Fully endoscopic keyhole approach for intracranial aneurysm clipping: clinical outcomes and technical note

Abstract

Background

Surgical clipping is often utilized to treat intracranial aneurysms. The application of the endoscopy and keyhole approach in neurosurgery is increasing gradually in intracranial aneurysm occlusion. The aim of this study is to evaluate the role of fully endoscopic keyhole approach in clipping of intracranial aneurysms.

Methods

We retrospectively analyzed four cases of intracranial aneurysms, including three cases of middle cerebral artery bifurcation aneurysms (M1) and one case of anterior communicating aneurysms (ACoA). Among them, the anterior communicating aneurysm underwent fully endoscopic clipping via supraorbital keyhole approach and the middle cerebral aneurysms underwent fully endoscopic clipping via mini-pterional keyhole approach. The clipped aneurysms were evaluated by Digital Subtraction Angiography (DSA).

Results

All patients had satisfactory cerebral aneurysm clipping via the endoscopic keyhole approach. There was no cerebral hemorrhage, cerebral infarction, cerebral vasospasm. One case of intracranial infection was cured by active anti-infection. No recurrence of aneurysms after 6 months of follow-up.

Conclusion

With the advantages of the endoscopy and keyhole approach, the excellent visual field of the endoscope can reduce the influence of intracranial aneurysmal neck residual and perforating vessel. However, endoscopic clipping of intracranial aneurysms in narrow corridors requires a learning curve.

Background

The intracranial aneurysm, often described as a"ticking time bomb"within the human body, poses a critical threat due to its potential rupture. Such an event triggers a severe cascade of physiological complications, resulting in alarmingly high rates of disability and mortality [1]. Consequently, timely intervention for aneurysm management is imperative. Current mainstream therapeutic strategies include minimally invasive surgical clipping and endovascular procedures. Recent advancements in endovascular technologies, particularly the evolution of embolization coils and flow diverters, have significantly expanded treatment options for some elderly populations and anatomically complex aneurysms. Concurrently, refined microsurgical methodologies—such as keyhole craniotomies and endoscopic-assisted clipping—are increasingly being integrated into neurosurgical practice. Collectively, these innovations have substantially enhanced the safety profile and minimally invasive nature of contemporary aneurysm management.

Surgical clipping, as a definitive treatment for intracranial aneurysms, entails performing a craniotomy to retract brain tissue and directly visualize, dissect, and occlude the aneurysm. The introduction of the surgical microscope revolutionized aneurysm clipping by providing enhanced illumination and magnification, enabling surgeons to precisely approach and exclude aneurysms. Concurrent advancements in aneurysm clip design have further facilitated safe dissection of the aneurysm neck while preserving adjacent neurovascular structures [2, 3]. Over the years, keyhole techniques derived from the standard pterional approach, including the supraorbital and mini-pterional approaches, have been also utilized in aneurysm clipping procedures [4]. These minimally invasive approaches minimize temporal muscle retraction, reduce brain tissue exposure, shorten operative trajectories, and mitigate neurovascular disruption, thereby improving outcomes while maintaining efficacy. Nevertheless, craniotomy-related challenges persist, particularly in elderly patients or those with comorbidities. Potential complications include intracranial hemorrhage, infection, brain contusion from excessive retraction, and impaired scalp wound healing, all of which may compromise treatment outcomes [5]. In contrast, the evolution of neurointerventional technologies (e.g., detachable coils and flow diverters) has propelled endovascular therapy to the forefront of aneurysm management. While this approach circumvents craniotomy-associated risks, it introduces concerns such as aneurysm recanalization, long-term antiplatelet therapy requirements, and elevated procedural costs.

Although intracranial aneurysm clipping remains one of the most effective treatment methods, there is also a certain residual rate of aneurysm neck and a certain rate of blockage or stenosis of carrier and perforator vessels under linear visual field [6, 7]. Clinically, Doppler sonography and intraoperative indocyanine green angiography are employed to evaluate aneurysm occlusion and patency of peripheral vascular after surgical clipping. Nevertheless, these modalities are constrained by their reliance on direct-line visualization, which restricts evaluation of anatomical regions behind the aneurysm and adjacent neurovascular structures. Recent advancements in endoscopic technology have expanded its utility in intracranial surgery. The benefits of the endoscopy, such as panoramic view and multi-angle observation, have also been applied to aneurysm surgery [8]. The flexible visual field of the endoscope can effectively display the characteristics of aneurysmal sac and related vessels during surgical clipping.

“Keyhole surgery” has been widely utilized in intracranial aneurysm clipping. Keyhole surgery is not only reflected in the small surgical incision and craniotomy, but also in the effective exposure of the surgical area of interest with minimal trauma [9]. The minimization of brain trauma in keyhole surgery combined with the advantages of endoscopic illumination and multi-angled view makes surgical clipping more minimally invasive [10].

Endoscopic keyhole neurosurgery has emerged as a valuable adjunct to microsurgical clipping, potentially enhancing treatment outcomes for intracranial aneurysms. However, there are few reported studies on fully endoscopic keyhole approach to clip intracranial aneurysms. Therefore, this study summarized the experience of fully endoscopic keyhole approach in clipping intracranial aneurysms and provided diversity of treatment options for intracranial aneurysms.

Patients and methods

Four cases of intracranial aneurysms undergoing fully endoscopic clipping were retrospectively analyzed between September 2022 and October 2023. Inclusion criteria were as follows: 1. Unruptured anterior circulating aneurysm; 2. After communication, the patients'families were willing to choose aneurysm clipping; 3. After evaluation, they had no serious diseases and could tolerate surgery. The demographic and clinical characteristics of the patients were shown in Table 1. In all patients, the location, size, shape, direction, carrier vessel, perforator vessel, etc. of aneurysm were confirmed by Digital Subtraction Angiography before surgery. Postoperative cerebral hemorrhage, cerebral infarction, vasospasm, neurological deficit, intracranial infection, and recurrence during follow-up were recorded.

Table 1 The demographic and clinical characteristics of the patients treated with intracranial aneurysmal clipped operation

Surgical procedure

Endoscopic eyebrow keyhole approach for anterior communicating aneurysms:

The room was set up with the surgeon and assistant at the head of the patient, the anesthesia machine at the foot of the patient, and the instrument nurse at the opposite side of the surgeon. After satisfactory anesthesia, the person was positioned in a supine position. The head is fixed in the DORO head frame and extended by 20–30°. Routine disinfection was performed. One eyebrow arch incision was made from the frontal bone horn process to the medial supraorbital nerve, and each skin layer was cut in turn. The electric knife was used to cut the frontal muscle in an arc, a small drill was used to open a small hole in the skull, and a small free bone flap (2.5 × 2.0 cm) was formed by milling the skull with a milling cutter. Bone flap as close to the anterior skull base as possible. The open frontal sinus was completely sealed with bone wax. The surgeon and assistant were on the diseased side of the patient's head, and the endoscopic display was opposite the surgeon. The dural membrane was cut in the arc of the frontal base, and a 30° rigid endoscopy (Karl Storz) were placed in the surgical area after adequate release of cerebrospinal fluid. An assistant held the endoscope and adjusts it dynamically as needed. The surgeon held the aspirator in one hand and other instruments in the other. After satisfactory decrease of cerebral pressure, the automatic cerebral platen lifted the frontal lobe and inserted endoscopy to probe the sellar region, bilateral optic nerve, optic chiasma, and internal carotid artery. The anterior cerebral artery was found in the distal exploration along the internal carotid artery, and the anterior communicating artery was continued to be explored. The obvious cystic bulge of the aneurysm was found at the anterior communicating artery. The anterior cerebral A1 segment was temporarily blocked first, and after the aneurysm was completely isolated and exposed, the aneurysm clip was applied to clip the aneurysm. After confirming that the clipping was reliable, the dura was closed in a watertight fashion. The bone flap was fixed. The skin was sutured. The main surgical procedures are shown in Fig. 1.

Fig. 1

Major steps during the endoscopic eyebrow keyhole approach clipping of anterior communicating aneurysm. A Three-dimensional angiography showed the anterior communicating aneurysm. B Surgical eyebrow incision. C The carotid cistern was opened to expose the internal carotid artery and anterior cerebral artery. D Aneurysm was then dissected. E–G The aneurysm was clipped and visualized with the Yasargil clip (blue five-pointed star). H Postoperative digital subtraction angiography showed a well-clipped aneurysm with no residual filling. I The extent of the bone window under the endoscopic view. J, K Postoperative CT scan indicated the extent of the craniotomy (green circle)

Endoscopic mini-pterional keyhole approach for middle cerebral artery bifurcation aneurysms:

The room was set up with the surgeon and assistant at the head of the patient, the anesthesia machine at the foot of the patient, and the instrument nurse at the opposite side of the surgeon. After satisfactory anesthesia, the person was positioned in a supine position with the head slightly tilted 30 degrees to the opposite side. The head is fixed in the DORO head frame, and routine disinfection was performed. A small curved incision was made within the hairline centered on the sphenoid ridge. The angle of the curve at both ends was greater than 120°. Each skin layer was incised successively, and the incision was extended. The temporal muscle was dissected with an electric knife. A bone hole was ground with a drill. A small bone flap (3.0 × 2.0 cm) was mused with a milling cutter. The dura was dissected in a curvilinear fashion. The sphenoid ridge was thoroughly smoothed with a drill. The surgeon and assistant were on the diseased side of the patient's head, and the endoscopic display was opposite the surgeon. The 30° rigid endoscopy (Karl Storz) was held by an assistant. The surgeon held the aspirator in one hand and other instruments in the other. The sylvian fissure and carotid cisterna were opened under endoscopic vision to fully release cerebrospinal fluid. The optic nerve, the internal carotid artery, and the M1 segment of the middle cerebral artery are revealed. Then the parental artery, perforating artery and aneurysmal sac were dissected and separated. The aneurysm was found at the M1 branch of the middle cerebral artery. The neck of the aneurysm was clipped with a permanent aneurysm clip. The dural was sutured watertight. The bone flap was fixed. The skin incision was closed in layers. The main surgical procedures are shown in Fig. 2.

Fig. 2

Major steps during the endoscopic mini-pterional keyhole approach clipping of a middle cerebral artery bifurcation aneurysm. A Three-dimensional angiography showed the middle cerebral artery bifurcation aneurysm. B Surgical skin incision. C The sylvian fissure and carotid cistern were opened to expose the internal carotid artery and its bifurcation. D Aneurysm was then dissected. E–G The aneurysm was clipped and visualized with the Lazic aneurysm clip (blue five-pointed star). H Postoperative digital subtraction angiography showed a well-clipped aneurysm with no residual filling. I The extent of the bone window under the endoscopic view. J, K Postoperative CT scan indicated the extent of the craniotomy (green circle)

Results

The average age of all patients was 60 years, including three women and one man. These patients had unruptured aneurysms. Aneurysms were evaluated by DSA before surgery. There were three cases of middle cerebral artery proximal aneurysms (M1) and one case of anterior communicating aneurysms (ACoA). Among them, the anterior communicating aneurysm underwent fully endoscopic clipping via supraorbital keyhole approach and the middle cerebral aneurysms underwent fully endoscopic clipping via mini-pterional keyhole approach. All aneurysmal necks were completely clipped under the endoscopic view. There was no residual aneurysmal neck after clipping. There was no stenosis or occlusion of the surrounding blood vessels. There were no intracranial hemorrhage, cerebral infarction or vasospasm after operation. One patient developed postoperative pyrexia (> 38.5 °C) with cerebrospinal fluid (CSF) analysis via lumbar puncture suggestive of intracranial infection. Although CSF routine examination and bacterial culture were performed, microbiological studies yielded negative results. Empirical antimicrobial therapy was initiated with intravenous meropenem and vancomycin, adjusted according to renal function. Follow-up CSF analysis demonstrated normalization of biochemical parameters and sterile cultures, confirming resolution of the intracranial infection. The follow-up time was more than 10 months, and there was no recurrence of aneurysm during the follow-up.

Discussion

At present, the main treatment methods for intracranial aneurysms are clipping surgery and endovascular therapy [11, 12]. Both of these methods aim to completely occlude the aneurysm through a minimally invasive method without affecting the parent artery and perforating vessels. With the innovation of neurointerventional materials, endovascular treatment of intracranial aneurysms has become more and more popular. At the same time, with the development of skull base surgery and the use of tools such as microscopy and endoscopy, some surgery-related trauma and complications have been reduced [13]. The focus of intracranial aneurysm treatment is to have no residual aneurysm of the neck and not affect the blood flow of important vessels. Residual aneurysms in the neck can cause recurrence, and narrowing of the parent's blood vessels and perforator vessels may lead to unintended consequences. The same is true for surgical clipping. One of the reasons for this is that the tubular field of view of the microscope is not sufficient to visualize the aneurysm sac and its surrounding blood vessels. Endoscopic technology can compensate for that shortcoming.

The goal of aneurysm clipping is to have an excellent occlusion rate with minimal perioperative complications and a favorable postoperative neurological prognosis. With endoscopic advantages, many studies have reported the feasibility and effectiveness of endoscopy in aneurysm clipping [14, 15]. First of all, on the basis of conventional minimally invasive craniotomy, endoscopic close-up observation, panoramic field of view and good lighting make the brain tissue pull less and the surgical field of view clear. Secondly, the characteristics of multi-angle observation and panoramic field of view of the endoscope allows for better visualization of aneurysm morphology and the anatomical relationship between the adjacent nerve and blood vessels with little disturbance to the surrounding tissues. While clipping the aneurysm completely, it can ensure the patency of the carrier artery and perforator vessels, and reduce ischemia and vasospasm [16].

With the development of minimally invasive neurosurgery, the evolution of some surgical approaches and the innovation of surgical instruments have brought benefits to the prognosis of patients. Compared with the traditional craniotomy, some minimally invasive keyhole approaches have some advantages in the treatment of vascular diseases [17]. The first is the reduction of unnecessary exposure to brain tissue, reducing brain tissue trauma and bleeding. We are just trying to properly expose the surgical area of interest, and reduce the retraction. For narrow surgical areas we can also use endoscopes to increase lighting and obtain close observation. Secondly, reducing operation time also increases patient safety. Finally, small surgical incisions can optimize cosmetic results and increase patient acceptance of the procedure. The introduction of Axel Perneczky's keyhole approach concept into aneurysm surgery also makes the surgical treatment of aneurysms more minimally invasive [18, 19]. The most representative of these are the supraorbital keyhole craniotomy and mini-pterional approaches. They can allow the surgeon to fully clip the aneurysmal neck while ensuring the full use of the surgical field, and reduce the traction damage to the surrounding tissue. In this study, all aneurysms were completely clipped through keyhole approach under complete endoscopy, and there were no postoperative deaths, cerebral hemorrhage, or cerebral infarction. One patient suffered from an intracranial infection and was cured with aggressive anti-infective therapy. None of the aneurysms recurred during follow-up. Minimally invasive is a concept, of course. Based on a disease characteristic, we need to personalize the minimally invasive surgical approach. For suitable patients, minimally invasive craniotomy can reduce unnecessary exposure of brain tissue and reduce operation time, which is beneficial to the prognosis of patients. However, for some patients with cranial hypertension, we cannot choose a small incision for the minimally invasive craniotomy. The most important thing is to carefully formulate a surgical plan according to the characteristics of the lesion and their own surgical techniques.

At the same time, it is crucial to correctly place the aneurysm clip and adjust the angle between the clip and the aneurysm neck when using different aneurysm clips. With the gradual improvement of the material and biological characteristics of aneurysm clips, it also affects the effect of aneurysm clipping to a certain extent. The main aneurysm clips in common use today are the Yasargil clip and Sugita clip [20]. Because the clip appliers are on the outside of the aneurysm clip, the surgeon can more easily observe the condition of the aneurysm and surrounding blood vessels during surgery. In addition, an external brace design often provides better stability, especially when clipping large or complex aneurysms. Of course, due to the position of the holder, more angular adjustments may be required, which may increase the complexity of the procedure. In the process of operation, the surgical field of view may be blocked to a certain extent, and affect the accuracy of operation. In recent years, another innovative aneurysm clip is the Lazic aneurysm clip system, also known as the"L"aneurysm clip [21]. Allowing a large angle between the clip applier and the aneurysm clip facilitates surgery in complex locations. Because the clip applier is located on the inside, the occlusion of the surgical field is small, which is convenient for fine operation. However, the application of L aneurysm clip requires high surgical skills and requires the surgeon to have a high degree of proficiency to master it. Moreover, it may not be as stable as an externally supported aneurysm clamp during prolonged surgery or intensive procedures.

It is well known that microscopic clipping and endovascular therapy are commonly used for aneurysm treatment. Only a few cases of fully endoscopic treatment of intracranial aneurysms have been reported, and all have achieved excellent results [22]. Xie et al. reported 7 cases of fully endoscopic clipping aneurysms, and postoperative examination indicated complete occlusion of the aneurysms, and the patients had a good prognosis [23]. Their experience was that the surgeon's bimanual operation and the assistant holding the endoscope provided great flexibility for clipping aneurysms. Moreover, the endoscopic view could provide high-quality display of fine structures and some hidden anatomical details. The multi-angle flexibility of endoscopy compensates for the linear field of view of the microscope. Its panoramic field of view and illumination make the observation of the aneurysm and surrounding tissue much comprehensive with less traction.

In recent years, microvascular Doppler sonography and intraoperative indocyanine green angiography have also been used to evaluate the effect of aneurysm clipping [24, 25]. Although Doppler ultrasound can provide information such as evoked potentials and blood flow monitoring, it cannot assess whether there is residual aneurysm. The endoscope, however, provides a good visualization of the morphology of the clipped aneurysm [26]. In addition, although intraoperative indocyanine green angiography can show the evaluation of the clipped aneurysm and perforating vessels after clipping the aneurysm, it also cannot show the residual status of the aneurysm neck, and the observation of the peripheral arteries may be affected by the interference of the aneurysm clip [27]. However, the advantages of endoscopic close-up observation, wide-angle observation, panoramic field of view and excellent illumination can effectively evaluate aneurysm morphology and peripheral vasculature and nerves with slight traction of the surrounding tissue compared to the microscope. Its high-quality visual field observation by endoscope can show the morphology of clipped aneurysm and the situation of neighboring vessels, which can increase the safety and effectiveness of aneurysm clipping treatment.

When managing patients without severe intracranial hypertension or cerebral edema, some experienced neurosurgeons may choose minimally invasive approaches such as the supraorbital keyhole and mini-pterional approaches for aneurysm clipping. These refined procedures aim to minimize unnecessary brain tissue exposure and optimize cosmetic outcomes while maintaining therapeutic efficacy. The advantages of keyhole approach are not only reflected in the small incision, small bone flap and less brain tissue exposure, but also reflected in the cosmetic incision, small brain tissue retraction and excellent aneurysm clipping rate. One study reported that the supraorbital keyhole approach was utilized to treat 1457 intracranial aneurysms, with a clipping rate of 99% and a good neurological outcome in 93% of patients [28]. Another study suggested that the mini-pterional keyhole approach was also a safe and effective microinvasive method for clipping middle cerebral artery aneurysms [29]. Although the keyhole approach offers minimization of surgical craniotomy, traumatization, and enhanced post-operative neurological recovery, its narrow operating pathway increases the requirements of the surgeon's aneurysmal clipping technique, and poses challenges for the illumination and visualization of the surgical field of view. However, with the development of the endoscope, its good lighting, close observation, angle observation and other characteristics play a complementary role. Of course, fully endoscopic keyhole approach for intracranial aneurysm clipping has certain indications, and it is important to select appropriate patients. It mainly applies to unruptured aneurysms of the anterior cerebral circulation. Preoperative assessment of the high risk of aneurysm rupture should also be carefully selected to avoid difficulties in intraoperative clipping during rupture. In addition, for patients with ruptured aneurysms with high Hunt-Hess grade, clipping aneurysms in narrow operating corridor presents challenges due to high intracranial pressure. There is also a long learning curve for the surgeon's experience with aneurysm clipping and endoscopic techniques in narrow corridors. In conclusion, compared with endovascular therapy and traditional craniotomy for the treatment of intracranial aneurysms, this method gives the surgeon an additional treatment option.

Limitations

There are some shortcomings in this study. First, endovascular treatment of cerebral aneurysms is just mainstream in medical centers with robust technology. Due to the high cost of endovascular treatment materials, minimally invasive clipping aneurysms remains the cornerstone in the case of low income. However, there are few studies on fully endoscopic keyhole approach for the treatment of cerebral aneurysms, and the clinical efficacy is uncertain. Secondly, the number of clinical cases in this study is small, and more suitable patients need to be screened at a later stage to bring more experience through long-term follow-up.

Conclusion

On one hand, the endoscope has the characteristics of multi-angle observation, close observation and good illumination. On the other hand, keyhole approach has the minimization of cosmetic incision, traumatization and brain tissue exposure. With the excellent visualization of the endoscope, the neck of aneurysm can be effectively clipped in the narrow surgical channel, and the morphological characteristics of the aneurysm after clipping, as well as the parental vessels and perforating vessels can be flexibly observed. However, endoscopic clipping of intracranial aneurysms in narrow corridors requires a learning curve.