Transorbital Microscopic Surgery: The Most Minimally Invasive Corridor to Many Intracranial Structures

Introduction: Transorbital neuroendoscopic surgery offers a new level of minimally invasive, minimally disfiguring skull base surgery with maximal surgical visualization. The idea of endoscopic orbital access aimed to achieve equal visibility, surpass the anatomical limitations of the endonasal approach, and decrease the overall invasiveness and complications associated with open skull base surgery. However there are limitations to the endoscope's capabilities. Crowding of an already small surgical corridor, as well as two-dimensional viewing restricts the benefits of this access portal. Feasibility studies on use of the microscope for a transorbital approach have yet to be established.

Methods: A total of six cadaveric dissections were completed. The microscopic transorbital approach to the anterior cranial fossa and paramedian structures were systematically completed using a Zeiss Pentero operating microscope. All dissection steps and utilized instrumentation was recorded to ensure approach methodology homogeneity. We established the anatomical parameters of the transorbital microsurgical craniectomy, as well as highlighted the visible and accessible neuroanatomy via this access corridor. The average size of the orbital roof craniectomy was measured.

Results: Incision and periorbital dissection. Following identification of the supraorbital notch, a 4.5-cm superior lid crease incision is made. Orbital rim exposure and preseptal dissection are imperative. The periosteum is incised to allow for subperiosteal dissection. The frontozygomatic suture represents the most lateral boundary and the division of the anterior and middle cranial fossae. The periorbita is swept superolaterally, then superomedially to the level of the anterior and posterior ethmoidal arteries. Deep dissection along the medial wall leads to the optic nerve as it exits the optic canal. At the superolateral apex of the supraorbital fissure lies the frontosphenoidal suture ([Fig. 1]).

Orbital roof craniectomy. The orbital roof craniectomy is defined as follows:

• Lateral boundary: frontozygomatic suture to the frontosphenoidal suture.

• Medial boundary: frontal sinus and cribriform plate.

• Anterior boundary: frontal sinus and orbital rim.

Craniectomy size. The average size of the craniectomy produced was 440 mm² with a range of 337.07–572.34 mm².

Intracranial dissection. The ipsilateral optic nerve and internal carotid artery are fully exposed and no frontal lobe retraction required for identification of the A1/M1 bifurcation ([Fig. 2]). The complete length of the ipsilateral A1 is visible and accessible. Minimal manipulation of the frontal and temporal lobes is necessary to produce impressive visualization of the M1 artery as it traverses the sylvian fissure. Although the anterior communicating artery is evident, visualization and instrument maneuverability is obstructed by the lateral orbital rim, inhibiting potential operative ability.

Conclusion: Transorbital microsurgery (TMS) is a feasible surgical corridor for intracranial access. Mobilization of the orbital contents is imperative for maximal intracranial access and protection of the globe. Frontal lobe base, ipsilateral optic nerve, and the majority of the ipsilateral anterior circulation, including the M1 segment with splitting of the fissure are all accessible. The orbital rim acts as the superior and lateral boundary to instrument freedom and impairs midline visualization. This cosmetically satisfactory approach causes minimal destruction of the anterior skull base with maximal anterior cranial fossa floor exposure without sinus invasion.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
12 February 2021