The Eyelid Trans-orbital Trans-cavernous Approach to the Basilar Apex: A Cadaveric Proof-of-Concept Study

Abstract

Objective The pretemporal transcavernous approach is an elegant technique that provides exposure to the basilar apex, which is conventionally completed with a frontotemporal incision. This can also be performed via a minimally invasive eyelid transorbital approach, which has unique attributes. This is a proof-of-concept cadaveric study to demonstrate details of the combination of these two approaches. Design This study is a proof-of-concept study using cadaveric heads. Setting This study is a proof-of-concept study in a cadaveric laboratory. Participants A latex-injected cadaveric head. Main Outcome Measures Detailed dissection was performed and demonstrated in a step-by-step fashion. Results The eyelid transorbital approach provides the exact exposure required to complete the pretemporal osteotomy including an anterior clinoidectomy and dissection, so that a transcavernous approach can be completed. The basilar apex and its branches can also be accessed via the eyelid transorbital approach, with comparable exposure to the traditional approach; however, the access trajectory is much narrower. It takes advantages of the inferior corridor with a more medial access angle and provides a complementary perspective to the cavernous sinus contents and basilar apex complex. Conclusion The combination of an eyelid transorbital and pretemporal transcavernous approaches can achieve a deep exposure via a minimally invasive incision, which may add an additional approach to the cavernous sinus and basilar apex regions.

Keywords: basilar apex; pretemporal approach; transcavernous approach; transorbital approach.

Fig. 1

A step-by-step dissection of the eyelid transorbital pretemporal transcavernous approach. ( A ) The cadaveric head was positioned supine with approximate 20 degrees extension and contralateral rotation, an eyelid incision was planned from medial one-third eyelid to lateral canthus with a horizontal extension on the right side. ( B ) The skin was incised and a dissection plane superficial to the continuum of the orbital septum and periosteum was developed; the periosteum incision was made along the orbital rim, to avoid entering the periorbita. A horizontal relaxing cut to the temporalis fascia was made. ( C ) A subperiosteal dissection was carried out inferiorly that the inferior orbital rim (black arrow) and root of zygoma (white arrow) were exposed. ( D ) The craniotomy and orbitotomy were completed in one piece. The MacCarty keyhole was placed to expose both the orbit (green arrow) and the anterior fossa (red arrow). The black dashed line represents the cut from the keyhole down on the lateral orbital wall. This was finalized by disconnecting the orbital roof with a chisel. ( E ) The periorbita and frontal dura were exposed after the initial craniotomy. ( F ) Further removal of the lateral orbital wall unveiled the superior orbital fissure and bulk of the greater sphenoid wing. ( G ) The superior orbital fissure and meningo-orbital band were then exposed after removing the greater sphenoid wing. Pretemporal dissection can easily permit access to the maxillary strut and foramen rotundum. ( H ) The anterior clinoid process was demonstrated after the meningo-orbital band was incised. The optic nerve and optic canal were exposed from the orbital side. ( I ) The anterior clinoidectomy was then completed that the clinoid carotid artery, remaining optic strut, and optic nerve were exposed. ( J ) The pretemporal extradural dissection exposes the lateral wall of the cavernous sinus structures including the oculomotor nerve (CN III), trochlear nerve (CN IV), ophthalmic nerve (V1), and maxillary nerve (V2). The pterygopalatine fossa can be entered as continuation of foramen rotundum. Endoscopic view of the lateral wall ( K ) and the roof ( L ) of the cavernous sinus. The dura was opened along the Sylvian fissure microscopic ( M ) and endoscopic ( N ) views demonstrated the neurovascular structures were connected intradurally and extradurally. The posterior clinoid process was obscuring the view to the posterior fossa via the carotid–oculomotor triangle. The full length of the oculomotor nerve (green arrow heads) was dissected from the midbrain to superior orbital fissure. A posterior clinoidectomy was completed; microscopic view ( O ) and endoscopic view ( P ) demonstrated direct access to the basilar apex and basilar artery branches. The full length of the oculomotor nerve was again demonstrated (black dashed line). Closer inspection ( Q ) showed optimal deep exposure of the basilar artery, bilateral superior cerebellar arteries (SCAs), and posterior cerebral arteries (PCAs). ( R ) Endoscopic view of the cavernous sinus from an anterior perspective that was offered by the eyelid transorbital approach. ( S ) The full length of the cavernous segment carotid artery from the foramen lacerum to proximal dural ring was demonstrated. The abducens nerve was shown immediately lateral to the carotid artery; the inferolateral trunk was also demonstrated supplying the middle fossa foramens. ( T ) A zoomed-out endoscopic view of the cavernous sinus from the antero-lateral perspective included all cavernous sinus contents. Ant., anterior; BA, basilar artery; Clin., clinoid; CN II, optic nerve; CN III, oculomotor nerve; CN IV, trochlear nerve; CN VI, abducens nerve; Cont., contralateral; For., foramen; Front., frontal; Gr., greater; ICA, internal carotid artery; Ipsi., ipsilateral; Lat., lateral; Max., maxillary; N., nerve; Orb., orbital; PCA, posterior cerebral artery; Pcom. A, posterior communicating artery; Post., posterior; Pro., process; Sup., superior; SCA, superior cerebellar artery; V1, ophthalmic nerve; V2, maxillary nerve.

Fig. 2

Artistic illustration demonstrating the trajectory of the eyelid approach to the basilar apex. Copyright of Lindsay Heisler.

Fig. 3

Comparison of the eyelid transorbital and traditional pretemporal transcavernous approach on a skull model; ( A ) a coronal view demonstrates the eyelid approach provides more inferior exposure and a more superior access angle; ( B ) an axial view demonstrates the eyelid approach permits a more medial access angle which is aligned closer to midline, with the potential to offer a more anatomically oriented exposure to the basilar apex complex.

Fig. 4

Comparison of the viewing angle of the eyelid transorbital and traditional pretemporal transcavernous approach to the basilar apex (right-sided approaches). ( A ) The eyelid approach provides a more antero-posteriorly oriented corridor that is parallel to the course of the oculomotor nerve. The basilar apex branches were accessed more anatomically oriented from the trajectory. The yellow arrow represents the traditional transcavernous approach trajectory, which is more medio-laterally oriented. ( B ) The traditional approach provides access to the basilar apex at a lateral angle; this trajectory can be more challenging to access the contralateral neck, but visualization of the basilar artery perforators can be more straightforward given the access angle. The contralateral PCA was visualized with gentle retraction. The green arrow represents the eyelid transorbital approach trajectory, which is more antero-posteriorly oriented. BA, basilar artery; Cont., contralateral; Ipsi., ipsilateral; PCA, posterior cerebral artery; SCA, superior cerebellar artery.