Endovascular treatment of A1 aneurysms of the anterior cerebral artery
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.185405
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study was to present the clinical and angiographic outcomes of A1 aneurysms treated by coil embolization.
Keywords: Aneurysm; anterior cerebral artery; endovascular treatment; subarachnoid hemorrhage
A1 segment aneurysms are rare lesions located between the bifurcation of the internal carotid artery (ICA) and the anterior communicating artery, with an incidence of 0.59%–4%.,,,,, Aneurysms in this location usually result in either subarachnoid hemorrhage or cerebral infarction. According to their morphology and pathology, A1 segment aneurysms can be defined as saccular or dissecting aneurysms. Previous data revealed that most of the A1 aneurysms were saccular; nontraumatic dissecting aneurysms located at the A1 segment were rarely reported.,
In addition, A1 aneurysms usually have some unique characteristics such as a small size and fragility and their management is often complicated due to their complex anatomy or associated vascular anomalies.,,, Moreover, A1 aneurysms have some distinctive configurations and may be in close proximity to perforators or branch vessels,,,, which makes them challenging to treat.
In this study, we report our experience with 38 cases of A1 aneurysm (20 ruptured and 18 unruptured) treated by an endovascular approach in our hospital. The endovascular treatment selection and clinical follow-up outcomes are also discussed.
The study protocol was approved by the research ethics committee at Beijing Tiantan Hospital; formal written consent was obtained from all the patients. From January 2011 to August 2014, we retrospectively collected the angiographic and clinical records of 38 consecutive patients (1.7%, 38/2192) with A1 aneurysms who received endovascular treatment at our institution. Among the 38 patients who underwent successful endovascular treatment, there were 12 men and 26 women with a mean age of 53.8 ± 11.9 years (range, 20–76 years); 18 patients had incidental aneurysms, and 20 had subarachnoid hemorrhage (SAH). Hunt and Hess grade I was observed in 16 patients, grade III in 3 patients, and grade IV in 1 patient.
We collected and reviewed the patient demographics (age, gender, etc.); aneurysmal status (ruptured versus unruptured at presentation) and type (saccular or dissecting); morphologic characteristics of the aneurysm (the maximum diameter of the aneurysm at the dome and neck, dome-to-neck ratio [DNR], and location); treatment options; treatment results; as well as the follow-up outcomes. We classified the patients into two groups (ruptured group and unruptured group). The clinical and angiographic differences between the ruptured group and unruptured group were compared and analyzed.
According to the angiographic features on digital subtraction angiography (DSA), we further classified the A1 aneurysms as being in the proximal one-third (those near the internal carotid artery [ICA] bifurcation), distal one-third (those in proximity to the anterior communicating artery [AComA]), and middle one-third segment aneurysms (those present between the proximal and the distal segments). Besides, perforators related to the aneurysm were carefully observed and recorded. Three-dimensional (3D) digital subtraction angiography (DSA) was used to locate the origin of the aneurysms on the circumference of A1, and their direction was classified as superior, inferior, anterior, and posterior. The diagnosis of a dissecting aneurysm was confirmed by the angiographic features on DSA, including a narrowed irregular or segmental stenosis, irregular fusiform or aneurysmal dilation, and retention of the contrast agent.,,
Indication for endovascular treatment was assessed for every patient by two experienced interventional neuroradiologists (M. Lv and X. Lv).
General anesthesia was utilized in all cases. An Echelon-10 microcatheter (ev3) or Headway 17 microcatheter (Microvention) was used for coiling. To achieve effective and stable positioning in the aneurysm sac, a steam “C-shaped,” “S-shaped,” or “preshaped 45°” microcatheter tip was preferred. In one case, a retrograde approach from the contralateral ICA through the AComA was performed. Undetachable balloon (HyperForm, ev3) was used in one case. The Enterprise stent (Codman Neurovascular, Miami Lakes, FL, USA) or Solitaire stent (Solitaire AB neurovascular devices, eV3, Inc., Irvine, CA, USA) was used for wide-necked (>4 mm or dome/neck ratio <2) or complex aneurysms.
For patients with a dissecting aneurysm, we preferred the parent vessel occlusion [Figure 1]. This decision was made, after evaluation of the collateral supply of the anterior cerebral artery (ACA) from the contralateral carotid artery, by Mata's test or balloon-test occlusion.
According to the size and shape of the aneurysm, appropriate coils were selected. We inserted the coils within the aneurysm as densely as possible to achieve complete angiographic occlusion, or until another coil could no longer be inserted. After the procedure, a three-dimensional (3D) angiography was obtained to assess the result.
For patients treated with stent-assisted coiling, the patients with unruptured aneurysms were given a dose of 100 mg of clopidogrel and 75 mg of aspirin orally for at least 3 days. For patients harbouring a ruptured aneurysm, a loading dose of 300 mg of aspirin and 225 mg of clopidogrel was given at least 4 hours before the procedure. After the procedure, the patients were maintained on daily clopidogrel (75 mg) and aspirin (100 mg) for 6 weeks, followed by aspirin alone (100 mg daily) for another 6 months. Intraperative heparinization was achieved by adding 3000 IU of heparin to 500 mL of 0.9% w/v sodium chloride infusion solution, which was administered through the guiding catheter during the procedure.,
Follow-up DSA re-examination was performed at a mean interval of 9.2 ± 5.1 months (range 6–33 months) after the primary procedure. Postoperative angiographic occlusion rate, technical success, follow-up images, and complications were independently evaluated by two interventional neuroradiologists (M. Lv and Y. Li). Evaluation of the outcome status was according to the modified Rankin Scale (mRS) as follows: 0, no symptoms at all; 1, no significant disability; 2, slight disability; 3, moderate disability; 4, moderately severe disability; 5, severe disability; and 6, dead.
Quantitative data were expressed as mean ± standard deviation. The statistical significance between patients having the ruptured and unruptured aneurysms was assessed by the Fisher's exact test, chi-square test, or two-sampled t-test. The pre- and post-treatment mRS scores were tested with the paired-sample test. A P < 0.05 was considered statistically significant.
Angiographic features in both the groups having a ruptured or an unruptured aneurysm are shown in [Table 1]. The depth-to-neck ratio of the ruptured group was similar to that of the unruptured group (1.5 ± 0.5 vs. 1.4 ± 0.3, P = 0.543). The maximum diameter of aneurysms in the ruptured group was significantly smaller than that in the unruptured group (3.6 ± 1 vs. 6.1 ± 4.4 mm, P = 0.029). The mean neck size in the ruptured group was also smaller than that in the unruptured group (2.6 ± 0.8 vs. 4.3 ± 2.4 mm, P = 0.010).
Among the 38 patients, 12 patients (31.6%) had accompanying cerebral anomalies. Ten patients (26.3%) had multiple intracranial aneurysms, one had a cerebral arteriovenous malformation, and one had a dural arteriovenous fistula. Twenty one (55.3%) aneurysms were on the right side and 17 (44.7%) on the left side. Saccular aneurysms were found in 34 patients and dissecting aneurysms in 4 patients.
Twenty-two aneurysms (57.9%) were at the proximal one-third of the A1 segment, seven at the middle one-third (18.4%), and 9 at the distal one-third (23.7%).
The 3D angiography revealed that 23 aneurysms had a superior direction; 10, an inferior direction; 4, an anterior direction; and 1, a posterior direction. Thirty aneurysms (78.9%) were unrelated to perforators on DSA. In eight patients (21.1%), perforators were found at the neck of the aneurysms.
Among the four dissecting aneurysms, two rose from the proximal and middle one-third of the A1 segment, one from the middle one-third, and one from the distal one-third.
16 patients were treated with a steam-shaped S-curve, 16 with a preshaped 45°-curve, and 6 with a steam-shaped C-curve microcatheter.
Among the 38 patients, 24 (saccular 24, dissecting 0) aneurysms were treated utilizing the single-catheter technique; 8 (saccular 7, dissecting 1) aneurysms with the stent-assisted coiling (Enterprise 3, Solitaire 5) [Figure 2]; 5 (saccular 2, dissecting 3) aneurysms with parent vessel obliteration; and, 1 (saccular 1, dissecting 0) aneurysm with balloon-assisted coiling. The immediate results of coil embolization revealed complete occlusion in 21 aneurysms (55.3%), near-complete occlusion in 16 (42.1%) aneurysms, and partial occlusion with the contrast agent filling in the aneurysm sac in 1 (2.6%) aneurysm. In eight aneurysms involving the perforators, the perforator branches were angiographically preserved during the procedure.
With regard to the 10 patients with multiple aneurysms, 2 patients in the ruptured group and 6 patients in the unruptured group underwent a single-staged coiling. The other two patients in the the ruptured group were treated with staged coiling.
The dural arteriovenous fistula was conservatively treated by keeping the patient on a regular follow up. The cerebral arteriovenous malformation (AVM) in one patient was treated with Onyx embolization, and partial occlusion of the AVM was achieved.
Major complications such as aneurysmal perforation, thromboembolic events, or coil protrusion related to stent-assisted embolization were encountered in 6 (15.8%) of the 38 patients [Table 2]. The complication rate in the ruptured group was not significantly higher than that in the unruptured group (P = 0.194).
Aneurysmal perforation was observed in four patients, and all patients recovered well after immediate coiling. Coil protrusion into the parent vessel occurred in one patient, which caused the occlusion of the A1 segment, but the patient suffered no symptoms owing to the supply from the contralateral ICA via the AComA. Coil protrusion into the distal branch of the middle cerebral artery was found in one patient, and the coil was salvaged by a 4-mm × 15-mm solitaire stent; the patient suffered no symptoms.
Follow-up DSA evaluation after coil embolization was performed in 32 aneurysms (mean interval 22.6 ± 6.7 months; range 10–37 months). The follow-up obliteration rate was 84.2% (32/38). The final follow-up DSA results showed that 31 patients (96.9%) remained stable and without regrowth of the aneurysm, while minor recanalization was found in 1 patient (3.1%). In the latter patient, the residual aneurysm sac was completely re-embolized.
Pre- and postembolization clinical scores
The pre-embolization mRS score was 0–1 in 32 patients, 2–3 in 5 patients, and 5 in 1 patient. Although successful coiling embolization was performed, one patient with Hunt and Hess grade IV died during the in-hospital period owing to the complications associated with SAH. Clinical follow-up was obtained in 37 of the 38 patients, with a mean duration of follow up of 26.6 ± 7.7 months (range, 18–44 months; mRS scores 0 in 34 and 1 in 3). The improvement seen following treatment in the mRS scores (P < 0.001) was statistically significant (excluding the case with complications related to SAH, who expired).
To our knowledge, only a few centers have reported a series of more than 10 cases of A1 aneurysms; most of the studies have a small number of recruited patients., 5, ,, In our series, A1 aneurysms comprised 1.7% of all patients with aneurysms. Moreover, most of the A1 aneurysms in our series were saccular aneurysms, and only four cases were dissecting aneurysms. Dissecting aneurysms are usually found in the intracranial portion of the carotid or vertebrobasilar circulation, and A1 segment of the ACA is especially a rare location., In 1992, Suzuki et al., retrospectively reported a large series of 38 A1 aneurysms treated by surgical clipping. Among the 38 aneurysms, 37 aneurysms were saccular and one was fusiform. The outcomes after surgical clipping at discharge from the hospital revealed that 28 cases were in an excellent neurological status, 6 cases had a good neurological status, and in 1 case, the neurological status was fair; 3 patients died owing to vasospasm in 2 cases, and an inadequate clipping of a basilar tip aneurysm in 1. In 2014, Cho et al., reported the largest series of 48 patients with 50 A1 aneurysms treated by an endovascular approach, and 39 aneurysms (78%) involved the proximal one-third of the A1 segment. Successful aneurysmal occlusion was achieved in 76% of the patients, and no procedure-related morbidity and mortality was detected.
Although large or giant aneurysms of the A1 segment have been reported in the literature,,, it is noticed that A1 segment aneurysms usually have a smaller size and that aneurysms at this location are usually prone to rupture even when they have a smaller size.,,, In 2010, Lee et al., reported 18 ruptured A1 aneurysms, and found that the average size was 6.95 mm. In 2015, Maiti et al., reported a group of 16 patients with A1 aneurysms, and found that the mean size in the ruptured group was significantly smaller than that in the unruptured group (4.38 vs. 6.23 mm). Hence, the author suggested that A1 aneurysms should be treated promptly to prevent adverse consequences in the future, even if they are small. In addition, Wakabayashi et al., reported an average diameter in eight ruptured A1 aneurysms of only 3.6 mm.
Another phenomenon that needs to be noted is that A1 aneurysms are usually associated with vascular anomalies (25–87.5%)., 5, ,, In our series, 12 (31.6%) patients had accompanying vascular anomalies. In addition, A1 segment aneurysms commonly involve perforators or branch vessels, such as the recurrent artery of Heubner (RAH), yet these branches are usually not evident on conventional angiography. The recent anatomic study by Avci et al., on 62 hemispheres showed that most of the RAHs arose from the A2 segment (63.6%), followed by the communicating segment (28.5%), and rarely from the A1 segment (7.8%). Lubicz et al., reported similar findings that 2 (25%) of 8 A1 segment aneurysms did not involve perforators. In our study, based on the 3D DSA imaging, most aneurysms had an inferior or superior direction, and only eight cases (21.1%) were related to perforators.
While considering treatment of A1 aneurysms, surgical clipping has been regarded as the first priority in earlier reports.,,,,, Hino et al., reported that separating the perforating arteries from the neck or the dome of the A1 aneurysm and preserving the vessel, present a substantial challenge to the surgeon, as the aneurysm is almost always behind the parent artery in the surgical field, making it difficult to gain good access to this particular type of aneurysm. To our knowledge, only four reports of endovascular management of A1 segment aneurysms have been published.,,, In some cases, the selective endovascular treatment of wide-neck aneurysms can be challenging and may require adjunct techniques. The use of stent has resulted in excellent occlusion rates for these aneurysms and has decreased the rates of angiographic recurrence. In this study, the follow-up angiographic results showed that 96.9% of the aneurysms remained stable without aneurysmal recurrence. In 2010, we reported our experience with endovascular treatment of cerebral aneurysms with the use of stents (Neuroform, Leo, and Wingspan stents) in small cerebral vessels, which included four cases with an aneurysm in the A1 segment. In that study, no immediate or delayed device-related complications were observed.
In our study, we performed the parent vessel occlusion in five patients. During the procedure of parent vessel occlusion, it would be difficult to salvage all perforators owing to the long segmental involvement of the fusiform aneurysm. The patients, however, showed an excellent clinical outcome with no added neurological deficits and the perforators being spared. Before parent vessel occlusion, a detailed evaluation of the perforators and the collaterals from the contralateral circulation is imperative. Angiographic demonstration of filling of bilateral A1 segments and a patent AComA from the contralateral ICA should be demonstrable using manual compression of the ipsilateral ICA (Mata test) or the ipsilateral ICA balloon-test occlusion., Tollard et al., evaluated the feasibility and efficacy of A1 occlusion in nine patients and suggested that parent artery occlusion was effective in treating wide-necked aneurysms arising from the A1 segment in patients with an adequate supply (bilateral A1 segments and a patent AcomA) from the contralateral ICA and A1 segments. Our series showed that most of the A1 aneurysms usually arise at the origin of a minor perforating artery and not at the origin of the cortical branches or the RAH. To limit the risk of perforator infarction, it may be safer to carefully look for the RAH and to limit the length of the coil occlusion to the parent vessel. Recently, the pipeline embolization device (PED) has been recommended as a beneficial technique for dissecting aneurysms. In 2015, Maiti et al., applied the PED to two dissecting aneurysms and achieved reliable outcomes. However, placement of the PED may result in infarction due to the occlusion of the perforators. Hence, the PED may be the ideal device for A1 aneurysms without any apparent perforators or side branches.
In our study, the overall complication rate was 15.8%, which is similar to that published in the previous reports (16.7%, 1/6). Tollard et al., reported nine cases of A1 aneurysms treated by the parent vessel occlusion; right hemiparesthesia was found in one patient, and the complication rate was 11.1%. In 2011, Chang et al., reported 12 cases treated by the endovascular approach; 3 patients (25%) had procedural complications. Recently, Cho et al., reported 48 patients harboring 50 A1 segment aneurysms; 7 patients (14.6%) suffered procedural complications (thrombosis in 6 patients and aneurysmal perforation in 1 patient).
Endovascular treatment is feasible and effective for A1 segment aneurysms. The current treatment selections, including the single-catheter embolization, balloon-assisted coiling, stent-assisted coiling, or parent vessel occlusion, should be chosen according to the characteristics and morphology of A1 aneurysms.
Financial support and sponsorship
The Commission of Beijing Municipal Science and Technology, municipal clinical special application study, special fund project (No. Z14110000211441); Beijing Talents Training Project (Category D); Beijing Hygiene System High-level Hygienic Technical Personnel Training Program; and, the Talents Program of Beijing Tiantan Hospital (Hospital Backbone Program).
Conflicts of interest
There are no conflicts of interest.
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