Transorbital approach to the cavernous sinus: an anatomical study of the related cranial nerves

Abstract

Background: The cavernous sinus (CS) is a demanding surgical territory, given its deep location and the involvement of multiple neurovascular structures. Subjected to recurrent discussion on the optimal surgical access, the endoscopic transorbital approach has been recently proposed as a feasible route for selected lesions in the lateral CS. Still, for this technique to safely evolve and consolidate, a comprehensive anatomical description of involved cranial nerves, dural ligaments, and arterial relations is needed.

Objective: Detailed anatomical description of the CS, the course of III, IV, VI, and V cranial nerves, and C3-C7 segments of the carotid artery, all described from the ventrolateral endoscopic transorbital perspective.

Methods: Five embalmed human cadaveric heads (10 sides) were dissected. An endoscopic transorbital approach with lateral orbital rim removal, anterior clinoidectomy, and petrosectomy was performed. The course of the upper cranial nerves was followed from their apparent origin in the brainstem, through the middle fossa or cavernous sinus, and up to their entrance to the orbit. Neuronavigation was used to follow the course of the nerves and to measure their length of surgical exposure.

Results: The transorbital approach allowed us to visualize the lateral wall of the CS, with cranial nerves III, IV, V1-3, and VI. Anterior clinoidectomy and opening of the frontal dura and the oculomotor triangle revealed the complete course of the III nerve, an average of 37 (±2) mm in length. Opening the trigeminal pore and cutting the tentorium permitted to follow the IV nerve from its course around the cerebral peduncle up to the orbit, an average of 54 (±4) mm. Opening the infratrochlear triangle revealed the VI nerve intracavernously and under Gruber's ligament, and the extended petrosectomy allowed us to see its cisternal portion (27 ± 6 mm). The trigeminal root was completely visible and so were its three branches (46 ± 2, 34 ± 3, and 31 ± 1 mm, respectively).

Conclusion: Comprehensive anatomic knowledge and extensive surgical expertise are required when addressing the CS. The transorbital corridor exposes most of the cisternal and the complete cavernous course of involved cranial nerves. This anatomical article helps understanding relations of neural, vascular, and dural structures involved in the CS approach, essential to culminating the learning process of transorbital surgery.

Keywords: cavernous sinus; cranial nerve; endoscopic; interdural peeling; superior eyelid; transorbital.

Figure 1

Lateral wall of the cavernous sinus and third cranial nerve exposed from the transorbital perspective (Cadaveric dissection, left orbit). (A) The interdural peeling unveils the lateral wall of the cavernous sinus (CS). A thin dural layer allows to observe the cranial nerves coursing in the lateral wall. Opening of the dura of the frontal lobe and opening the infratrochlear triangle allows to visualize the cavernous, clinoidal, ophthalmic, and communicating segments of the internal carotid artery (ICA). ON, Optic Nerve. (B) After the anterior clinoidectomy, the III cranial nerve is seen lateral and underneath the clinoidal segment of the ICA. (C) In the roof of the CS, the oculomotor triangle is opened, so that (D) the course of the III cranial nerve is fully seen. (E,F) The III nerve is followed in the posterior fossa towards the interpeduncular cistern. The basilar artery and the posterior cerebral artery are shown in relation to the III nerve.

Figure 2

Fourth cranial nerve exposed from the transorbital perspective (Cadaveric dissection, left orbit). (A,B) The IV cranial nerve is exposed in the lateral wall of the cavernous sinus (CS), right beneath the III nerve. (C,D) The IV nerve is followed from the CS towards the posterior fossa, by opening the oculomotor triangle. (E,F) The IV nerve is shown in its cisternal segment, as it courses around the cerebellar peduncle. The apparent origin is not visible from the transorbital perspective.

Figure 3

Sixth cranial nerve exposed from the transorbital perspective (Cadaveric dissection, left orbit). (A,B) The extended anterior petrosectomy, achieved after removal of the lateral orbital rim, reveals the VI cranial nerve in the posterior fossa. (C) The extended petrosectomy allows to visualize the retroclival area from the transorbital view. The contralateral VI nerve is seen, entering Dorello’s canal. Additionally, the V contralateral cranial nerve is seen entering the trigeminal pore, and so it is the contralateral III nerve entering the oculomotor triangle. (D) In the middle fossa, Mullan’s triangle is opened. (E) Opening Mullan’s triangle reveals the cavernous segment of the internal carotid artery (ICA) with the sympathetic plexus. The IV nerve is seen in intimal relation to the ICA. (F) The IV nerve can be followed intracavernously until its entrance through Dorello’s canal.

Figure 4

Fifth cranial nerve exposed from the transorbital perspective (Cadaveric dissection, left orbit). (A) The interdural peeling of the cavernous sinus, and extradural peeling of the middle cranial fossa (MCF) floor reveal the tree branches of the trigeminal nerve (V1, V2, V3). (B) Opening the dura in Meckel’s cave reveals the fibers of the trigeminal root. (C) Opening the trigeminal pore allows to follow the V nerve towards its course at the posterior fossa. (D) The trigeminal root is seen at its apparent origin in the ventrolateral pons. SCA, Superior Cerebellar Artery.

Figure 5

Three-dimensional reconstructions of the trajectories of the cranial nerves related to the cavernous sinus (Cadaveric specimens, Brainlab). (A) Superior view. The course of the cranial nerves related to the cavernous sinus has been plotted in the magnetic resonance imaging and computed tomography scans, according to the points obtained with the neuro-navigation system during the transorbital dissections. (B) The length of the course of each cranial nerve (cn) is shown.