA bypass was exposed to excessive jet flow from the enlarged STA, resulting in fusiform-shaped dilation at the anastomosis site and aneurysm formation.³⁾ In this case, the STA had clearly enlarged in diameter compared to that before the STA-MCA bypass surgery, and the aneurysm protruded toward the MCA wall, where blood flowed from the STA. A report of 5 cases of anastomotic aneurysms in MMD showed that 2 cases presented with bleeding, and 3 were asymptomatic and discovered incidentally. The prognosis was poor in the 2 cases in which bleeding occurred and good in the 3 asymptomatic cases. If bleeding occurs, there is a high possibility of disability, and if the hematoma is large, craniotomy or endoscopic surgery is necessary, which may damage the indirect anastomosis. The optimal timing for therapeutic intervention when an anastomotic aneurysm is detected has not yet been determined. It is recommended that treatment should be considered based on the size of the aneurysm, the possibility of growth, and increases in STA diameter. The longest reported time to onset is 20 years after STA-MCA bypass surgery, indicating that long-term follow-up after surgery is necessary.⁴⁾

Conclusion

Here, we report a case of endovascular treatment of a rare de novo aneurysm at the direct bypass anastomosis site of the MMD. There are no similar case reports, and coil embolization is the most suitable treatment in such cases.

Informed Consent and Consent to Publish

Informed consent was obtained from the participant included in the study. The participant has consented to the submission of this case report to the journal.

Disclosure Statement

The authors declare that they have no conflicts of interest.

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