Neurol India Home 

Year : 2010  |  Volume : 58  |  Issue : 4  |  Page : 576--580

Endovascular embolization of very small cerebral aneurysms

Peizhuo Zang, Chuansheng Liang, Qiang Shi 
 Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, China

Correspondence Address:
Peizhuo Zang
Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Heping Beier Street, 110001, Shenyang


Background : Very small cerebral aneurysms are considered to be one of the challenges for endovascular treatment, with difficulty for catheterization and high risk for intraoperative rupture. We report the treatment of very small (< 3-mm) cerebral aneurysms by coil embolization. Materials and Methods : We performed a retrospective analysis of 11 consecutive patients with very small aneurysms treated by coil embolization in our institute between February 2007 and February 2009. Results : Three-dimensional rotational angiography (3DRA) was most accurate in the detection of these aneurysms; 3DRA revealed the aneurysms in two patients in whom conventional angiography failed to demonstrate the aneurysms. The Hunt-Hess (HH) grade was grade 0 (unruptured aneurysm) in one patient and grade I in ten patients. Coil embolization was successfully performed in 11 patients. Complete (n = 8) or near complete (n = 3) immediate occlusion was obtained. One or three soft coils were used in all the patients with the shortest available length. Balloon assistance was used in one patient and stent assistance was used in seven patients. Although coil migration into the MCA was seen in one patient and intraoperative aneurismal rupture occurred in one patient, no untoward clinical complication was seen. Follow-up DSA in 11 patients demonstrated persistent occlusion (n = 9) or progressive thrombosis (n = 2) of the aneurysms. All the patients with available follow-up had a modified Rankin Score (mRS) of 0. Conclusion : HH grade 0 and I very small cerebral aneurysms can be treated by endovascular coil embolization. Use of short, soft coils and balloon/stent assistance is useful.

How to cite this article:
Zang P, Liang C, Shi Q. Endovascular embolization of very small cerebral aneurysms.Neurol India 2010;58:576-580

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Zang P, Liang C, Shi Q. Endovascular embolization of very small cerebral aneurysms. Neurol India [serial online] 2010 [cited 2020 Sep 24 ];58:576-580
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The International Subarachnoid Aneurysm Trial (ISAT) documented the superiority of endovascular treatment of ruptured aneurysms over clipping, when both the treatments were considered feasible. [1] However, there are challenges for endovascular treatment, one of which is the very small size (<3 mm) of the aneurysm. Endovascular treatment of these aneurysms is considered to be technically challenging, and high complication rates have been reported. [2],[3],[4] Very few series have focus on the outcome of embolization of very small aneurysms. Suzuki et al. [5] reported on the endovascular treatment of aneurysms less than 3 mm in diameter, with a favorable neck-to-fundus ratio. Gupta et al. [6] included cases with an unfavorable neck-to-fundus ratio treated with balloon assistance. There are few reports detailing the use of stents in very small aneurysms. We report our experience of endovascular treatment in this subset of very small aneurysms.

 Materials and Methods

We retrospectively reviewed 1102 patients with cerebral aneurysms treated by endovascular method in our center between February 2007 and February 2009. In this study aneurysms measuring less than 3 mm in diameter were included. Aneurysms with an unfavorable neck-to-fundus ratio were also included in the study. Eleven patients (1%) fulfilled the inclusion criteria [Table 1]. There was female gender predominance, 10 women with age ranging from 25 to 55 years (mean age 38.3 years). The locations of the aneurysms were P1 of the posterior cerebral artery (n = 2), A1 of the anterior cerebral artery (n = 2), ophthalmic segment of the internal carotid artery (n = 5), posterior communicating artery (n = 1), and vertebral artery (n = 1). Subarchnoid hemorrhag (SAH) was documented by computerized tomography (CT) scan in ten patients. The Hunt-Hess (HH) grade was grade 0 in one patient and grade I in ten patients. Five patients were treated within three weeks of SAH. Six patients were referred to our hospital for treatment more than a month after the bleed.{Table 1}

The embolization procedure was performed with the patient under general anesthesia. Digital substraction angiography (DSA) was performed followed by three-dimensional rotational angiography (3DRA). The results on DSA were negative in two patients in whom the aneurysms were detected by 3DRA. Guided by the 3D images, we obtained additional DSA images to evaluate the morphologic features of the aneurysm. Measurement of the aneurysmal size was made on the 3D angiograms. Under roadmap guidance, a microcatheter (SL-10; Boston Scientific, Natick, MA, USA/Echelon-10, M.T.I-ev3, CA) was carefully guided over a microguide wire (Agility-10; Cordis, Miami Lakes, FL, USA; Synchro-14, Boston Scientific) into the aneurysm. A wire was never introduced into the aneurysm, and the catheter was shaped so that it pointed toward the aneurysm. The tip of the catheter was kept at the neck of the aneurysm, and, if needed, the catheter was navigated farther into the aneurysm over the first coil loop. Another angiogram was performed at this stage to evaluate aneurysmal opacification. Balloon assistance was used in one case and stent assistance was used in seven patients (five Neuroform stents; Boston Scientific, Natick, MA and two Leo stents; Balt, Montmorency, France) as a salvage option after balloon assistance failed. The shortest available length of a soft coil was used. The coil placement was done very slowly, and subtle microcatheter manipulation was used to avoid tension build-up in the aneurysm and to allow the coil loop to form inside the aneurysm. If balloon assistance was used, the balloon inflation was varied during coil placement to allow for microcatheter movement. If stent assistance was used, the microcatheter, used for coil delivery, was initially probed of the aneurysm, followed by stent deployment. Also, the patient was premedicated with aspirin 300 mg and clopidogrel 325 mg by mouth, 2 hours before the use of stent. High magnification was useful to observe the coil movement inside the aneurysm. At the end of coil placement, the microcatheter was slowly withdrawn so as to give the coil enough space in the aneurysm. If the tip of the coil was seen projecting outside the aneurysm, further manipulation was not attempted. Even if minimal contrast filling was seen, no additional coil placement was attempted. Low-molecular-weight heparin was given for 24 hours.


Coil placement was successful in 11 patients. Complete immediate aneurysmal occlusion was seen in eight patients, with minimal residual filling in three patients. The residual filling, if seen, was seen in the center of the 2-mm coil loop. In one patient one 2 mm Χ 1 cm coil migrated into the MCA after detachment and the cortical was occluded on angiography. No untoward consequence of coil migration was seen in this case. In one patient, inraoperative aneurismal rupture was experienced during the first coil placement and the aneurysm was completely occluded with other two coils. The patient did not have any clinical sequelae. All the patients had unchanged clinical status after embolization. The follow-up ranged from 3 to 21 months, with a mean follow-up of 7.4 months. All the patients with available follow-up had a modified Rankin Score (mRS) of 0. Follow-up DSA in all the patients revealed complete occlusion of the aneurysm. Minimal aneurysmal filling seen in two of the patients had completely disappeared.

Illustrative cases

Case 1

A 46-year-old woman presented with SAH (HH grade I) of two days duration. DSA revealed a small bulge at the ophthalmic segment of the left internal carotid artery [Figure 1]a. The DSA in the anteroposterior projection revealed that the aneurysm had a narrow neck and measured 3 Χ 1.5 mm. Coil embolization was performed with a HyperSoft 2 mm Χ 1 cm coil (MicroPlex; Mi-croVention, Aliso Viejo, CA, USA) [Figure 1]b, resulting in an almost complete occlusion of the aneurysm [Figure 1]c. The patient made considerable recovery after treatment.{Figure 1}

Case 2

A 55-year-old woman presented with a 3-week-old SAH (HH grade I). 3DRA revealed a very small (2.6 Χ 2.2 mm) internal carotid artery (ICA) aneurysm with a broad neck [Figure 2]a. The neck-to-fundus measurement was 2 mm, and stent-assisted coil embolization was performed with four HyperSoft coils (3 mm Χ 4 cm, 2 mm Χ 2 cm, 2 mm Χ 2 cm, 2 mm Χ 1 cm, MicroPlex; Mi-croVention, Aliso Viejo, CA, USA), resulting in nearly complete occlusion of the aneurysm [Figure 2]b-d. No thrombus formation was seen, and the patient was extubated in intact neurologic condition. Low-molecular-weight heparin was given for 24 hours followed by aspirin (100 mg once a day) and clopidogrel (75 mg once a day) for 6 months. At 6-month follow-up, mRS was 0.{Figure 2}


As seen in our study, aneurysms smaller than 3 mm can also result in SAH and 3DRA was most appropriate in the detection, analysis, and planning for endovascular therapy. CTAand DSA may not detect some of these aneurysms. Lack of sensitivity and interobserver variation of CTA in the detection of very small aneurysms has been seen in previous studies. [7] This is related to the lower resolution of CTA compared with DSA. [8] 3DRA and DSA are of higher resolution than CTA and are better in the detection of aneurysms and in defining the morphologic features of the aneurysm [15] . The relationship with adjacent small vessels is also likely to be more accurately delineated by conventional angiography. Van Rooij et al. [9] have also reported that very small aneurysms can be commonly detected by 3DRA despite negative findings on DSA. These very small aneurysms can be interpreted as the loop of the vessel or can be overlapped by normal arteries in conventional DSA and 3DRA is useful in these circumstances. However, in some of the cases, the true aneurysm morphology, particularly the neck size, was clearly delineated by the DSA performed according to the angulations shown by the 3D images. The reason may be inadequate filling of the aneurysm or of higher resolution of conventional DSA compared with 3D imaging, which may be crucial in the assessment of very small aneurysms. Surgical treatment of very small aneurysms poses a unique challenge because they are often thin-walled and may be too small to accept a clip without narrowing or tearing the parent vessel. In such cases, wrapping of the artery with muscle, Surgicel (Ethicon, Somerville, NJ, USA), or muslin gauze, coating of the aneurysm with vinyl polymers or cyanoacrylate adhesives, and direct coagulation of the aneurysm have been variably described as treatment options. [10],[11],[12] In a similar fashion, very small aneurysm sizes may challenge endovascular options. [2] Small size makes for challenging aneurysm catheterization, unstabilitation of the microcatheter and the risk for perforation by microcatheters that load and spring forward, and difficulty placing multiple coils. [2],[11] The small size of the aneurysm may be associated with a higher risk for rupture during embolization. [3],[4] Review of the literature revealed only two studies by Suzuki

et al. [5] and Gupta et al., [6] in which endovascular treatment of very small aneurysms have been reported. However, Suzuki et al. [5] studied aneurysms of at least 3 mm with a favorable fundus-to-neck ratio of 1.5 and Gupta et al[6]. treated these very small aneurysms with unfavorable fundus-to-neck ration by balloon-assisted coiling. To this end, there are no reports in the literature detailing the feasibility, use, or safety of stents in small (<3 mm) cerebral aneurysms. The confirmation of endovascular therapy has stimulated an increase in research in this field, allowing rapid development of new tools such as the Neuroform stent. Nowadays, the LEO and Wingspan stents are also available in China. [13] The release of newer sophisticated devices, such as high-density mesh intracranial stents like Silk (BALT, France) and Pipeline (M.T.I-EV3, USA) enables treatment of lesions that were previously deemed unclippable and uncoilable small aneurysms. This article describes seven patients who have safely and successfully undergone stent treatment in very small aneurysms with positive results. Although one 2 mm Χ 1 cm coil migrated into the MCA, no untoward consequence of coil migration was seen in this case. There was no intraprocedural thrombus formation. This outcome does reinforce the use of the stents for electively treated aneurysms. The development of sophisticated small adjunctive devices such as the stent increases the type and number of aneurysms that can be treated by endovascular means and with improved safety. High-grade patients usually require external ventricular drainage and the use of stents and the obligatory use of dual antiplatelet agents is warranted, so we give endovascular approaches to HH grade 0 and I cases.

A major limitation of the endovascular treatment of small aneurysms was the possibility of intraoperative rupture. Nguyen et al. [3] reported a fivefold increase in the incidence of rupture during endovascular treatment of aneurysms that were <3 mm compared with larger aneurysms. To prevent this complication, careful microcatheter placement at the neck of the aneurysm and use of the soft coil loop to enter the aneurysm were useful. The coil chosen was of shortest length of soft type to avoid excessive manipulation and tension build-up in the aneurysm. In fact, even if the coil tip was seen to protrude in the parent vessel, it was considered to be acceptable; therefore, forceful or repeated manipulations were avoided.

Use of balloon in these cases is extremely useful, not only for treating wide neck aneurysms but also for treating those with favorable neck. Even if it is not used for remodeling, the balloon should be in a position to be inflated in case of rupture. Nguyen et al. [3] also observed that among cases with procedure-related rupture, inflation of a compliant balloon was associated with better outcome. However, manipulation of the balloon had to be done with care so as to prevent sudden movement of the microcatheter tip. The balloon inflation was partial and varied during the coil placement so as to allow for microcatheter movement, except when the coil tip or loop tended to prolapse out of the aneurysm. Lim et al. [14] have studied the structural limitations of currently available microcatheters and coils for endovascular coiling of very small aneurysms. They observed that the lengths of the detachment zone, which is known to be a stiff segment, of the currently available coils were approximately 0.5-0.8 mm, and the distance between the distal end of the distal markers of the microcatheters and the detachment zone of the coil ranges from approximately 1.2 to 2.8 mm. Therefore, to prevent rupture of very small aneurysms during coiling, the distal marker of the selected microcatheter preferably should be located near the aneurysmal neck. At the end of coil placement, slow withdrawal of the microcatheter can help in avoiding any potential injury from the relatively stiff detachment zone. Refinement of currently available devices may be essential to achieve safer coiling of very small aneurysms.

Another issue is retention of the coils in such small aneurysms. Balloon assistance was of considerable help, particularly when the aneurismal neck was more than 2 mm so as to retain the coil loop inside the aneurysm. Goddard et al. [11] also reported on the use of a single coil in the treatment of small aneurysms with reasonable long-term stability in their series. In general, the mean age of 38.3 years in our series was lower than most series of aneurysms. This may have biased the results in favor of a positive outcome because anatomic features such as atherosclerosis or extreme tortuosity were absent in the younger age group, favoring precise catheter manipulation. The difficulty of the cases and the chance of complication or rupture are probably much higher in patients who are older and harbor these comorbidities. In view of technical issues in endovascular treatment, aside from the aneurysms at posterior circulation, it is important to note that the remaining aneurysms were surgically accessible and reasonable clipping options. We are concerned with the application of these methods in less than compelling circumstances may ultimately do patients a dsservice.

Very small (less than 3 mm) cerebral aneurysms in HH grade 0 and I cases can be treated by endovascular coil embolization. Use of short, soft coils and balloon/stent assistance is advantageous.


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