Complex intracerebral aneurysms (CIAs) are irregular, large or giant, wide-necked or combined with arterial branches, perforating vessels, atheromatous vessels, and partially thrombosed (1–3). The acutely ruptured complex intracerebral aneurysms (ARCIAs) result in devasting consequences, and the treatment of patients with ARCIAs has been cited as the most vexing scientific issue confronting neurosurgeons and neuroradiologists. Endovascular treatment of CIAs has become an effective alternative to standard surgical clipping (4–7). Despite the advances in endovascular technologies, the treatment of ARCIAs is considered more challenging due to the difficulties in positioning the microcatheter, the coil matrix's lack of support, the increased risk of parent vessel compromise, and the inability to pack the aneurysm densely compared with classic aneurysms with narrow necks (1, 3, 5).

Emerging data suggest that coil embolization may result in 50% to 60% recanalization rates in CIAs (8, 9). In endovascular coil embolization of ARCIAs, dense coil packing of the aneurysm sac is crucial in preventing recurrence (10, 11). To achieve the densest possible coil packing, it is essential to correctly select the appropriate embolization strategy. A growing body of literature reports using multi-microcatheter, stent coiling, microcatheter shaping, and balloon assistance for intracerebral aneurysms (IAs) embolization with good clinical follow-up results (12–15). Recent retrospective studies have reported that the dual microcatheter technique is a safe and effective treatment for acutely ruptured aneurysms due to low treatment-related complications and mortality (16–18). Although these studies are informative, most of these studies focus on describing the results of the studies and do not specifically address the selection of microcatheters for IAs embolization and the rationale for the selections. In addition, prior literature demonstrated the use of microcatheters to temporarily alter the configuration of the aneurysm neck and bifurcation branches (also known as microcatheter protection techniques) to assist in aneurysm embolization, rather than direct embolization of the aneurysm using microcatheter coil delivery (15, 19).

Herein, we presented our initial experience with a microcatheter-guided compartment packing (MCP) technique for ARCIAs. The MCP technique was that the distal tips of the microcatheter were cast into different shapes based on the aneurysm type, shape, and dome orientation, and the tips of microcatheters were placed in a different compartment within the aneurysm to deploy the coils simultaneously or sequentially. The intraoperative microcatheter was adjusted according to the embolization strategy, and the microcatheters might be adjusted according to the embolization area of the expected aneurysm, even with the single microcatheter technique. Additionally, more 3-dimensional (3-D) coils were used intraoperatively to be woven into a basket based on preset microcatheter varying with the size and shape of the aneurysm since coil selection is an essential factor in successful embolization and postoperative recurrence (16). The MCP technique enables neurointerventionalists to effectively lock the coil to form a stable frame, reduce the likelihood of coil protrusion, and achieve a high-volume embolization ratio for ARCIAs.

Twenty-eight patients presenting with subarachnoid hemorrhage (SAH) secondary to ruptured complex intracerebral aneurysms (RCIAs) were enrolled in treatment with the MCP technique based on the inclusion criteria between January 2021 and January 2022. Patient demographics and aneurysm characteristics are summarized in Table 1. This study included 28 patients (20 women and 8 men) aged from 29 to 79 years, with a mean age of 55.96. Five (17.9%) patients were in severe clinical condition (Hunt-Hess grade 4–5), and five (17.9%) patients had severe aSAH (mFisher grade 3–4) on admission. The aneurysms had sizes ranging from 2.80 to 19.87 mm (mean 7.53 mm), necks of 4.10 to 10.50 mm (mean 5.96 mm), and dome-to-neck ratios of 0.51 to 4.01 (mean 1.29). Twenty-one (75.0%) aneurysms presented irregular shapes. Sixteen (64.3%) aneurysms were located in the anterior circulation, and the other 10 (35.7%) were in the posterior circulation. Pre-treatment mRS score was 0.

Endovascular embolization of ARCIAs using the MCP technique showed technical success in all patients. Seventeen (60.7%) aneurysms were treated with the double-microcatheter MCP technique, and 11 (39.1%) were treated with the single-microcatheter MCP technique (Table 2). Thirteen (46.4%) aneurysms were treated with coil only, and 15 (53.6%) aneurysms received stent-assisted coiling. Of 28 patients treated with the MCP technique, 24 (85.7%) aneurysms were considered complete occlusion (Raymond I) based on the immediate postembolization angiogram results (Table 2). In contrast, four (14.3%) aneurysms were considered Raymond II. Figures 2–5 illustrate anterior communicating artery (AComA), middle cerebral artery (MCA), posterior communicating artery (PcomA), and anterior inferior cerebellar artery (AICA) aneurysms embolization process.

Complications occurred in 2/28 treatments, including guidewire perforation with SAH (directly related to the procedure) and cerebral vasospasm-related cerebral infarction. Aneurysm perforation occurred due to trauma caused by the pushing guide wire of a small daughter sac located above the treated aneurysm. As a result, the patient developed a small SAH. Postoperatively, the patient presented with headache symptoms, which almost wholly subsided after treatment, and the mRS score at discharge was 0. The DSA or MRA follow-up at 6 months post-embolization was available for all 28 survivors, demonstrating complete occlusion in 25/28 (89.3%) aneurysms, and the recanalization rate was 3.57% (Table 3). Twenty-six (92.9%) patients had a favorable 90-day outcome (mRS 0–2) after the endovascular coil embolization.

ARCIAs have always been a tremendous challenge for surgical clipping and endovascular coiling due to their complex vascular anatomy. In clinical practice, we introduced an MCP technique for ARCIAs and applied it to aneurysm embolization. Here, we listed four clinical applications of the MCP technique for ARCIAs embolization (Figures 2–5). The principal findings obtained in the present study are as follows. Of 28 patients successfully treated with the MCP technique, 24 (85.7%) aneurysms were considered as complete occlusions, and an angiography follow-up at 6 months post-embolization demonstrated complete occlusion in 25/28 aneurysms. The rate of recanalization at 6 months post-embolization was 3.57%. Moreover, we proposed a hypothetical model diagram in Figure 6 to embolize an aneurysm using the MCP technique, where the microcatheters were placed in a different compartment within the aneurysm to deploy the coils simultaneously or sequentially. Our report presents initial clinical experiences with the MCP technique, which provides a safe, reliable, and practical approach to the endovascular embolization of ARCIAs.

Several pieces of literature have demonstrated the use of microcatheters to temporarily alter the configuration of the aneurysm neck and bifurcation branches (also known as microcatheter protection techniques) to assist in aneurysm embolization (15, 16, 19). The present study differs from the previous literature in several ways. First, the MCP technique used in our case series was used to deliver coils. Second, our case series illustrated that the intraoperative microcatheter is adjusted according to the embolization strategy, and the microcatheter can be adjusted according to the embolization area of the expected aneurysm, even with the single microcatheter technique. Third, more 3-dimensional (3-D) coils were used intraoperatively to be woven into a basket based on a preset microcatheter varying with the size and shape of the aneurysm in our case series. Finally, coil-assisted embolization can be used for aneurysms with multiple daughter sacs and wide necks. The rims in the second partition must climb several times within the first partition to increase the stability of the rims in the second partition.

Compared with surgical clipping, endovascular treatment has become a preferred method in most cases for treating unruptured and ruptured IAs—over 50% of IAs are treated via endovascular coiling (7, 29, 30). Difficulties in traversing the microcatheter through tortuous vasculature, guiding the microcatheter tip to the 1/2 or 2/3 position within the aneurysm, and maintaining it in a stable position account for many coil embolization procedures fail. These causes include incomplete aneurysm occlusion (16, 31, 32), aneurysm recanalization (31), coil misalignment (33), and intraoperative rupture (34). These failures can be attributed to unfavorable vessel tortuosity and CIAs geometry. CIAs of varying shapes and sizes, and the stability of the intra-aneurysm embolization coil after intervention remain challenges for endovascular embolization techniques (7). Based on the MCP technique, the neurointerventionalist may advance the coil filling at the working projection without hesitation and may not worry about moving the microcatheter into the parent vessel or filling the coil into the parent vessel.

The MCP technique has several unique strengths. First, it exploits the superior tracking capabilities of the microcatheter, allowing flexible and maneuverable embolization of aneurysms in tortuous vasculature or smaller distal arteries. This technique can avoid remodeling and repositioning the microcatheter later and reduce surgical time and postoperative complications. Second, the MCP technique facilitates intraoperative selection of coil size. In the compartments of the aneurysm, the coils are gradually and orderly piled up, stabilizing the coils, and making them less likely to come out of the vessel. On the other hand, the microcatheter is simultaneously placed in the aneurysm sac, keeping the coils in place, and intertwined to reduce the chance of protruding. Third, the MCP technique facilitates dense embolization. It allows placing many coils in the aneurysm sac, creating a stable build before separating them. During the procedure, the distal tips of the microcatheter are steam-shaped in different shapes according to the shape of IA, and the tips of the microcatheters are implanted in different parts of IAs. ARCIAs are then densely embolized by using the microcatheters simultaneously or alternately. It should be noted that when stent-assisted embolization is used, anti-platelet aggregation drugs such as tirofiban must be used. At this time, forming an intratumoral thrombus in the aneurysm is complex, and ARCIAs can achieve the purpose of dense embolization of the aneurysm with the MCP technique. On the other hand, if stent-assisted embolization is necessary, using the MCP technique can effectively reduce coils escaping from the aneurysm cavity, increase coil packing density, and reduce aneurysm recurrence. In a literature review of stent-assisted coil embolization for ARCIAs, 63% of aneurysms exhibited complete occlusion (35). A published series with a large population using stent-assisted coil embolization for ARCIAs showed immediate occlusion in 87.5% of patients (36–39). From a multitude of perspectives, when coils are loosely packed on ruptured aneurysms, they appear to increase the risk of recurrent SAH, re-ruptured, and postoperative recurrence (15, 16). In the present study, satisfactory aneurysm occlusion was achieved in 89.3% of cases at 6 months postembolization, and the recanalization rate of 3.57% was low. The MCP technique can effectively increase the coil packing density, reduce perioperative re-rupture or rebleeding, and minimize the risk of postoperative recurrence.

The MCP treatment for ARCIAs is a double-edged sword, raising three serious concerns. First, placing two or more microcatheters into the aneurysm may increase the risk of rupture. In this study, a guidewire-induced aneurysm perforation occurred, resulting in SAH. The previous literature reported that the incidence of rebleeding caused by two or more microcatheters was 3% (14, 15), which is similar to the 2.0% to 7.3% reported incidence for all aneurysms regardless of size or presence of subarachnoid hemorrhage (14, 31). Second, coiling ARCIAs without a stent or balloon may increase the risk of coil protrusion and parent artery occlusion (36–40). Although no similar complication occurred in our cases, it still requires concern. Third, coiling ARCIAs without stent or balloon assistance may reduce packing density and increase recurrence rates (36, 38–41). In our case, complete occlusion (Raymond I) was achieved in 89.3% of cases at 6 months postembolization, and we look forward to long-term follow-up results. Taken together, neurointerventionalists need to carefully balance the risk of aneurysm recurrence with the inherent risk of stent or balloon remodeling. Nevertheless, it is undeniable that stent-assisted coil embolization has been increasing for ARCIAs (25, 42).

Notably, not all ARCIAs can be treated endovascularly. Up to 25% of surgical neurointerventions fail in attempted endovascular treatment of intracranial aneurysms (7). Some ARCIAs require revascularization techniques, including extracranial-to-intracranial carotid artery bypass with aneurysm clipping or distal or proximal arterial occlusion, intracranial-to-intracranial bypass, and excision of the diseased segment with direct vessel revascularization (in situ bypass) (1, 43). Future studies are needed to explore whether the MCP technique can guide the choice of surgical modalities for the revascularization of such CIAs. Moreover, we did not obtain a long-term follow-up result in our patients even though we obtained a good packing density and stable short-term outcome. Further follow-up and application in more patients will be required. Third, since the sample size in the present study was small, larger-scale clinical trials are needed to verify the generalizability of the present findings. Fourth, for treating giant aneurysms, the use of MCP technology requires the use of bilateral femoral artery sheath and multi-catheter system technology, which may increase surgical complexity, heighten the risk of intraoperative complications, and increase operative times.

The MCP technique is simple, safe, and effective, achieving good packing density and initial occlusion rate when used for the treatment of ARCIAs, and may serve as an option for treating ARCIAs. Further studies are necessary to evaluate its long-term effectiveness.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

The studies involving human participants were reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Fujian Medical University. The Ethics Committee waived the requirement of written informed consent for participation.

Y-BZ, D-ZK, and S-FZ designed the study. Y-BZ, B-SX, H-JW, and S-XH collected, analyzed data, and drafted the manuscript. W-JF, MZ, G-RC, P-SY, L-SD, and L-HY helped with the figures and result in interpretation. D-LW, L-SD, L-HY, D-ZK, and S-FZ reviewed and revised the manuscript. L-SD, D-ZK, and S-FZ were identified as the guarantor of the article, taking responsibility for the integrity of the work as a whole. All authors contributed to the article and approved the submitted version.

The study was supported by the National Natural Science Foundation of China (Nos. 81870930 and 82171327) and Qihang Fund Project of Fujian Medical University (2019QH1262).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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