Introduction

The surgical clipping of posterior circulation aneurysms poses a great technical challenge to the practicing neurosurgeon.5)17) Since microsurgical clipping involving the posterior circulation aneurysms is associated with several problems, including the narrow and deep operation field, and complex anatomical structures, it may cause severe postoperative neurological deficits.2)6)17) However, endovascular treatment (EVT) of intracranial aneurysms has made remarkable progress over the last decade with development of technology and device, such as selfexpandable stent and remodeling balloon.1)3)4)8)10)11)19)20)

Furthermore, recently published results of the International Subarachnoid Aneurysm Trial (ISAT)14) and other study21) have done much to make aneurysm coiling acceptable. Consequently, EVT has become accepted as an alternative to surgical clipping, with lower morbidity and mortality rates in some cases, particularly in posterior circulation aneurysms.10)13)18)22) However, even though EVT is an essential

modality for the treatment of patients harboring posterior circulation aneurysms, the main challenge continues to be the unacceptable rates of recurrence and the associated risks.4)7)17)18)23)

Therefore we consider that the appropriate selection of treatment modalities for posterior circulation aneurysms is important. The purpose of this study was to review the treatment outcomes and to emphasize the necessity of maintaining the surgical ability for posterior circulation aneurysms.

Materials and Methods

1. Patients

During the past 10 years, 34 of the 570 patients who were treated in our hospital for cerebral aneurysms were found to be harboring posterior circulation aneurysms. Of these patients, 27 patients had subarachnoid hemorrhage (SAH). From January 2004 to June 2008, 13 patients with a posterior circulation aneurysm were treated by endovascular coiling, and 7 of these patients had SAH. We conducted a

comparative study of the pre-and post-introduction of EVT in our hospital respectively. The definition of a preendovascular (pre-EVT) period is from January 1998 to December 2003. The 13 patients was treated in pre-EVT period. In these patients, the 3 patients with basilar tip aneurysm and 3 patients with superior cerebellar artery (SCA) aneurysm were treated by extended pterional approach. And 7 patients with posterior inferior cerebellar artery (PICA) aneurysm were treated by retrosigmoid suboccipital approach. The definition of a EVT period is from January 2004 to June 2008. And we treated 21 cases of posterior circulation aneurysms, using microsurgical clipping for 8 patients and EVT for 13 patients in the EVT period. In the 8 cases of microsurgical clipping, the patients with 2 basilar tip aneurysm and 1 patient with posterior cerebral artery aneurysm (PCA) and 1 patient with SCA aneurysm were treated by extended pterional approach. And 4 patients with PICA aneurysm were treated by retrosigmoid

suboccipital approach. In the EVT group, the 13 patients were treated by coil embolization. In these patients, 2 patients were treated by two microcatheter technique and 1 patient was treated by stent and balloon assisted technique. The patients in each group were analyzed using medical records, initial neuroimaging studies comprising computed tomography (CT) and 4-vessel angiography, outpatient

charts, and operation video records. Hunt-Hess grades (H-H grades) and Fisher grades were obtained for all patients preoperatively. Postoperative neurological state follow-ups for 6 months were classified using the modified Glasgow Outcome Scale (mGOS). The definition of a good outcome is mGOS I or

II. In addition, the number of postoperative hospital days, morbidity, and mortality were obtained for all patients. 2. Demographics and clinical characteristics The microsurgical clipping group, comprised 6 male and 15 female patients, ranging in age from 38 to 70 years (mean 53 years). Of these patients, 20 had SAH. In 9 (45.0%) of these 20 patients, the SAH was given an H-H grade of II ; in 9 (45.0%), a grade of III ; and in 2 (10.0%), a grade of IV. With respect to the Fisher grades, 1 (5.0%) of the 20 patients

was given a grade of II, 6 (30.0%) a grade of III, and 13 (65.0%) a grade of IV (Table 1). The EVT groups, comprised 7 male and 6 female patients, ranging in age from 39 to 66 years (mean 51.7 years). Of these patients, 7 had SAH. In 3 of the 7 patients with SAH, the SAH was given an H-H grade of II ; in 3, a grade of III ; and in 1, a grade of IV. With respect to the Fisher grade, 1 (14%) of the 7 patients was given a grade of I, 1 (14%) a grade of III, and 5 (72%) a grade of IV (Table 1). 3. Treatment of the posterior circulation aneurysms after introduction of the EVT in our hospital We performed microsurgical clipping for 8 patients after introduction of the EVT (Table 2). Of the 8 patients, we performed microsurgery on 5 cases, because EVT was not suitable for the their lesions. In one of these patients (case 8), angiography was performed and revealed a bi-lobulated aneurysm with a branch arising from a sac in the left PICA (Fig. 1. A, B, C). The aneurysm was obliterated using 2 clips and patency of the PICA was checked by transcranial Doppler sonography using the left suboccipital approach (Fig. 1. D, E, F). The patient tolerated the operation well and was discharged without obvious neurological deficit.

In the second patient (case 7), preoperative angiography revealed a right SCA aneurysm with a broad neck that had developed at an acute angle (Fig. 2. A, B). This lesion was not considered suitable for stent-assisted endovascular treatment because of the acute angle and SCA diameter was 1.6mm. Thus, microsurgical clipping was performed (Fig. 2. C). The patient complained of temporary mild postoperative

oculomotor palsy, which recovered completely during the outpatient follow-up period. And in 3 patients (case 1, 3, and 4) we performed microsurgical clipping for 2 right PICA and basilar tip aneurysms. These aneurysms had an inadequate dome to neck ratio and relative wide neck. In one of these patients

(case 4), the patient presented with a small aneurysm (2.1mm ~ 1.9 mm in dome to neck diameter). So EVT was not suitable for this lesion due to the risk of coil herniation and migration into the PCA.

In addition to the abovementioned 5 patients, in 2 patients (case 5, and 6) we performed microsurgical clipping for right PCA (Fig 3. A, B, C) and basilar tip aneurysms. We thought that both EVT and microsurgical clipping were suitable for these lesion without complication. And we performed

microsurgical clipping because these patients were of a young age and required mandatory long-term follow-up. The patients treated using the microsurgical clipping provided informed consent about 2 treatment modalities. We performed the EVT for 13 patients (Table 3). Although the patients (case C, D, F, and G) had an inadequate dome to neck ratio, they was treated using EVT successfully. But 2

patients (case B and M) presented with the complication and failure of complete occlusion. In one of these patients (case B), angiography was performed and revealed a small bi-lobulated aneurysm with a broad neck in the left PCA (Fig. 4. A, B). Coiling of the aneurysm was performed through the stent and

balloon assisted technique. And postoperative angiogram revealed the incomplete occlusion of aneurysm (Fig 4. C). In the second patient (case M), preoperative angiography (Fig 5. A) was performed and revealed a small aneurysm with a broad neck in the left PICA. Coiling of the aneurysm was performed through two catheter technique (B). But the patient’'s mentality was decreased to the stuporous mentality

at the postoperative 4 days. So the magnetic resonance imagings (C. D) was performed and revealed the cerebellar infarction and occlusion of the parent artery.

Results

From January 1998 to June 2008, we treated 34 cases of posterior circulation aneurysms, using microsurgical clipping for 21 patients and EVT for 13 patients. When

results for two treatment modalities were compared each other, the results for EVT were superior in terms of both outcome and shortening of the number of hospital days. Good outcomes were recorded 80.8% of cases in the microsurgical clipping group, whereas for the EVT group, 92.3% of cases had good outcomes. The mean number of the postoperative hospital days was 34.3 days (15 to 87 days) in

the microsurgical clipping group and 18.6 (5 to 40 days) in the EVT group. And we treated for 4 patient with fusiform and dissection aneurysms in the EVT group (Table 1). From January 2004 to June 2008, we treated 21 cases of posterior circulation aneurysms, using microsurgical clipping for 8 patients and EVT for 13 patients. When the results for this period were compared with the result for a group of 13 patients treated with microsurgical clipping only over the pre-EVT period, the results for EVT period were superior in terms of both outcome and shortening of the number of hospital days. Good outcomes were recorded 69.2% of cases in the pre-EVT period group, whereas for the EVT period group, 95.2% of cases had good outcomes. The mean number of postoperative hospital days was 38.6 days (21 to 87 days) in the pre-EVT period group and 22.1 days (5 to 54 days) in the EVT period group (Table 4).

Discussion

The goal of aneurysm treatment is complete, immediate, permanent, and safe occlusion of the dome and preservation of the parent artery.3)23)

Although surgical clipping is considered to be the standard aneurysm treatment, microsurgical clipping of posterior circulation aneurysms is associated with several problems, including the deep anatomical position, narrow operation field, contusion from brain retraction, and damage to the perforating artery.

Consequently, it may cause severe postoperative neurological deficits.2)6)12)17) In contrast, EVT is considered

the most effective method for the treatment of posterior circulation aneurysms.1)6)17)22) In our study, we achieved better results in terms of mGOS and the number of postoperative hospital days through the EVT, compared to microsurgical clipping. And the cases for EVT was more than those of microsurgical clipping after introduction of the EVT. Furthermore, we treated for the other type of aneurysms,

such as fusiform and dissecting aneurysms. Jung et al.6)  reported that EVT is considered to be useful alternative treatment compared with surgical neck clipping, although long-term follow-up is necessary. Furthermore, they suggest that an appropriate combination of microsurgical clipping and EVT will provide more effective treatment for patients when it is difficult to select a treatment method due to the

size, shape, and anatomical structure of an aneurysm. After the introduction of EVT in our hospital, 8 patients were treated using the microsurgical clipping and 13 patients were treated using EVT. The trend whereby EVT is the main treatment modality for posterior circulation aneurysms is increasing at our institution. In some institutions, EVT is accepted as the initial treatment method in the posterior

circulation aneurysms. Rooij et al.20) reported that EVT should be the first treatment option for unruptured aneurysms. However, we consider that there are still limitations and complications associated with the use of EVT. Consequently, the criteria used to select between microsurgical clipping and EVT remain a source of controversy and will tend to be resolved on a case-by-case basis. We thought that EVT were not suitable for these patients due to the possibility of high risk of complications and an immediate or delayed failure of complete occlusion for aneurysmal sac.

In one patient (case 8), there was a major risk of occluding the branch during the procedure ; this patient was hence considered to be a candidate for surgery rather than for embolization. Lubicz et al.11) reported that they performed EVT for 9 aneurysms with a branch arising from the sac and that their clinical outcomes were excellent. However, in the angiograms taken following embolization, 5 neck remnants and 2 incomplete occlusions were revealed. In our study, the patient presented with a small bi-lobulated aneurysm (extreme size less than 3 mm in diameter) with a branch arising from the sac. We therefore considered that EVT was not suitable for this lesion because by using EVT it would have been difficult to achieve complete occlusion and preservation of the parent artery. Another patient (case 7) presented with a broad-necked aneurysm that had developed at an acute angle. And 5 patients (case 1, 3, 4, B and M) presented with a broadnecked aneurysms. Coil embolization has limitation in the treatment of broad-necked aneurysms because of possible coil herniation and migration into the parent artery lumen when coils are densely packed on the aneurysm.1)2)7)18)22) Balloon remodeling techniques and stent-assisted coiling have proved to be useful for some broad-necked aneurysms ; however, each of these techniques introduces an additional risk of parent artery ischemia, perforation, distal

thromboembolism, and occlusion of adjacent perforators and branch arteries by the lattice of the stent.4)8)10)18)19)22) In our study, the patient (case 7) presented with a broad-necked aneurysm that had developed at an acute angle and with an SCA diameter of 1.6mm. This lesion was therefore not

suitable for stent-assisted endovascular treatment due to the risk of periprocedural complications.

We also performed microsurgical clipping for 2 patients (cases 5 and 6) with basilar tip, right PICA, right PCA aneurysms. We considered that either EVT or microsurgical clipping would be suitable for these lesions and that there would be no complications. However, the patients were young age and mandatory long-term follow-up would have been necessary if treated by EVT. EVT has important

limitations in that it is associated with a low incidence of total aneurysmal occlusion and can result in a high incidence of recanalization with subsequent aneurysmal rebleeding.16)18)19)22) Taha et al.23) reported 57.5% complete aneurysmal occlusion when using EVT compared with 81.4% with clipping. Further, Paney et al.17) reported that, although EVT leads to approximately 90% of patients achieving independence (GOS I or II), the durability of the EVT remains in question. Additionally, they suggest that

recurrence is related to initial embolization because patients with less than 90% occlusion go on to develop clinically significant recurrence in nearly 60% of the cases. Similarly, Murayama et al.15) suggest that a 55% total occlusion rate and frequent aneurysm recanalization occurred within 3 months after the procedure. In addition, the main difficulty with using EVT compared with microsurgical clipping is

how to decide if a post-EVT remnant is safe to leave or not. We achieved better results in terms of mGOS and the number of postoperative hospital days through the use of 2 treatment modalities, compared to microsurgical clipping only. We accordingly maintain that it is not meaningful to persist with only EVT for posterior circulation aneurysms. In addition to the abovementioned situations, we consider that microsurgical clipping is suitable in patients with less brain swelling, good mentality, and no medical illness addition, whereas EVT is more appropriate for those patients with acute onset hydrocephalus requiring external ventricular drainage, severe brain swelling, poor mentality, and severe medical illness. Further, some authors9)13)22)23) have reported that EVT seems to be more efficacious than microsurgical

clipping in patients who present with a very poor clinical grade after SAH.

Conclusion

We achieved a shortening of the number of postoperative hospital days and a better outcome after applying multimodality treatment for posterior circulation aneurysms.

Furthermore, these results suggest that multimodality management should be considered for better result in the treatment of posterior circulation aneurysms. Thus, although

the trend toward endovascular treatment as the initial aneurysm therapy for posterior circulation aneurysms is also enhancing, we content that neurosurgeons should maintain

the surgical ability for posterior circulation aneurysms.

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