13 Lateral Orbitotomy Approach to the Orbit and Cavernous Sinus
Gmaan A. Alzhrani and William T. Couldwell
Abstract
The transcranial approach is a viable route to reach several lesions in the orbital cavity, and the perfect route to follow lesions with superior invasion to the orbit or optic canal. In this chapter, we describe the transcranial approach to the orbit, its indications, limitations, and possible complications.
Keywords: Keywords: orbital tumors, cavernous sinus, orbital decompression, lateral approach
13.1 Historical Background
The first description of the lateral orbitotomy approach (LOA) was published by Kronlein in 1889 to describe the removal of an orbital dermoid using a curvilinear incision with the convexity of the curve located at the region of the lateral orbital rim.1 Since then, the LOA has undergone many modifications to enable access to intraorbital, cavernous sinus, and middle fossa lesions. These modifications are related to the skin incision and the extent of bony removal. In 1953, Berke2 used a straight skin incision extending from the lateral canthus to a distance of 35 to 40 mm along the zygomatic bone toward the external auditory meatus for treatment of 25 cases of different retrobulbar lesions. Stallard3 , 4 popularized a skin incision that extends from the lateral end of the eyebrow along the lateral orbital rim and then curves posteriorly parallel to the zygomatic arch for treatment of malignant exophthalmus. In 1999, Harris and Logani5 proposed the “eyelid incision” that extends along the upper eyelid crease below the eyebrow, curves lateral to the lateral canthus, and ends shortly past the orbital rim along the zygomatic arch; they described its use for treatment of 600 patients with orbital tumors. This incision is the most widely used incision nowadays for LOA because it offers better cosmetic results.6
After the introduction of microsurgical techniques in neurosurgery in the 1960s, Maroon and Kennerdell7 published the first report describing the use of microsurgical techniques to remove lesions superior, lateral, and inferior to the optic nerve through an LOA in 1976. In subsequent years, many authors reported modifications related to the extent of bone removal to access intracranial and intraorbital lesions. Andaluz et al8 extended the LOA to incorporate the superior orbital rim and a small supraorbital craniotomy through a supratarsal skin incision for treatment of frontal cranial base and suprasellar lesions, and anterior circulation aneurysms. Altay et al9 described an LOA to cavernous sinus lesions, exposing the entire cavernous sinus lateral wall from the superior orbital fissure (SOF) anteriorly to Meckel’s cave posteriorly, as well as to the middle fossa floor by removing greater sphenoid wing. More recently, other authors have described an endoscopic LOA to the same anatomical regions for extradural as well as intradural lesions.10 , 11 All of these modifications shared removal of the lateral orbital rim and possibly the lateral orbital wall depending on the location of the lesion within the orbit.
13.2 Relevant Surgical Anatomy
The bony orbit is formed by the frontal, zygomatic, sphenoid, maxillary, lacrimal, ethmoid, and palatine bones. The lateral orbital rim is formed anteriorly by the zygomatic process of the frontal bone and the frontal process of the zygomatic bone. The lateral orbital wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid bone. The distance from the lateral orbital rim to the SOF and anterior portion of the cavernous sinus measures approximately 4 to 4.5 cm (Fig. 13.1).12 The greater wing of the sphenoid also forms the majority of the middle fossa floor and the roof of the infratemporal fossa. The lateral wall is continuous anteriorly with the orbital roof and floor but is separated posteriorly from the roof by the SOF and from the floor by the inferior orbital fissure (IOF). The zygomatic nerve is a branch of the maxillary division of the trigeminal nerve. It arises from the pterygopalatine ganglion and carries sensory fibers from the cheek and temple as well as postganglionic parasympathetic fibers from the greater superficial petrosal nerve to the lacrimal gland. It passes through the IOF along the lateral orbital wall and divides into the zygomaticotemporal and zygomaticofacial branches. These two branches enter the zygomatico-orbital foramina in the lateral wall of the orbit and exit through the zygomaticotemporal foramen to the temple skin and zygomaticofacial foramen to the cheek skin, respectively. In some cases, the lacrimal foramen can be found in the lateral orbital wall anterior to the lateral extent of the SOF through which a recurrent branch from the ophthalmic artery or lacrimal artery extends to the periorbital or meninges of the temporal dura.
Fig. 13.1 Orbital dimensions and volume. Distance from the lateral orbital rim to the superior orbital fissure and the anterior portion of the cavernous sinus measures 4 to 4.5 cm. The distance from the posterior edge of the zygomatic bone to the lateral orbital wall measures 2 cm. (Reproduced with permission from Rontal E, Rontal M, Guilford FT. Surgical anatomy of the orbit. Ann Otol Rhinol Laryngol 1979;88:382.)
At the superior and medial aspect of the orbital apex, the optic foramen is formed by the lesser wing of the sphenoid and the body of the sphenoid. In the optic foramen, the ophthalmic artery originates from the internal carotid artery intradurally just distal to the distal dural carotid ring in most cases, enters the optic foramen in the inferomedial aspect of the optic nerve before passing inferior and lateral to the nerve in the canal, and finally courses superior and medial to the nerve in the orbit.13 The medial and posterior extension of the lesser wing of the sphenoid is the anterior clinoid process. The anterior clinoid process has three roots at its base: the anterior root connected to the planum, the lateral root connected to the lesser wing, and the posterior root connected to the sphenoid body. These roots form the superior, superolateral, and inferolateral borders of the optic foramen, respectively. The posterior root of the anterior clinoid process is oblique and is known as the optic strut. It separates the optic foramen from the SOF, which is located in the inferior and lateral aspects of the orbital apex. It has a wide base medially and narrow apex laterally. It is bounded medially by the sphenoid bone, superomedially by the optic strut, superiorly by the lesser wing of the sphenoid, and inferiorly by the greater wing of the sphenoid. In the most lateral aspect of the fissure, a small part of the frontal bone forms the lateral boundary of the fissure. The lower margin of the SOF is separated from the foramen rotundum by a ridge of bone called the maxillary strut, and the fissure blends medially into the IOF.
The optic sheath, the dura of the SOF, and the periorbita merge together and form the tendinous ring. This ring surrounds the optic foramen and part of the SOF and gives the origin of superior, inferior, and lateral rectus muscles. The ophthalmic artery and the optic, oculomotor, abducens, and nasolacrimal nerves traverse through the tendinous ring, whereas the frontal, lacrimal, and trochlear nerves enter through the SOF but outside the ring. The optic nerve passes medially in the tendinous ring below the levator palpebral superiors and the lateral rectus muscle. The oculomotor nerve courses in the medial aspect of the fissure just lateral to the optic strut and divides into superior and inferior divisions in the SOF. The abducens nerve passes through the SOF and tendinous ring medial to the ophthalmic division of the trigeminal nerve and then courses laterally to enter the medial surface of the lateral rectus muscle. The nasociliary nerve arises from the medial side of the ophthalmic division and runs in between the superior and inferior oculomotor nerves and then superior to the optic nerve to reach the medial wall of the orbit where is divides into the anterior ethmoid, posterior ethmoid, and infratrochlear nerves. The ophthalmic division of the trigeminal nerve branches into three nerves—the lacrimal, frontal, and nasociliary nerves—as it exits the cavernous sinus. The lacrimal nerve passes lateral to the frontal nerve in the SOF and then on the superior margin of the lateral rectus muscle to the lacrimal gland. The frontal nerve passes through the SOF medial to the lacrimal nerve and below the trochlear nerve and then divides into the supratrochlear and supraorbital nerves running above the superior oblique and the levator palpebral superior muscles toward the superior orbital rim (Fig. 13.2). The trochlear nerve enters the lateral part of the SOF outside the tendinous ring, below the oculomotor nerve and above the ophthalmic division of the trigeminal nerve, and then courses medially above the frontal nerve to the superior oblique muscle. The infraorbital and zygomatic nerves are the two divisions of the maxillary nerve in the pterygopalatine fossa. These two nerves traverse through the IOF into the orbit. The infraorbital nerve passes through a groove in the floor of the orbit to the infraorbital foramen. The zygomatic nerve passes in the lateral wall of the orbit and divides into zygomaticotemporal and zygomaticofacial nerves exiting through their respective foramens in the lateral orbital wall.14 , 15
Fig. 13.2 Cadaveric lateral view of the left cavernous sinus and superior orbital fissure. Opening of the lateral wall of the cavernous sinus demonstrating the relationship between the oculomotor nerve and its divisions (CN III), the trochlear nerve (CN IV), the ophthalmic nerve and its divisions (V1), and the abducens nerve (CN VI) as they enter the superior orbital fissure. (Reproduced with permission from Rhoton A. The orbit., Neurosurgery 2002;51[Suppl 1]:303–334, Fig. 13.7.3 (c).)
13.3 Indications
The LOA is indicated for orbital decompression for some orbital pseudotumors, thyroid-related eye disease, and tumorous lesions presenting themselves in the lateral and superolateral orbital compartment without significant intracranial component.7 , 13 With introduction of the microsurgical techniques, lesions located within the SOF, those superior, lateral, and inferior to the optic nerve in the optic canal,7 and those in the cavernous sinus9 and middle fossa16 can be approached through an LOA. When combined with supraorbital mini craniotomy with or without the addition of superolateral orbital rim osteotomy, lesions in the suprasellar cistern and anterior circulation can also be addressed with this approach.8
13.4 Surgical Technique
The patient is positioned supine on the operative table with the head held in a rigid three-point fixation head holder. The head is turned 0 to 20 degrees to the contralateral side with a slight head extension depending on the location of the lesion. For example, lesions located purely in the lateral orbital compartment require more contralateral rotation but those located more posteriorly in the middle fossa require less. Similarly, lesions involving the clinoid require more head extension to improve the visual trajectory during clinoidectomy. Stereotactic image guidance is used to aid localization during surgery.
The eyes are lubricated, and a protective eye shield is placed in the ipsilateral eye. The skin incision is marked along the skin crease in the upper eyelid extending laterally along the zygomatic arch for about 2 cm. A small, forked incision extending toward the inferior eyelid may be added to allow for more skin relaxation and orbital content retraction. The lateral canthal ligament may be kept intact along with the lateral eyelids commissure. The incision along the zygomatic arch can be extended as far posteriorly as 2.4 cm from the lateral commissure without risking injury to the temporal branch of the facial nerve.17 The skin is prepped with ophthalmic solution. The skin incision is made down to the periosteal layer and then this layer is elevated to expose the lateral orbital rim without violating the periorbital. Dissection is continued to elevate the temporalis muscle laterally from the lateral orbital wall, and the periorbita is dissected medially to the SOF.
A length of 1.5 to 2 cm of the lateral orbital rim is marked and thin plates are placed, and screw positions are marked for the best cosmetic results at the end of the surgery. A C1 drill bit is used to make the bony cuts superiorly just above the frontozygomatic suture and inferiorly at the junction of the frontal process with the body of the zygoma while protecting the orbital contents and then the rim is fractured and removed (Fig. 13.3). Alternatively, in cases where the lateral wall is thickened, a drill bit can be used to connect both cuts posteriorly, preserving the rim. When the superior orbital rim needs to be included to approach lesions around the anterior clinoid or in the suprasellar cistern, a burr hole is made in MacCarty point to expose the frontal dura and the periorbita, and a B1 drill with footplate attachment is used to turn a one-piece bone flap.
