Introduction

Basilar apex aneurysms are rare. They are difficult to access due to their location and have a tendency to bleed (1,2). These aneurysms are located in a deep area that can only be reached through a narrow corridor that contains cranial nerves that are vitally important. Also, deep feeders arising from this area feed the brainstem (3). All of these features complicate surgery involving a basilar apex aneurysm. Although it is easy to reach these areas with endovascular treatments, this method has an occlusion rate of about 68% in aneurysms with wide necks and a high rate of a second bleeding, which poses additional risks for the patient (4). Large aneurysms, aneurysms with wide necks and aneurysms with posterior projection and anatomical variations (fenestration, high or low location of the dome of aneurysm) further complicate an already difficult surgery (5). In addition, if the patient has multiple aneurysms, a very intricate situation occurs. These factors have led to an increase in the use of different methods to facilitate basilar apex aneurysm surgery to ensure complete occlusion. In this article, we share our experiences related to 16 basilar apex aneurysms that were treated in our institution for which different surgical approaches were used.

Materials and Methods

Of the 38 basilar apex aneurysms detected between October 2017 and January 2020. Twenty-two of these patients were treated endovascularly. Endovascular treatment was performed in patients with elderly, comorbid diseases and those who thought that proximal control would be difficult. Sixteen patients that underwent surgery were included in this study. The demographic data of those that were included in the study were recorded. Patients who had ruptured aneurysms had head computed tomography (CT) scans, and GCS and Fischer scores were recorded. All of the patients underwent digital subtraction angiography (DSA) and the localisations and size of their aneurysms, the presence of multiple aneurysms and the anatomical variations were revealed (Figure 1,2). CT angiography was also done on the patients to determine the location of the dome in relation to the sella (Figure 3). The aneurysms with wide necks or with posterior projection, large aneurysms and those with anatomical variations (fenestration, high and low location of the dome in relation to the sella) were categorised as complex aneurysms. The surgical approach to be employed for the patient was determined according to these findings. Follow-up DSAs were done on the 1^st-3^rd days after the operation to check the occlusions of the aneurysms (Figure 4). The modified Rankin scores of the patients after their follow-up for 2-16 months were recorded.

Results

Five of the patients were male, 11 were female and the average age was 48.3 (age range, 20-74 years). While 12 of the patients presented with subarachnoid haemorrhage (SAH), four of the patients were detected incidentally. The GCS was detected to be 14 for four of the patients who presented with SAH, 13 for four of the patients, 12,11,9 and 8 for one patient each. Seven patients were described as having a complex aneurysm. The FROZ approach was employed for five of these patients (Figure 5), the PT approach for two of the patients and the pterional approach was used for the rest. Multiple aneurysms were detected in six patients and the accompanying aneurysms were of the anterior communicating artery (Acom A), the middle cerebral artery, the posterior communicating artery (Pcom) and the internal carotid artery. All of the aneurysms were clipped. However, the aneurysm could not be completely closed in a wide-necked aneurysm and wrapping was done. Complications developed in six of the patients (hydrocephaly, vasospasm, deep feeder ischaemia, oculomotor nerve involvement, per-op haemorrhage). The patients underwent a follow-up DSA on the 1^st-3^rd post-operative days. Complete occlusion was observed in all of the aneurysms except the aneurysm that underwent wrapping. Two of the patients died, and in the 2-16 months follow-up of the other 14 patients, the mRS was detected as 0 in five patients, 1 in six patients, 2 in one patient, and 3 in two patients (Table 1).

Discussion

The surgical treatment of basilar apex aneurysms began with the description of the microsurgical approaches that could be applied in this area by Drake (6) and Yasargil et al. (7). In this situation, the surgical field is very narrow and proximal control is difficult. The rate of complications is higher when compared with anterior circulation aneurysms. It is difficult to observe and spare the perforating arteries during the clipping of the aneurysm. Because of these complications and with the development of other options for treatment, endovascular treatments have become preferable for aneurysms in this region. Recanalisation rates have been found to be low for narrow-necked aneurysms with small diameters (8). However, occlusion rates have been observed to decrease to as low as 57% in wide-necked and partially thrombosed aneurysms with large diameters (9). Complete occlusion of aneurysms in this region is very important because the re-bleeding rates are high. Therefore, the interest in surgical approaches has increased over time.

Progress in imaging techniques has clearly revealed the relationship of aneurysms with the sella and the clivus, and different microsurgical techniques have been proposed according to the location of the aneurysm. Several techniques that have been recommended include the pterional approach for basilar apex aneurysms with high and normal locations, the pretemporal, trans-cavernous approach for those with a retrosellar location and the middle fossa approach and petrosectomy for those with a sub-sellar location (10-12).

Nanda et al. (5) described other posterior circulation aneurysms, brain oedema and highly located and large aneurysms as complex aneurysms. Different surgical approaches were recommended for these aneurysms. Of the 33 patients in their study, the transcavernous approach was used for four patients, the sub-temporal approach for six patients, the pterional approach for eight patients, the “half and half” approach for eight patients and the FTOZ approach was used for seven patients, and they reported that good outcomes were achieved in 71.9 % of the patients. In their study, Higa et al. (13) detected multiple aneurysms in 32% of the cases. In our study, we detected multiple aneurysms in six of the 16 patients (37%), and all of the additional aneurysms were located in the anterior circulation. We believe that the surgical procedures for these aneurysms also contributed to the morbidity and mortality of the patients. Therefore, we think that the aneurysms that were located in the anterior location accompanying the basilar apex aneurysm should have been included in Nanda et al. (5) description of complex aneurysms.

Lozier et al. (14) studied 98 patients and stated that non-giant basilar apex aneurysms could be operated on with a 90% expectation of a good outcome, and that if the aneurysm was un-ruptured as well as non-giant, the success rate increased to 97%. The mortality rate in this study was 6.1%. Also, in this study, it was emphasised that the long-term reason for mortality and morbidity was perforation of an artery.

Hernesniemi et al. (15) stated that the sub-temporal approach was a simple and efficient method for treating basilar apex aneurysms regardless of the size, location, and projection of the aneurysm and that posterior clinoidectomy and petrosectomy were not needed.

Sanai et al. (16) reported 97% complete occlusion, 57% good discharge scores and 10.5% mortality in their study of 96 patients with basilar apex aneurysms on whom they performed operations using mostly the pterional and orbitozygomatic approaches. Krisht et al. (17) performed surgery on 50 complex basilar apex aneurysms using the transzygomatic and pretemporal transcavernous approaches. They reported 98% complete occlusion, 88% good outcomes and 2% mortality of the patients.

Endovascular treatment is another alternative for the treatment of basilar peak aneurysms. In their study, Abecassis et al. (18) emphasized that recurrence rate is higher in endovascular treatment compared to surgery, but costs are lower and patient outcome scores are better.

In our study, we performed surgery on 16 patients, and four of the patients had been detected incidentally. Two of the patients died (12%). Seven of our patients had findings in accordance with the description of a complex aneurysm. The patients who fulfilled the definition of a complex aneurysm underwent an operation using the FROZ or pretemporal approach according to the location of the aneurysm, and the others experienced the pterional approach. When necessary, the anterior and posterior clinoid processes were drilled to provide an area to see and clip the aneurysm. In accordance with the studies in the literature, the discharge scores of the patients with un-ruptured aneurysms who did not have the characteristics of a complex aneurysm were better. Again, in accordance with the literature, the factor that increased the mortality and morbidity the most was damage from perforating an artery. The complete occlusion rate was 93%, and 68% of the patients had good discharge scores (mRS 0,1). We attribute the high rate of death and the low rate of good discharge scores to the small number of patients and the high number of multiple aneurysms.

Conclusion

The hemodynamics and the progression of posterior circulation aneurysms are different than with anterior circulation aneurysms. The fact that the aneurysm is located in a narrow corridor with the presence of perforating arteries of vital importance affects the mortality and morbidity of the patients. A good evaluation of the basilar apex aneurysm in the pre-operative period is very important to select the appropriate surgical technique. When aneurysms that are not complex are operated on with the appropriate methods, favourable results are achieved. Although recently endovascular methods have been the preferred treatment for basilar apex aneurysms, the inability to ensure complete aneurysm occlusion and the risk of thromboembolism sometimes prevents the use of this method. The correct approach is to make a patient-based evaluation and to choose the most appropriate treatment method.

Ethics

Ethics Committee Approval: Adana City Training and Research Hospital Ethics Committee (date: 03. 04. 2020, no: 902).

Informed Consent: Informed consent was obtained.

Peer-review: Externally peer-reviewed.

Financial Disclosure: The author declared that this study received no financial support.