The OZ Chapter: Original OZ, Modified for Parietal, Modified for Frontal, Cosmetic Results of the OZ

Historical Aspects

The “workhorse of skull base neurosurgery,” the orbitozygomatic approach (OZA) is a highly versatile surgical technique that provides access to lesions involving the orbital apex, cavernous sinus, anterior and middle fossa floor, and posterior fossa cisterns, and minimizes the need for fixed brain retraction. The earliest elements of the OZA can be found in the description of surgical approaches to the pituitary by McArthur and Frazier in the early 1900s, and since then the OZA has evolved in complexity, modification, and application. ^,

Yasargil described additional elements of the OZA as essentially an expansion of the class pterional craniotomy, which includes the removal of the sphenoid wing and clinoid process as well as further description of orbital osteotomies including the lateral osteotomy. Later, Jane et al. further expanded upon orbital osteotomy techniques and variations.

The modern OZA was first described by Pellerin et al. in 1986 and Hakuba et al. in 1984. ^, The Pellerin et al. case series described a fronto-orbital one-piece craniotomy with removal of the greater sphenoid wing for sphenoid wing meningiomas. Hakuba et al. reported a similar craniotomy approach, which they called OZA for parasellar tumors and cavernous sinus lesions. Al-Mefty et al. and Pieper et al. then combined these techniques and established its use in the treatment of skull base lesions.

Since its initial description, several modifications have been made to the conventional OZA, notably including performing the craniotomy in several pieces rather than in one piece as well as changes to the location and types of cuts in the removal of the bony components. Using a variety of different working angles, the OZA is now used in the treatment of a range of pathologies and locations including in the brainstem, cavernous sinus, orbit, and infra- and subtemporal regions.

Indications

The orbitozygomatic (OZ) craniotomy is considered an extension of the classic pterional approach that allows the surgeon to access the anterior and middle cranial fossae with greater visualization of the basal structures and minimal brain retraction. This approach allows access through transsylvian, subfrontal, or subtemporal corridors. The primary indication for the OZA approach is for lesions located in the infratemporal fossa, orbit, cavernous sinus, interpeduncular cistern, rostral brainstem, and petroclival region. For each of these locations, slight modifications to the conventional OZA might be required to ensure maximal visualization. For orbital lesions, a lateral orbital osteotomy provides maximal exposure of the orbital contents and the greater wing of the sphenoid. Importantly, for orbital lesions, a burr hole should be placed at the McCarty’s keyhole exposing the frontal supraorbital dura, the orbital roof, and periorbita. ^{, , ,} This strategically placed burr hole provides visualization of the optic apparatus and the entrance of the optic nerve. ^{, , ,} Next for petroclival and sphenoid sinus lesions, especially those that involve multiple components of the bony framework of this region, inferior retraction of the temporalis muscle should be used for exposure. ^{, , , , ,} Finally the OZA can be used when an inferior-to-superior surgical corridor is needed for anterior diencephalic or brainstem lesions.

An OZA may be indicated for neurovascular lesions such as brain arteriovenous malformations and cavernous malformations involving basal forebrain structures, diencephalon, and rostral brainstem, and brain aneurysms involving the internal carotid artery proximal to the distal dural ring or low-riding basilar artery bifurcation. However this approach is not restricted to only these locations. The OZA is also indicated for large and complex vascular lesions, specifically lesions that a more restricted approach might increase the difficulty to clip. ^{, ,} For ruptured basilar artery aneurysms, a conventional OZA can be combined with a transsylvian approach. When combined, the surgeon is given improved visualization of the surgical corridor and, importantly, better access to the Circle of Willis.

In conclusion, when performed appropriately, the OZA provides improved access and minimized brain retraction. Specifically, due to the increased removal of zygoma and orbit, OZA gives increased access to the anterior cranial fossa, cavernous sinus, and intrinsic brainstem lesions and vascular lesions of the posterior circulation. Additionally, OZA can minimize brain retraction through increased working angles and visualization of important structures. Finally, compared to other approaches on similar lesions, OZA allows the reconstruction of the bony components and preservation of the blood supply. ^,

Contraindications

The main contraindication for the OZA is medially located lesions requiring midline visualization; specifically, this would include retrochiasmatic craniopharyngiomas. As with the treatment of all lesions, when deciding if the patient will be able to tolerate the approach, considerations need to be given to lesion size, location, and pathology. In all cases, choice of OZA demands a multidisciplinary approach with careful evaluation of risks and benefits.

Technique