Abstract

Background: Modified cranial approaches for vascular pathology are sometimes necessary to enhance exposure and can be tailored by the pathology treated and surgical conditions. The authors outline these approaches, comparing the advantages and disadvantages of each.

Methods: Surgical footage of the senior author performing cranial-orbital skull base approaches for intracranial aneurysms as part of routine care was reviewed to identify and describe the advantages and disadvantages of these approaches to vascular pathology. The variations of cranial-orbital approaches included supraorbital, lateral supraorbital (LSO), orbito-pterional, cranio-orbital, and transcavernous approaches. Four illustrative cases are included. The literature was also reviewed for a concise compilation and summary of technical considerations and comparisons of cranial-orbital approaches for the microsurgical treatment of vascular pathology.

Results: The supraorbital approach provides a trajectory along the orbital roof, allowing access to anterior circulation aneurysms without drilling the anterior clinoid process. While this approach is suited for inferiorly and anteriorly projecting anterior communicating artery (AcomA) aneurysms, orbito-pterional approaches are better suited for superiorly projecting AcomA aneurysms. The LSO approach allows access to anterior circulation and low-lying basilar apex lesions. The orbito-pterional approach is an “outside-in” approach to access the intracranial space from the orbit; the cranio-orbital approach is considered an “inside-out” approach to access the orbit from the intracranial space.

Conclusion: Modifications of the traditional pterional craniotomy are useful for various anterior and posterior circulation vascular pathologies. Extensions of these surgical corridors with transcavernous approaches can also be useful. Understanding the advantages and disadvantages of each is important in optimal approach selection.

Keywords: Cranio-orbital approach, Neurovascular, Orbito-cranial approach, Skull base, Supraorbital, Transcavernous approach

INTRODUCTION

Cranial approaches for vascular pathology often incorporate a skull base osteotomy or approach. The long established pterional – or fronto-temporal – approach was described by Dandy in 1922, and its cranial-orbital variations continue to be a workhorse for approaching intracranial vascular pathology.[ 11 ] Modifications, such as the half-and-half (a combination of pterional and subtemporal approaches) or orbito-zygomatic approaches, are sometimes necessary to enhance exposure. These approaches can be adapted for the pathology treated and the surgical conditions. The current literature explaining how and why to select a cranial-orbital approach for treating vascular pathology is sparse.[ 2 , 3 , 5 , 6 , 8 , 10 , 14 , 17 , 18 , 22 , 24 , 26 , 29 ] This paper, therefore, will concisely describe cranial-orbital approaches to vascular pathology and the advantages and disadvantages of each approach for specific commonly encountered clinical scenarios and intracranial vascular targets. Illustrative case examples will highlight the utility of these variations. Understanding how to effectively tailor cranial-orbital skull base approach corridors for optimal access to vascular lesions is important for efficient access and safe treatment.

MATERIALS AND METHODS

We identified commonly employed cranial-orbital skull base approaches for treating vascular pathology. The main variations of cranial-orbital approaches included supraorbital, lateral supraorbital (LSO), orbito-pterional, cranio-orbital, and transcavernous approaches. Cases performed by the senior author utilizing these approaches as part of routine care were identified. (Case surgeries are routinely recorded in our practice for later review and to improve surgeon performance.) Surgical footage of representative cases was reviewed to identify and describe the advantages and disadvantages of each approach for specific anatomical pathology and locations. Finally, we reviewed the literature for a concise compilation and summary of previously described technical considerations and comparisons of cranial-orbital approaches for the microsurgical treatment of vascular pathology.

RESULTS

The supraorbital approach provides a trajectory along the orbital roof and access to anterior circulation aneurysms that do not require extensive drilling of the anterior clinoid process. The superior extension of the trajectory is limited by the orbital rim, which can also be removed as needed. This approach is well suited for inferiorly and anteriorly projecting anterior communicating artery (AcomA) aneurysms and select paraclinoid aneurysms.[ 5 , 6 , 8 , 10 , 14 , 17 , 18 , 22 ]

The orbital extensions of pterional approaches are better suited for superiorly and posteriorly projecting AcomA aneurysms that often need considerably more dissection in the interhemispheric fissure.[ 22 ] The orbito-pterional approach is an “outside-in” approach to access the intracranial space from the orbit, while the cranio-orbital approach is considered an “inside-out” approach to access the orbit from the intracranial space without removing the orbital rim. Both approaches allow a wide angle to access large or complex aneurysms of the anterior circulation from multiple angles. These approaches are also sometimes selected for posterior cerebral artery (PCA), superior cerebellar artery (SCA), and basilar apex aneurysms.[ 2 ] In the senior author’s experience, the zygomatic portion of the classic orbitozygomatic approach is rarely necessary. Instead, the zygoma is drilled, allowing the position of the temporalis muscle to be both inferior and flatter, thus increasing exposure. This is especially advantageous for pre-temporal and transcavernous approaches.

The LSO approach also allows adequate access to anterior circulation and selects high-positioned basilar bifurcation or basilar-SCA aneurysms.[ 16 ] Figure 1 shows an illustrative comparison of the different cranio-orbital craniotomies. Table 1 provides a summary comparison of various cranio-orbital approaches along with the vascular pathologies that they can access, based on anatomical considerations.

Figure 1:

Illustration of bony skull removal for various cranio-orbital approaches.

Table 1:

Comparison of cranio-orbital approaches for vascular pathology, showing favorable and unfavorable variables for common vascular targets.

A summary of a literature review of the use of these approaches for vascular pathology is shown in Table 2 .

Table 2:

Literature review summary: A summary of the current literature discussing the advantages and disadvantages of cranial-orbital approaches for treating vascular pathology.

DISCUSSION

Supraorbital approach: General approach selection and technique considerations

The supraorbital craniotomy is often used as a “keyhole” approach, offering a minimally invasive surrogate with little brain exposure and retraction. It allows a trajectory along the orbital roof for the surgeon to access AcomA, ipsilateral supraclinoid internal carotid artery (ICA), posterior communicating artery (PcomA), anterior choroidal artery (AchA), and proximal, middle cerebral artery (MCA) aneurysms arising near the circle of Willis. The orbital rim limits the superior extension of the trajectory. The supraorbital craniotomy does not allow for an extensive superior trajectory of the operative corridor for distal anterior circulation aneurysms, although this corridor can be enhanced with an orbitotomy. A smaller keyhole approach can limit the approach to fewer angles of attack than a larger craniotomy would afford.[ 22 ] The endoscopic-assisted supraorbital approach can be particularly favorable in illuminating the depth of the field and providing a panoramic view without shadows, rather than changing angles while illuminating with a microscope from a distance.[ 21 ] Risks of the approach can be mitigated with proper planning and understanding of anatomy, but it can include the risk of forehead numbness with damage to the supraorbital nerve, facial weakness from damage to the frontalis branch of the facial nerve, and rhinorrhea if the frontal sinus is traversed and not properly repaired.[ 27 ]

Advantages and disadvantages of surgical targets

Anterior circulation

AcomA

Supraorbital craniotomies can provide an excellent working corridor for AcomA aneurysms, affording more exposure to aneurysms than traditional pterional approaches.[ 6 ] Inferiorly and anteriorly projecting AcomA aneurysms can be favorably approached, while the projection of superiorly directed AcomA aneurysms makes them better suited for approaches such as the interhemispheric or pterional approaches.[ 22 ] Of note, the supraorbital approach requires subfrontal retraction for approaching the AcomA, which puts the olfactory nerve at greater risk compared to the more lateral retraction of the pterional approach.[ 22 ]

ICA, PcomA, and AchA

The subfrontal approach allows medial Sylvian fissure dissection, achieving frontal lobe retraction without temporal lobe retraction that gives visualization of the ICA bifurcation.[ 22 ] Supraclinoidal aneurysms, such as those arising from the PcomA and AChA, are amenable to supraorbital approaches since the field of this surgical corridor centers on the ICA.[ 22 ] Aneurysms requiring drilling of the anterior clinoid process, such as low-lying supraclinoid or paraclinoid ICA aneurysms, require larger craniotomies. Aneurysms originating from the posterior aspect of the ICA are also not amenable to the small angles of the supraorbital craniotomy.[ 22 ]

MCA

To achieve optimal exposure and visualization for MCA aneurysms, the supraorbital craniotomy may be extended laterally several millimeters. Sylvian fissure dissection, as described above, allows access to the aneurysm, although aneurysms distal to the genu are not easily accessed from this approach.[ 22 ]

Posterior circulation

Less commonly, basilar apex aneurysms can be accessed from this approach. It is important to take note of the height of the basilar apex in relation to the anterior skull base. Some authors suggest that basilar apex aneurysms within 1.5 cm of the horizontal line of the anterior skull base are accessible,[ 18 ] while others have suggested a cutoff of 1 cm below the posterior clinoid process.[ 4 ]

Regardless of the aneurysm location, the supraorbital approach is less suited for aneurysms of larger or complex morphology or multiple aneurysms that require multiple angles of clipping compared to larger craniotomies that allow broader angles of approach. In patients where a significantly full brain is expected, or decompression is needed, a larger craniotomy would be more favorable.[ 8 ] Similarly, in the event that a potential bypass graft is needed, a keyhole approach is not ideal.

LSO approach: General approach selection and technique considerations

The LSO craniotomy is employed primarily for anterior circulation lesions as a tailored adaptation of the established pterional craniotomy. It is a simpler version of the pterional approach and utilizes a smaller incision[ 13 ], as seen in Figure 2 .[ 1 ] The cranial opening is smaller than a traditional pterional approach and extends approximately two-thirds above and one-third below the anterior superior temporal line, incorporating the Sylvian fissure at its inferior edge. By performing a smaller craniotomy, the LSO offers the advantage of reduced brain exposure, lower blood loss, better cosmesis, and shorter operative time in comparison to larger craniotomies. The LSO craniotomy allows access to the sellar and suprasellar regions, as well as to the Sylvian fissure. While the LSO does not expose the entire Sylvian fissure, it utilizes the sphenoid ridge as a natural retractor of the temporal lobe, while the surgeon places gentle traction on the frontal lobe to allow stretching of the arachnoid to facilitate visualization and microdissection of the Sylvian fissure.[ 13 ]

Figure 2:

Lateral supraorbital approach. (a) Supraorbital eyebrow, LSO, and pterional incisions. (b) Left LSO exposure. (c) Opticocarotid structures. (d) Oculomotor nerve followed back to the posterior circulation. Courtesy of the Rhoton Collection.[ 1] LSO: Lateral supraorbital. ICA: Internal carotid artery, PCA: Posterior cerebral artery, SCA: Superior cerebellar artery, CN: Cranial nerve, MCA:Middle cerebral artery, ACA: Anterior cerebral artery, PcomA: Posterior communicating artery.

Anterior circulation

With sufficient cerebrospinal fluid (CSF) release and brain relaxation, the LSO approach provides exceptional exposure to reach most anterior circulation lesions – with slight modifications based on specific lesions – to tailor the craniotomy more frontally or laterally. While most anterior circulation lesions may be reached comfortably through the LSO approach, those pathologies pointing posteriorly, such as a large anterior or PcomA aneurysm and giant MCA aneurysms, may prohibit one from using the LSO. In addition, limited exposure to lesions located in the distal anterior cerebral artery territory makes them a less suitable target for this approach.[ 16 ] The more anterior operative corridor reduces exposure to the distal ICA aneurysms compared to the traditional pterional craniotomy, including the PcomA and AchA. MCA aneurysms located superficially in the Sylvian fissure can be accessed with an LSO approach.

Posterior circulation

In experienced hands, high-riding basilar apex aneurysms may be reached with the LSO. The LSO allows access to the basilar tip, but it allows only a narrow corridor and a longer trajectory.[ 7 ]

Cranio-orbital approach (“Inside-out”): General approach selection and technique considerations

Cranio-orbital craniotomies involve accessing the intraorbital compartment from within the cranial space, as opposed to the orbital-cranial approach, which accesses the intracranial compartment from the outside using the orbital corridor.[ 2 ] The cranio-orbital approach allows excellent exposure, versatility, and optimal angles of approach. It is a complex surgical procedure that may require extensive training and experience to perform safely and effectively. The orbital roof and lateral wall of the orbit are removed, leaving the orbital rim in place, as seen in Figure 3 .[ 1 ] This approach carries a risk of orbital injury: when removing parts of the orbital wall, there is a risk of injuring the optic nerve or other orbital structures, potentially resulting in visual deficits or other complications. The pterional incision begins at the zygomatic arch and curves antero-medially toward the midline or just beyond the midline at the hairline. While effective, its larger incision and potential disruption of the temporalis muscle may result in depressions in the sphenoid region, making the cosmesis of this approach less desirable.

Figure 3:

Cranio-orbital approach (“Inside-Out”). (a) Right modified one-piece craniotomy. McCarty keyhole accesses the frontal dura and periorbita. (b) Sylvian fissure exposure. (c) Exposure of anterior circulation. (d) Exposure of posterior circulation. Courtesy of the Rhoton Collection.[ 1] ICA: Internal carotid artery, PCA: Posterior cerebral artery, SCA: Superior cerebellar artery, CN: Cranial nerve, MCA:Middle cerebral artery, ACA: Anterior cerebral artery.

Advantages and disadvantages of surgical targets

Anterior circulation

Exposure of anterior circulation lesions is maximized with a cranio-orbital approach. It allows direct access to the orbital apex, sphenoid ridge, and adjacent structures, making it suitable for a wide range of aneurysm locations in this region. It enables surgeons to attack from several angles, facilitating safe aneurysm clipping. It can be adapted and modified to access different types of aneurysms, including those in the anterior and posterior circulation.

Posterior circulation

To access superiorly situated lesions, such as high-riding basilar apex aneurysms or vascular malformations in this region, additional orbital removal may be required. This can be done as a separate two-piece osteotomy after performing a standard pterional craniotomy.[ 9 ] The procedure involves skeletonizing the posterior orbital wall around the sphenoid wing, making cuts along the frontozygomatic process, and typically positioning them laterally to the supraorbital nerve to avoid entering the frontal sinus. The orbital bar can be pre-plated for cosmetic optimization before fracturing it. Alternatively, the orbital roof can be removed using a one-piece technique, similar to the cranioorbito-zygomatic approach.[ 20 ] However, the one-piece technique necessitates the removal of more of the posterior orbital wall after the elevation of the cranio-orbital flap and results in significantly less total orbitotomy compared to the two-piece method.[ 28 ] In addition, for deeper aneurysms at the basilar apex, it can be helpful to remove the posterior orbital wall to facilitate extradural exposure for anterior clinoidectomy by clearly delineating the three attachments of the anterior clinoid process to the skull base (1-optic canal roof, 2-medial sphenoid wing, and 3-optic strut).

In summary, the cranio-orbital approach offers excellent exposure and versatility for treating intracranial aneurysms, but it comes with potential cosmetic concerns, complexity, and risk of injury to orbital structures. Surgeons should carefully consider these factors when determining the most appropriate approach for each patient’s specific case.

Orbital-pterional approach (“Outside-in”): General approach selection and technique considerations

The cranio-orbital approach [ Figure 4 ][ 1 ] is considered an “inside-out” approach to access the orbit from the intracranial space. Conversely, orbito-cranial approaches are an “outside-in” approach to accessing the intracranial space from the orbit.[ 2 ] Its corridor to the anterior, middle, and interpeduncular fossae allows access to all anterior circulation, as well as SCA and basilar apex aneurysms.[ 5 , 27 ] It has great versatility in approaching a wide array of aneurysms. The removal of the superolateral orbital rim allows increased exposure for targets along the posterior clinoid process, tentorium, and basilar tip.[ 25 ]

Figure 4:

Orbito-pterional approach (“Outside-In”). (a) Left pterional craniotomy. (b) Sylvian fissure. (c) Sylvian fissure dissection exposes the MCA. (d) The pretemporal approach, retracting the temporal pole backward, exposes the middle fossa dura, cavernous sinus, and posterior circulation. Courtesy of the Rhoton Collection.[ 1] MCA: Middle cerebral artery. ICA: Internal carotid artery, PCA: Posterior cerebral artery, SCA: Superior cerebellar artery, CN: Cranial nerve, ACA: Anterior cerebral artery.

Advantages and disadvantages of approach for surgical targets

Anterior circulation

AcomA

The orbito-pterional craniotomy is an excellent working channel for accessing AcomA aneurysms. It obviates the need for splitting the Sylvian fissure and necessitates minimal brain retraction when accessing these aneurysms.[ 3 ] When using this approach to access anteriorly projecting AcomA aneurysms, it may prove difficult to access the lamina terminalis for brain relaxation; therefore, the Liliequist membrane should be accessed for CSF release from the prepontine cistern. In a study comparing the orbito-pterional and traditional pterional approaches for AcomA aneurysm clipping, Andaluz et al. found that the orbito-pterional craniotomy improved angles of observation, with the infrequent need for gyrus rectus resection or parenchymal damage from retraction.[ 3 ] This improvement is accomplished by allowing a more basal approach, particularly for AcomA aneurysms projecting superiorly and posteriorly into the interhemispheric fissure.[ 5 ] Adding the posterolateral orbitotomy to the traditional pterional craniotomy also widens the angle for accessing the ICA bifurcation, suprasellar region, and particularly the AcomA complex.

Posterior circulation

The orbito-pterional approach permits access to the interpeduncular cistern, allowing access to the SCA and basilar apex aneurysms. Tayebi et al. found that the orbito-pterional approach offered improved PCA exposure and visualization of perforators, as well as an improved area of exposure to facilitate safe clipping of basilar apex aneurysms compared to a pterional approach.[ 29 ] The superolateral orbitotomy affords an improved superior trajectory to high-riding basilar apex aneurysms. The more invasive orbitozygomatic approach did not provide any further significant exposure to the basilar apex when compared to the orbito-pterional approach.[ 29 ]

Trans-cavernous approach: General approach selection and technique considerations

The cavernous sinus is often considered a formidable operative target or approach pathway. Although endovascular treatment modalities are commonly employed for vascular pathology in this region, this approach is still considered a viable operative corridor, particularly to posterior circulation pathology not otherwise amenable to endovascular treatment.[ 23 ] A pterional craniotomy is made with widened exposure to allow pretemporal access by ensuring the craniotomy extends to the level of the floor of the middle fossa and flush with the orbital roof. Next, a pretemporal peeling is performed to elevate the temporal lobe dura from the dura propria off the lateral wall of the cavernous sinus with the Hakuba and Dolenc techniques.[ 12 , 15 ] The middle meningeal artery is divided as it enters the foramen spinosum, and the three branches of the trigeminal nerve are identified [ Figure 5 ].[ 1 ] An extradural anterior clinoidectomy is also performed to allow access and visualization of the clinoidal and ophthalmic segments of the ICA. This step also allows better visualization of the posterior clinoid process, which may need to be removed to improve visualization of the basilar trunk for proximal control.

Figure 5:

Transcavernous approach. (a) Cavernous sinus exposure. (b) Exposure of cranial nerves, posterior fossa, ICA after anterior clinoidectomy and anterior petrosectomy. (c) Posterior clinoid between oculomotor nerve and ICA. (d) BA exposure after posterior clinoidectomy. Courtesy of the Rhoton Collection.[ 1] ICA: Internal carotid artery. , PCA: Posterior cerebral artery, SCA: Superior cerebellar artery, CN: Cranial nerve, MMA:Middle meningeal artery, GSPN: Greater superficial petrosal nerve, BA: Basilar artery.

Advantages and disadvantages of surgical targets

Anterior circulation

When accessing paraclinoidal aneurysms with this approach, incising the falciform ligament allows for the safer mobilization of the optic nerve. The dural ring is cut proximal to the takeoff of the ophthalmic artery to allow exposure to the aneurysm. At other times, the cavernous segment of the ICA must be accessed for proximal control. When this becomes necessary, such as when an aneurysm is abutting the clinoid process, access to the cavernous carotid can be accessed through Parkinson’s triangle.[ 23 ]

Posterior circulation

When a high-riding basilar apex aneurysm is being approached, access for proximal control requires mobilization of the oculomotor nerve, which is in the center of the operative field in this route to the basilar apex. It may also become necessary to divide the PcomA for unimpeded access to the interpeduncular fossa. In the case of low-lying basilar apex aneurysms, a circumferential view of the aneurysm for safe access and treatment can be achieved by performing a posterior clinoidectomy to expose the SCA and contralateral PCA to obtain proximal control.[ 23 ] The transcavernous approach can also be used for SCA aneurysms. After anterior clinoidectomy, the Sylvian fissure is split, and the distal dural ring is incised. A subpial resection of the uncus, as well as posterior clinoidectomy, can allow the widening of the oculomotor and tentorial windows if necessary. The roof of the cavernous sinus can be opened over the oculomotor nerve utilizing the Dolenc technique, and the oculomotor nerve is visualized from its origin in the interpeduncular fossa adjacent to the SCA all the way to its entry into the cavernous sinus. This maneuver allows for safer mobilization of the nerve while avoiding injury to it.[ 19 ]

Case examples

Case 1

A 60-year-old female presented with a Hunt-Hess 2, Fisher 2 subarachnoid hemorrhage secondary to a ruptured PcomA aneurysm [ Figure 6 ]. The patient underwent a cranio-orbital craniotomy, Hakuba “peeling” of the temporal dura propria from the lateral wall of the cavernous sinus, and extradural anterior clinoidectomy [ Figures 7 and 8 ]. The clinoidal segment of the ICA was secured extradurally for proximal control before dural opening along the Sylvian fissure. The proximal Sylvian fissure was split, and the distal dural ring was dissected. The aneurysm was initially clipped and further explored, with an intraoperative rupture controlled through trapping of the aneurysm with proximal control obtained extradurally in the clinoidal segment of the ICA [ Figure 9 ]. Final clipping was performed, and trapping clips were removed [ Figures 10 and 11 ]. Postoperative imaging showed complete obliteration of the aneurysm, and the patient remained at a neurological baseline [ Figures 12 and 13 ].

Figure 6:

Preoperative angiogram shows a wide necked, ruptured posterior communicating artery aneurysm (red arrow).

Figure 7:

Intraoperative view of extradural corridor following cranio-orbital craniotomy removing orbit roof.

Figure 8:

Intraoperative view after removal of anterior clinoidal process, with access to the clinoidal ICA for proximal control. ICA: Internal carotid artery.

Figure 9:

Intraoperative view of (a) intraoperative rupture of the posterior communicating artery aneurysm during inspection of the aneurysm after the pilot clip was placed (b) and with proximal control obtained with temporary clipping of the clinoidal ICA. ICA: Internal carotid artery.

Figure 10:

Intraoperative view of trapping clips in place.

Figure 11:

Intraoperative view of final clipping of the aneurysm.

Figure 12:

(a) Postoperative CT head can be seen here demonstrating the bony work that was performed. (b) The right orbital roof and anterior clinoidal process (yellow hashes) are noted to have been drilled away. CT: Computed tomography.

Figure 13:

Postoperative angiogram shows obliteration of the aneurysm.

Case 2

A 42-year-old male presented with acute severe headache, sudden left hemiplegia, and right oculomotor nerve palsy. Magnetic resonance imaging demonstrated a completed right SCA stroke. Computed tomography angiogram and formal angiography confirmed an unruptured large partially thrombosed right SCA aneurysm with mass effect occluding the right SCA, which was thought to be filling and growing [ Figure 14 ]. Endovascular treatment was deemed unfavorable due to a recent thrombo-embolic stroke and the wide neck of the aneurysm; bypass was not chosen due to a completed stroke.

Figure 14:

Preoperative angiography showing large right thrombosed SCA aneurysm and no filling of the occluded right SCA. SCA: Superior cerebellar artery. *No filling of occluded R SCA.

The patient underwent an orbito-pterional craniotomy, Hakuba “peeling” of the temporal dura propria from the lateral wall of the cavernous sinus, and anterior clinoidectomy [ Figure 15 ]. The oculomotor and trochlear nerves were exposed, and the tentorial edge was cut between them to widen the oculomotor-tentorial window. A posterior clinoidectomy was performed with an ultrasonic bone claw. The SCA and PCA were identified, and the aneurysm was clipped [ Figures 16 and 17 ]. Follow-up imaging showed aneurysm obliteration, with postoperative resolution of preoperative oculomotor nerve palsy [ Figure 18 ].

Figure 15:

Intraoperative view of the extradural corridor provided by the orbito-pterional craniotomy. The optic strut is being drilled for anterior clinoidectomy here.

Figure 16:

Intraoperative view of clipped SCA aneurysm, showing the aneurysm dome’s mass effect on the oculomotor nerve (CN3) and preservation of the PCA. SCA: Superior cerebellar artery, PCA: Posterior cerebral artery.

Figure 17:

Intraoperative indocyanine green shows patent basilar apex and PCAi and no flow in the SCA aneurysm. SCA: Superior cerebellar artery, PCAi: Ipsilateral posterior cerebral artery. ICA: Internal carotid artery.

Figure 18:

Postoperative CT angiogram with clip ligation of the aneurysm and bony work of partial anterior clinoidectomy (due to the middle clinoid process encircling the ICA) and posterior clinoidectomy can be visualized. CT: Computed tomography, ICA: Internal carotid artery. PCA: Posterior cerebral artery, SCA: Superior cerebellar artery.

Case 3

A 30-year-old female presented with a large unruptured left A1– A2 junction AcomA aneurysm with anterior inferior projection beneath and adherent to the left optic nerve. On examination, the patient is neurologically intact with no focal neurological deficits. The aneurysm was observed to have increased in size over a 2-month interval between initial and repeat angiography. Preoperative angiography is shown in Figure 19 .

Figure 19:

Preoperative angiography.

Initial attempts for endovascular treatment were made and aborted due to unfavorable anatomy. The patient underwent left LSO craniotomy with orbital roof osteotomy for clip ligation of the aneurysm [ Figures 20 and 21 ]. This approach allowed a good corridor of access and visualization for this anteriorly projecting anterior circulation aneurysm.

Figure 20:

Intraoperative view of clipped AcomA aneurysm, showing the dome’s anterior projection into the retracted gyrus rectus. ONi was completely underneath the aneurysm. AcomA: Anterior communicating artery, ONi: Ipsilateral optic nerve.

Figure 21:

Postoperative CT angiogram showing successful clip ligation of the aneurysm. CT: Computed tomography.

Case 4

A 46-year-old female had previously presented to the hospital with headaches, incidental partially thrombosed left PCA fusiform aneurysm, and basilar apex aneurysm with no significant right P1 [ Figure 22 ]. Lumbar puncture did not indicate rupture. Endovascular therapy for these aneurysms was not felt to be a good option, and the patient elected to undergo clipping of the aneurysms. Left orbital-pterional craniotomy with a trans-cavernous approach was performed for clipping the right basilar apex aneurysm. The transcavernous approach allowed visualization around the neck of the aneurysm for safe clip ligation [ Figures 23 and 24 ]. The left PCA fusiform aneurysm was then clipped through a subtemporal approach [ Figures 25 and 26 ].

Figure 22:

Preoperative angiogram showing left fusiform posterior communicating artery aneurysm (red arrow) and basilar apex aneurysm (black arrow).

Figure 23:

(a) Intraoperative view of V1, V2, and V3 and MC. Meckel’s cave was opened sharply for CSF release. (b) The opening in Meckel’s cave for CSF release is shown. MC: Meckel’s cave, CSF: Cerebrospinal fluid.

Figure 24:

Intraoperative view of the transcavernous approach through the ON-carotid (ICA) corridor. SCAi and PCAc are seen. ON: Optic nerve, SCAi: Ipsilateral superior cerebellar artery, PCAc: Contralateral posterior cerebral artery, ICA: Internal carotid artery. CN: Cranial nerve.

Figure 25:

Aneurysm viewed through the transcavernous approach. Proximal control of the basilar artery was performed with temporary clipping utilizing the oculomotor triangle, but the angle of attack for clip ligation of the aneurysm was more optimal through the optic-carotid triangle. Lip ligation of the aneurysm was more optimal through the optic-carotid triangle.

Figure 26:

Postoperative CT angiogram showing successful clip ligation of the basilar and PCA aneurysms. PCA: Posterior cerebral artery.

CONCLUSION

Supraorbital, LSO, cranio-orbital (“outside-in”), and orbital-pterional (“inside-out”) craniotomies are approach modifications of the traditional pterional craniotomy. These different variations are useful for treating various vascular pathologies of the anterior and posterior circulation. The half-and-half or transcavernous approaches can be useful additions to these approaches. Understanding the advantages and disadvantages of each is important in optimal approach selection.

Ethical approval:

The Institutional Review Board approval is not required.

Declaration of patient consent:

Patient’s consent was not required as there are no patients in this study.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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