Feasibility of aneurysm clipping via the keyhole approach
This study showed that the operation time in epidural in the keyhole group was significantly shorter than that in the conventional craniotomy group, but no significant difference in the aneurysm clipping (intracranial manipulation) time was observed; this finding indicated that the keyhole approach does not prolong surgery due to the narrow bone hole and that aneurysm clipping with the traditional surgical approach can be carried out smoothly using the keyhole approach. The reason is that with the keyhole approach, only extra space that is basically unnecessary for surgery is removed, while the key operative sites are retained [32]. Intracranial aneurysms are located in the subarachnoid space, and the operating channels for the keyhole approach enter through the gap between the brain tissue and the dura. A gap measuring 2.5 cm can fully meet the exposure requirements of deep structure surgery, and excessive brain tissue traction may cause unnecessary contusion of brain tissue. Designing the surgical approach before surgery is important to facilitate aneurysm clipping. If the aneurysm is oriented laterally, the anterior supraorbital keyhole approach can expose the aneurysm neck well; however, for dorsally oriented aneurysms, fenestration or right-angle clips may be required during the anterior approach (the parent artery may partially obscure the aneurysm clips), and under the lateral pterional keyhole approach, the aneurysm neck can be clearly exposed [18]. In addition to this study, we have successfully performed the keyhole approach on complex aneurysms (large or giant aneurysms, aneurysms in the clinoid segment, and posterior circulation aneurysms), which fully demonstrates that the minimally invasive keyhole approach is effective and feasible for aneurysm clipping [15,16,21]. If necessary, simulated operations can also be performed preoperatively by printing a 3D model of intracranial aneurysms to plan or verify the feasibility of the keyhole approach [14,20].
Effectiveness of aneurysm clipping by the keyhole approach
In this study, aneurysm clipping was successful in all 50 patients who underwent keyhole approach surgery, 44 of whom underwent surgery in the acute stage, while 6/50 patients underwent surgery under the so-called vasospasm period, 10/50 patients experienced intraoperative aneurysm rupture, and 5/50 patients had a Hunt-Hess grade of IV. Therefore, for patients without cerebral hernia before surgery, intracranial pressure can be effectively reduced, and sufficient intracranial operative space is provided through the release of cerebrospinal fluid and the use of dehydrating agents during surgery. Even if the aneurysm ruptures intraoperatively, the bleeding can be quickly controlled with two aspirators, and then, aneurysm clipping can be completed [4,28,37]. One patient with Hunt-Hess grade IV underwent decompressive craniectomy 2 days after surgery in the acute stage because of high intracranial pressure caused by cerebral vasospasm and recovered well after hyperbaric oxygen therapy, indicating that in some patients with severe subarachnoid hemorrhage and poor preoperative grading, traditional bone flap craniotomy and decompressive craniectomy should be performed early depending on their conditions.
Comparison of the keyhole approach and conventional craniotomy
The duration of epidural operation in the keyhole group was on average 40 minutes shorter than that in the conventional craniotomy group, and the hospitalization time was 1 week shorter, enabling the surgeon to spend more time and energy on the treatment of intracranial lesions and allowing the patient to recover and return home as soon as possible. Therefore, the treatment costs were also lower.
The greatest difference between the keyhole approach and conventional craniotomy is the extent of the surgical trauma and related injuries. Some people may think that a larger surgical incision is not harmful to the patient, but in fact, the psychological fortitude of the patient and the postoperative impact are substantially affected by the incision size. Two patients in the conventional craniotomy group had postoperative intracerebral hematoma due to brain traction and contusion. In contrast, the small bone holes of the keyhole approach can limit the traction on brain tissue. In addition, the incidence of postoperative infections and epilepsy in the conventional group was higher than that in the keyhole group. One patient had undergone clipping of a posterior communicating artery aneurysm through conventional craniotomy in another hospital one year previously. After surgery, the patient had obvious feelings of discomfort and then suffered from temporal muscle atrophy with a sunken appearance after discharge. The patient was admitted to our department because of rupture of a contralateral posterior communicating artery aneurysm and was treated by the pterional keyhole approach (Figure 1 D-E). After surgery, the patient felt well and happy, with no defects in appearance, and considered that the keyhole approach was quite different from conventional craniotomy. Many patients with aneurysms choose interventional surgery because they are afraid of conventional craniotomy. The minimally invasive nature of the keyhole approach can increase their acceptance of microsurgery [1,7,31].
Indeed, small bone holes are required with minimally invasive keyhole approach, which may cause some discomfort to surgeons who are familiar with conventional craniotomy. In fact, in the past, when conventional craniotomy was performed, the actual operating space was fairly similar to that of the keyhole approach, and experienced aneurysm surgeons do not experience difficulty when trying different surgical approaches. Young surgeons can quickly master the keyhole approach after training in microanatomy or under the guidance of surgeons familiar with the keyhole approach. The disadvantage of the keyhole approach is that it is limited to a narrow cranial hole, and changing the direction of the aneurysm clip during the surgery is difficult [25,29,34]. Under a fixed operating angle, surgeons can only rely on different aneurysm clips and adjustment of the operating table to reach the best clipping angle. For some complex aneurysms, if multiangle observation or clipping is required, conventional craniotomy is favorable.
Comparison of the keyhole approach and endovascular treatment
For interventional therapy, no open injury or blood transfusion is required, and the incidence of postoperative infection and epilepsy is low [9,10,12]. This advantage of endovascular treatment was also confirmed by this study.
The response to aneurysm rupture during surgery is one of the key factors affecting the efficacy of aneurysm surgery. The countermeasures in conventional craniotomy are all suitable for the keyhole approach [11,13]. In this study, 10 aneurysms in the keyhole group and 11 aneurysms in the conventional craniotomy group ruptured during surgery, and the bleeding was always quickly and properly controlled, without complications caused by poor management of ruptured aneurysms. However, aneurysm rupture during endovascular treatment is very different and is often fatal, and no rapid and effective treatment methods are available [33,36]. In the endovascular treatment group of this study, although eight patients with intraoperative aneurysm rupture received rapid hemostasis by rapid coil packing, four had increased intracranial pressure and brain swelling after surgery and underwent emergency conventional craniotomy. Among them, two patients died, resulting in a mortality rate of intraoperative rupture of 25% (2/8).
The rapid development of endovascular treatment techniques has expanded the indications for the treatment of intracranial aneurysms [25], but at present, some aneurysms are better suited for surgical clipping. For example, for wide-necked aneurysms, no subsequent treatment of double antiplatelet due to stent implantation during endovascular treatment is required after surgical clipping; for patients with obvious intracranial hemorrhage, the hematoma can be removed and decompressed at the time of surgical clipping, or the hemorrhagic cerebrospinal fluid can be fully released to reduce the incidence of vasospasm and hydrocephalus; clipping and shaping of giant aneurysms can achieve a great effect; and surgical clipping is still a better option for patients with intracranial arterial tortuosity and for aneurysms that are hard to reach with the catheter guide wire [5,22,23,35]. For long-term efficacy, endovascular treatment still has a certain recurrence rate. In this study, DSA at the 6-month follow-up showed that three of the 35 aneurysms with simple coils had recurrence (8.57%), even if they reached Raymond grade I occlusion after the surgery. Microsurgical clipping of intracranial aneurysms is still a key treatment technique, but we also need to adapt to new advancements and make aneurysm clipping more minimally invasive, for which the keyhole approach is currently the most representative, optimal choice [3,17].