Tumors of the Orbit

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CHAPTER 147 Tumors of the Orbit

Paul A. Gardner, Joseph C. Maroon, Amin B. Kassam

A variety of lesions can affect the orbit (Table 147-1). These lesions have variable clinical manifestations, operative indications, and treatment options, all of which are determined by the pathology. Orbital tumors can occur in all areas of the orbit, and surgical approaches must be available to provide 360 degrees of access.

TABLE 147-1 Incidence of Orbital Tumors and Pseudotumors at the Senior Author’s Institution over a 12-Year Period

Spheno-orbital meningioma	135
Hemangioma	101
Optic nerve/orbital meningioma	60
Neurofibroma	39
Optic nerve glioma	39
Lymphangioma	36
Dermoid	28
Benign mixed lacrimal gland	21
Hemangiopericytoma	20
Rhabdomyosarcoma	12
Adenoid cystic carcinoma	10
Arteriovenous malformations	8
Fibrous histiocytoma	7
Venous varices	7
Cholesteatoma	3
Metastatic tumor	185
Nonspecific orbital inflammation	180
TOTAL	891

Advances in imaging and surgical approaches have significantly changed the management of orbital disease. Biopsy is not always needed, but when indicated, it can often be performed with minimally invasive techniques. Endoscopic endonasal approaches (EEAs) complement the traditional microsurgical approaches for biopsy or resection and hold the potential to reduce morbidity. This chapter outlines the clinical findings of patients with common orbital lesions, the relevant surgical anatomy, and options for surgical approaches.

Clinical Manifestations

Tumors that involve the orbit can be classified into two major groups: primary tumors of the orbit and tumors with other sites of origin that extend into the orbit. The most frequent primary orbital tumors in adults include lymphoid tumors, cavernous hemangiomas, and meningiomas, whereas dermoid cysts, capillary hemangiomas, and rhabdomyosarcoma predominate in children (see Table 147-1).¹ The most common tumors that extend into the orbit are meningiomas, followed by sinonasal carcinomas. The most frequent initial symptom of an orbital mass is proptosis, which occurs in 44% of patients. Change in visual acuity is often a late finding or indicates a tumor that is close to the orbital apex or optic nerve.¹

Orbital tumors can also be divided into three categories based on their location within the orbit: (1) intraconal (within the extraocular muscle cone), (2) extraconal, and (3) intracanalicular (within the optic canal), with differing features based on these locations. Intraconal tumors tend to cause early vision loss and impairment of ocular motility, as well as axial proptosis. These effects result from direct pressure on the optic nerve and impingement on extraocular muscles. Extraconal tumors cause proptosis as an early manifestation. Visual impairment occurs late as a result of tumor involvement of the optic nerve or the individual muscles and deformity of the globe itself. Finally, intracanalicular tumors cause early vision loss, papilledema, and the appearance of optociliary shunt vessels on the surface of the optic discs. These tumors cause minimal or no proptosis.²

Surgical Anatomy

The orbit is a cone-shaped structure with an approximate volume of 30 cm³. The base of the cone is quadrangular, with its widest dimension just posterior to the orbital rim. The apex is formed by the optic canal (containing the optic nerve and ophthalmic artery) and superior orbital fissure (gateway for the superior and inferior divisions of the oculomotor nerve, the trochlear nerve, branches of V1, the abducens nerve, the superior ophthalmic vein, and sympathetic fibers from the cavernous sinus) (Fig. 147-1). The orbit is composed of seven different bones. Its roof is part of the frontal bone, and the floor consists of parts of the maxilla and zygoma. Its lateral wall is formed by the zygoma and greater sphenoid wing, and the medial wall has contributions from the maxilla, lacrimal bone, and ethmoid bone. Medially, the sphenoid and ethmoid sinuses border the inner aspect of the cone, as well as the optic canal.

FIGURE 147-1 Anterior view of the orbit showing the contents of the optic canal (optic nerve and ophthalmic artery) and superior orbital fissure (superior and inferior divisions of the oculomotor nerve, trochlear nerve, branches of V1, abducens nerve, superior ophthalmic vein, and sympathetic fibers from the cavernous sinus), as well as the various attachments of the extraocular muscles to the annulus of Zinn. IR, inferior rectus; LPS, levator palpebrae superioris; LR, lateral rectus; MR, medial rectus; SO, superior oblique; SR, superior rectus.

The optic canal is approximately 4.5 mm wide and 5 to 10 mm long and has an average height of 5 mm, although its diameter and the thickness of its walls vary throughout its length. Several anatomic landmarks should be noted because they have significant surgical relevance. The optic strut is a bony ridge that runs between the anterior clinoid process (lesser wing of the sphenoid) and the sphenoid bone and sinus. This strut forms the inferior/lateral border of the optic canal and separates the optic canal from the superior orbital fissure. The proximal, dorsal opening is a fold of dura called the falciform ligament. The optic nerve travels approximately 15 mm in the subarachnoid space from the chiasm to the falciform ligament.

The intracranial dura enters the canal as a combined dural-periosteal layer before splitting into the dura of the optic nerve (sheath) and the periorbita. The intracranial arachnoid is separate through the optic canal but fuses with the pia at the globe. At the orbital portion of the optic canal, the pia and arachnoid are joined together dorsomedially and fuse to the dura and annulus of Zinn ventrally. This tethers the optic nerve and partially occludes the subarachnoid space. The fibrous annulus of Zinn tethers the origin of four of the seven extraocular muscles (all four rectus muscles). The levator palpebrae muscle originates from the posteromedial orbit, the superior oblique muscle has its origin high on the medial wall of the orbit near the apex, and the inferior oblique originates from a position just lateral to the anterior lacrimal crest.

The ophthalmic artery, which provides the major blood supply to the optic nerve, arises from the supraclinoid internal carotid artery (ICA) and passes laterally and inferior to the optic nerve in the optic canal (Fig. 147-2). It then assumes a more medial position as it enters the orbit. Understanding of the course of the ophthalmic artery is critical whenever the orbital apex is approached surgically. It gives rise to a major intraneural branch, the central retinal artery, 8 to 15 mm posterior to the globe, which penetrates the medial midportion of the nerve and provides the sole blood supply to the retina. The intraorbital optic nerve is supplied by a pial plexus derived from the ciliary arteries. The intracranial and intracanalicular portions of the optic nerve are supplied by fine perforators arising from the ICA and superior hypophysial artery. The superior and inferior ophthalmic veins provide the major drainage for the orbit. The superior ophthalmic vein passes over the lateral rectus muscle and through the superior orbital fissure before entering the cavernous sinus. The inferior ophthalmic vein forms from venous channels in the floor and medial wall of the orbit before anastomosing with the superior ophthalmic vein and pterygoid plexus.

FIGURE 147-2 Vascular supply of the orbit and optic nerve. Note how the ophthalmic artery passes lateral and inferior to the optic nerve before running medially as it enters the optic canal. The central retinal artery also assumes a medial course as it supplies the nerve.

Surgical Approaches (Lateral and Medial Corridors)

The guiding principle when choosing a surgical corridor is to avoid working across or around nerves. Specifically, when selecting orbital approaches one should avoid crossing the plane of the optic nerve. Therefore, orbital pathology lateral to the optic nerve is accessed via lateral orbitotomies, and medial pathology is accessed via medial orbitotomies. These medial corridors can be created through either external approaches (such as the anterior medial micro-orbitotomy or transfacial approaches) or endonasal corridors.

Traditional, external approaches to the orbit provide excellent access to tumors that are superior and lateral to the optic nerve and orbit. Tumors with lateral intracranial extension (a significant number of orbital tumors) are best accessed by a pterional or fronto-orbital temporal craniotomy with or without orbitozygomatic osteotomies. Another variant is the lateral microsurgical approach, which provides very good access for orbital tumors lateral to the optic nerve and apex.

For tumors located very anteriorly in the orbit, an anterior-medial micro-orbitotomy is the traditional approach for resection. However, accessing the posterior intraconal space from an anterior approach often involves detaching the medial rectus muscle and performing a lateral orbitotomy to allow mobilization of the cone.

Endoscopic assistance through standard external approaches was used to improve visualization as early as the 1980s.³ Endoscopic endonasal orbital and optic nerve decompression has become accepted treatment of thyroid eye disease and traumatic optic neuropathy unresponsive to steroids.⁴^–⁹ Sporadic cases of endoscopic decompression, biopsy, and resection of tumors that involve the orbit have been reported.¹⁰^–¹⁹ The EEA has been extended to permit resection of all types of skull base tumors, including posterior, middle, and anterior fossa intradural tumors.²⁰^,²¹ EEAs provide excellent access for intraconal and extraconal tumors that are medial and inferior to the optic nerve and can be applied to any median intracranial extension, provided that key neurovascular structures (such as the optic nerve) remain lateral to the tumor. In addition, EEAs provide access to most of the orbit, from the posterior globe to the orbital apex.

Combined, the aforementioned approaches provide 360 degrees of access to the entire orbit, with selection of the approach guided primarily by avoidance of crossing the optic nerve (Fig. 147-3).

FIGURE 147-3 Illustration demonstrating how external and endonasal approaches combine to provide complete, 360-degree access to the orbit. Frontotemporal craniotomy with orbital osteotomy accesses the orbit from 9 to 1 o’clock, the lateral microsurgical approach provides access to the orbit from 8 to 10 o’clock, and the addition of a zygomatic osteotomy to either of these approaches extends access to 6 to 8 o’clock. The medial micro-orbitotomy approach accesses the anterior orbit from 1 to 5 o’clock, and the endoscopic endonasal approaches provide access to the mid and posterior orbit from 1 to 7 o’clock.

Lateral Corridors

External Approaches

Fronto-orbital Temporal and Pterional Transcranial Approaches

The frontotemporal incisions and scalp flap elevation are designed according to the particular need for orbital access. A standard pterional incision (curvilinear, just anterior to the tragus to the midline apex of the anterior hairline) is usually adequate to access the superolateral orbit. However, to extend the access medially to the superior orbit or inferiorly/laterally, the incision should be at least a modified bicoronal one extending from the tragus on the side ipsilateral to the pathology to the contralateral superior temporal line or even to the contralateral tragus (Fig. 147-4). An imaginary line drawn between one end of the incision and the other should cross the orbital region of interest. The entire scalp flap should be elevated in a subperiosteal plane over the frontoparietal area and the superficial layer of the deep temporal fascia. We incise this fascia, which is continuous with the periosteum of the orbitozygomatic complex, by following an imaginary line from the superior orbital rim to the root of the zygoma. Elevation of the scalp/facial flap continues deep relative to this plane (i.e., subperiosteally) to protect the frontal branches of the facial nerve. Elevation with inferior retraction of the temporalis muscle exposes the lateral orbit. The muscle can easily be dissected from the underlying squamosal bone by starting the dissection at the root of the zygoma after making a posterior incision in the muscle and dissecting inferiorly to superiorly in the direction of the fascial attachments rather than against them as is traditionally done. This provides a much cleaner dissection and may help preserve some of the microvascular supply to the muscle, thus decreasing atrophy. If any part of the zygoma will be removed for access, the corresponding attachment (origin) of the masseter muscle is transected. Its fascia is incised and elevated from the muscle (parotid-masseteric fascia). Dissection of the muscle is then completed by electrocautery while using a malleable retractor to protect the temporalis muscle, which lies deep relative to the masseter.

FIGURE 147-4 Partial bicoronal skin flap for the fronto-orbital temporal transcranial approach with unilateral orbitotomy. A, Approximate skin incision overlying the craniotomy. B, Superior view of the tumor accessed via this approach, with both intracranial and orbital components. C, The subperiosteal dissection should be carried onto the orbit and around its rim to dissect the periorbita from the inner wall of the orbit. D, Superolateral view showing access to the frontal and temporal dura, as well as the superolateral orbit, with the supraorbital neurovascular bundle freed and retracted with the orbit. E, Orbitotomy cuts can be made with the craniotomy, but the posterior osteotomy can be performed in more controlled fashion if the two are done separately.

The subperiosteal dissection should be carried onto the orbit and around its rim to dissect the periorbita from the inner wall of the orbit. There is always periorbital adherence at the superolateral corner of the zygomaticofrontal suture. Dissecting all areas around the orbit at the same depth before deepening the dissection prevents inadvertent tears in the periorbita. The supraorbital neurovascular bundle should either be dissected from its notch or, if in a true foramen, be freed with diagonal osteotomies (inverted V) directed away from the nerve. This technique allows the nerve to be moved freely away from the orbital bone.

Next, a standard frontotemporal craniotomy is performed. The lateral bone of the greater wing of the sphenoid is then dissected free from the dura and removed with rongeurs and a high-speed drill until flush with the orbit. Bone removal should stop at the depth of the orbitomeningeal artery to prevent inadvertent injury to the contents of the superior orbital fissure. The orbitomeningeal artery is an important landmark marking the “tip of the iceberg,” with the superior orbital fissure lying beneath. At this point the frontal dura can be dissected free from the roof of the orbit so that the orbital bone is freed from dura on one side and periorbita on the other before performing the orbital osteotomies. We prefer to use a reciprocating saw for the orbital osteotomies while protecting the brain and orbit with malleable retractors (“brain ribbons”). The saw is inserted into the orbit and the cut is made from the orbit toward the frontal dura. The medial cut is usually at or just lateral to the supraorbital notch. The lateral cut is made by inserting the tip of the reciprocating saw into the inferior orbital fissure and completing an osteotomy from within the orbit at a level just above or through the zygomatic prominence, as needed. The final posterior osteotomy is completed with a small drill bit from the brain side while protecting the orbit with a ribbon. This cut is made from the posterior aspect of the medial osteotomy across the roof of the orbit, through the remaining sphenoid wing, and connected laterally to the lateral osteotomy in the inferior orbital fissure. These osteotomies should be extended as posterior as possible to prevent loss of orbital bone, which would require reconstruction to prevent enophthalmos. At this point the orbitozygomatic complex can be freed from any remaining soft tissue attachment and removed to provide access to the entire superolateral orbit, as well as the regional frontotemporal dura and related brain region, if needed (Fig. 147-5). It is important that the posterior portion of the superior orbit be removed adequately because this bone can prevent adequate dural retraction and defeat any advantage of the superior orbitotomy.

FIGURE 147-5 Frontotemporal craniotomy and orbitotomy provide access to the entire superolateral orbit, as well as to the regional frontotemporal dura and related brain region.

This approach is ideal for tumors such as meningiomas with both intracranial and orbital components (see Fig. 147-3). If intracranial access is desired, after opening the frontotemporal dura, multiple retraction stitches can be applied across the internal surface of the dura to retract the orbit inferiorly. If the middle cranial fossa dura is involved or there is significant superior extension, the addition of zygomatic osteotomies can be advantageous. This allows more aggressive removal of subtemporal bone and access to the basal foramina and decreases brain retraction when addressing superiorly extending lesions by allowing a more inferior to superior angle of dissection. We prefer to remove the orbit and zygoma as one piece with a straight osteotomy through the main portion of the zygoma and a diagonal cut flush with its posterior attachment to the temporal bone (root of the zygoma). A variant of the approach just described is a “one-piece cranio-orbitozygomatic approach” wherein the craniotomy and orbitozygotomy are done as one piece; it is reported to potentially improve cosmetic outcomes. We have not found cosmesis to be an issue with the “two-piece” approach, however, because defects are easily reconstructed with titanium mesh and plates.

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