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| REVIEW ARTICLE |
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| Year : 2021 | Volume
: 4
| Issue : 3 | Page : 78-91 |
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Orbital tumors: Current neurosurgical perspectives
Priyadarshi Dikshit, Maruti Nandan, D Balachandar, Awadhesh K Jaiswal, Sanjay Behari
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, UP, India
| Date of Web Publication | 02-Nov-2021 |
Correspondence Address:
Dr. Sanjay Behari
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, UP
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/IJNO.IJNO_413_21
Orbit can be home for a spectrum of tumors with almost every orbital structure having the potential to harbor a neoplastic process. Surgical exposure and resection of orbital tumors can often be tricky due to the intricate anatomy of the region, with an additional complexity caused by a tumor related distortion. The clinical presentation depends on the primary structure involved and the location of the tumor within the orbit, and so does the scheme of management. Modern diagnostic imaging modalities offer a crucial pre-operative understanding of the precise location of the tumor within the orbit; it also helps in defining the nature of the tumor. Both these aspects are required for planning the appropriate surgical approach. Often, orbital tumors extend beyond the confines of the orbit requiring the tailoring of the surgical procedure, which may necessitate the involvement of a multidisciplinary team. The contemporary neurosurgical practice is also witnessing a progressive inclination towards minimally invasive endoscopic approaches, which have shown equally good if not better results in properly selected cases. Furthermore, early promising results with attempts at performing multisession stereotactic radiosurgery on orbital tumors has rekindled interest in this modality, in line with the management of intra-cranial tumors having a similar pathology. This article aims to recapitulate relevant surgical anatomy and to elucidate the current practice in the management of common orbital tumors encountered by neurosurgeons.
Keywords: Orbital tumors, surgical approaches, diagnosis, endoscopy of orbit, anatomy of orbit
How to cite this article:
Dikshit P, Nandan M, Balachandar D, Jaiswal AK, Behari S. Orbital tumors: Current neurosurgical perspectives. Int J Neurooncol 2021;4, Suppl S1:78-91 |
The orbit is a compact space encasing the globe, the optic nerve, multiple neuro-vascular structures, and complex musculotendinous structures, all of which are required for the precise orchestration of ocular movements. Tumors spanning a wide spectrum can originate in this anatomical region. The structure of origin and location in a particular surgical space dictate the clinical presentation. Modern diagnostic imaging modalities can quite precisely characterize the tumor type, its location within or outside the muscle cone, and can demonstrate relationships with adjacent neuro-vascular structures, an information crucial for surgical planning. Common categories of orbital tumors encountered in contemporary neurosurgical practice include: (i) tumor at the orbital apex and the optic canal, (ii) intra-cranial tumors with extension into the orbit, or vice versa, (iii) extra-ocular intra-orbital and intraconal tumors, as well as (iv) tumors of the orbital wall/paranasal sinuses. Management in detail of each of the tumor pathology that may be encountered is beyond the scope of this article. This article aims to review the commonly used approaches to the orbit used by neurosurgeons in contemporary practice.
| Anatomy | |  |
The credit for the present-day insights into the orbital anatomy goes to the devoted investigation done by great anatomists like Zinn, Sabatier, Sappey and Lockwood.[1],[2] The orbit can be envisaged as a recumbent pyramid having four walls, with its quadrangular base opening anteriorly and the apex inclining postero-medially [Figure 1]. The average orbital volume in an adult is around 30cc, of which the globe occupies roughly 7cc.[3],[4] Orbital volume is smaller in the pediatric age group and finally attains the adult size by the age of 12 years. | Figure 1: Schematic representation for understanding of orientation of bilateral orbits, envisaging them as recumbent pyramids. The lateral walls of bilateral orbits subtend an angle of approximately 90 degrees with each other, while the medial walls are parallel to each other. The orbital roof forms the floor of the anterior cranial fossa; and, both orbits sandwich the nasal cavity and paranasal sinuses between them. The roof of the maxillary air sinus forms the floor of the orbit. Bilateral orbits communicate with the middle cranial fossa via the optic canal and the superior orbital fissure. The inferior orbital fissure provides communication with the pterygopalatine fossa and infratemporal fossa
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Awareness of development of the para-nasal sinuses is required while planning approaches to the orbit, especially in pediatric patients. The maxillary sinuses are the first to develop with a biphasic growth occurring between 0-3 years and 7-12 years of age, matching with the biphasic growth of the orbit. The ethmoid sinuses attain adult size at the age of 12 years, while the frontal sinuses begin pneumatizing at the age of 7 years, increasing in size till early adulthood.[5],[6]
Orbital anatomy follows the rule of 7, with 7 bones, 7 muscles, and 7 nerves.[7] The orbital walls are formed by the following 7 bones [Figure 2], [Figure 3]: (i) Orbital plate of frontal bone (separates orbit from the anterior cranial fossa), (ii) ethmoid (lamina papyracea), (iii) lacrimal bone, (iv) palatine bone (orbital process), (v) maxilla, (vi) sphenoid (greater and lesser wings), and (vii) zygomatic bone. The muscles include the superior, medial, inferior and lateral recti, the superior and inferior obliques, and the levator palpebrae superioris muscles. The nerves include the optic nerve, the oculomotor nerve, the abducens nerve, the trochlear nerve, and the lacrimal, frontal and nasociliary branches of the ophthalmic division of trigeminal nerve. | Figure 2: Schematic diagram demonstrating the osseous anatomy of the walls of orbit (left orbit). 1a: Orbital plate of the frontal bone, 1b: Superior orbital rim is formed by the frontal bone and harbors the frontal sinus medially; and, the zygomatic process articulates with the zygomatic bone in the lateral rim of orbit. The superior orbital fissure (10) lies between the greater wing (2a) and the lesser wing of the sphenoid (2b) and is separated from the optic canal (9) by the optic strut; 3: Zygomatic bone; 4: Maxilla; 5: Orbital process of the palatine bone; 6: Ethmoid; 7: Lacrimal bone; 8: Infra-orbital groove leading to the infra-orbital foramen (13); 14: Pyriform aperture; 15: Annulus of Zinn
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 | Figure 3: Anatomy and three-dimensional relationships of the posterior orbit: 1: Optic canal; 2: Superior orbital fissure; 3: Inferior orbital fissure; 4: Maxillary sinus; 5: Greater wing of sphenoid which forms the lateral wall of the orbit anteriorly (5a) and forms the floor and lateral wall of the middle cranial fossa posteriorly (5b); 6: Zygomatic arch (cut) and infratemporal fossa (white asterisk) ; 7: Anterior cranial fossa separated by the orbital plate of frontal bone (white arrowhead); 8: Frontal sinus; 9: Ethmoidal air cell and a small orbito-maxillary (Haller's) air cell lateral to it (black asterisk); 10: Middle turbinate (cut); 11: Nasal septum; 12: Pterion; 13, 14: Contralateral middle and inferior turbinate
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The orbital rims form the base of the pyramid, which on an average in an adult orbit measures approximately 4 cm horizontally and approximately 3.5 cm vertically. The superior orbital rim is formed by the frontal bone, bears the frontal sinus medially, and features the supra-orbital notch/foramen (containing the supraorbital nerve and artery). The superior rim overhangs to some degree below the level of orbital roof. Periorbita elevation in this region should be done carefully to avoid tear of the periorbita.
The medial rim is formed by the maxillary process of the frontal bone and the frontal process of the maxilla. Close to the medial orbital margin on the medial orbital wall lies the groove for the nasolacrimal duct. The inferior rim is formed by the maxilla and the zygomatic bone. Toward the inferior orbital margin on the floor of the orbit, the infra-orbital groove leads to the infra-orbital foramen. The lateral rim is formed by the zygomatic process of the frontal bone and the frontal process of the zygomatic bone meeting at the fronto-zygomatic suture, an important surgical landmark. The lateral orbital tubercle (Whitnall's tubercle) located on the inner aspect of the lateral orbital margin is easily palpable and is about 1 cm below the level of fronto-zygomatic suture and is the site of attachment of the lateral palpebral ligament.
The orbit has 4 walls: roof, medial wall, floor, and lateral wall. The roof is mainly formed by the frontal bone, and near the apex, by the lesser wing of sphenoid bone. It separates the orbit from the anterior cranial fossa (ACF) and often harbors the frontal sinus in its anterior part sandwiched between the ACF base and the orbit. The frontal sinuses are almost always asymmetric and usually have two compartments, a vertical compartment in the squamous part of the frontal bone and a horizontal one in the orbital plate. However, they may have up to three compartments.[8] The pneumatization of orbital plate of the frontal bone may range from agenesis of the frontal sinus to complete pneumatization of the ACF, an anatomical variation of relevance for the trans-cranial approaches. The orbital plate of the maxillary bone forms most of the orbital floor and separates the orbit from the maxillary air sinus; the palatine and zygomatic bones also contribute to the floor.
The medial wall of orbit is thin and separates the orbit from the ethmoidal air cells anteriorly and the sphenoid sinus posteriorly. It is composed of four bones: maxillary, lacrimal, ethmoid, and medial part of the lesser wing of sphenoid. The medial wall of the orbit (lamina papyracea) also features the anterior and posterior ethmoidal foramina through which like-named vessels pass. The lateral wall of the orbit is formed by fronto-sphenoid process of the zygomatic bone anteriorly and the greater wing of the sphenoid posteriorly. The temporal fossa surface of this wall of orbit provides attachment to the temporalis muscle [Figure 4]. | Figure 4: Photograph of skull showing postero-lateral view of the orbit as seen from the temporal region. 1: Lateral orbital rim formed by the frontal process of the zygomatic bone; 2: Zygomatic bone forming the anterior part of the lateral wall of the orbit. 3: Greater wing of the sphenoid, with a shallow identifiable groove (white arrowhead), which marks the separation between the middle cranial fossa and orbit; 4: Body of the zygomatic bone; 5: Maxilla with the inferior orbital fissure (white straight arrow) and the pterygo-maxillary fissure (white curved arrow); 6: Zygomatic arch; 7: Lateral pterygoid plate with adjacent infratemporal fossa (white asterisk); 8: External auditory meatus. Blue dashed line marks the position of the anterior cranial fossa base, that is, the roof of orbit
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The orbital apex is directed medially and in an oblique fashion and features three important inlets through which it communicates with the middle cranial fossa and the infratemporal fossa:
- The optic canal bridges the intracranial space and orbit, passing inferomedial to the anterior clinoid process. It is bordered laterally by the optic strut that separates it from the superior orbital fissure. It is approximately 4.5 mm wide and 5-10 mm long with an average height of 5 mm [Figure 5]. The proximal, dorsal opening of optic canal is roofed by 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 duramater enters the canal as a combined dural-periosteal layer before splitting into the dura of the optic nerve (optic nerve sheath) and the periorbita lining the orbital walls.
- The superior orbital fissure is bordered infero-laterally by the greater wing of the sphenoid, and supero-medially by the lesser wing of the sphenoid. It transmits the cranial nerves IIIrd, IVth, Vth and VIth, the sympathetic nerve plexus and the superior ophthalmic vein.
- The inferior orbital fissure lies inferior to the superior orbital fissure, featuring in the lateral part of the floor of the orbit. It is bound anteriorly by the maxilla, postero-superiorly by the greater wing of sphenoid, laterally by the zygomatic bone, and medially by the body of sphenoid. It transmits the zygomatic branch of maxillary nerve and ascending branch of the pterygopalatine ganglia.
 | Figure 5: Schematic diagram showing the superior view of bilateral orbits after removal of the roof and periorbita. 1: Optic nerve, crossed by the distal portion of ophthalmic artery; 2: Superior rectus; 3: Medial rectus; 4: Superior oblique; 5: Levator palpebrae superioris; 6: Lateral rectus; 7: Adipose body of the orbit (intra-conal portion); 8: Optic canal with the optic strut (9) separating it from the superior orbital fissure; 10: Middle cranial fossa; 11: Ethmoidal air cells; 12: Temporalis muscle
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The fibrous annulus of Zinn (common tendinous ring) forms the origin of four out of seven extraocular muscles (all the four recti). It encloses the apical part of the superior orbital fissure and the orbital end of the optic canal. The enclosure-through within the annulus is known as the oculomotor foramen. The levator palpebrae muscle originates from the posteromedial orbital roof, while 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 optic nerve has four defined segments, namely the intra-ocular segment (1mm), intra-orbital segment (4-10 mm), and intra-cranial segment (10 mm). The intra-orbital optic nerve normally remains lax with a S-shaped configuration, which allows for ocular movements without undue stretching of the nerve.
The ophthalmic artery, which provides the major blood supply to the optic nerve, arises from the supra-clinoid internal carotid artery (ICA) and passes laterally and inferiorly to the optic nerve in the optic canal. It then assumes a medial position as it enters the orbit. 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 intracranial and intracanalicular portions of the optic nerve are supplied by fine perforators arising from the internal carotid artery (ICA) and the superior hypophyseal 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 is formed by venous channels in the floor and medial wall of the orbit before anastomosing with the superior ophthalmic vein and the pterygoid plexus.
 | Figure 6: Schematic diagram showing the location of various surgical spaces of the orbit. (i) Intraconal space (green shaded area); (ii) Peripheral space (yellow shaded area); (iii) Subperiosteal space (blue shaded area); (iv) Sub-Tenon's space (teal shaded area); and (v) Subarachnoid space (within the optic nerve sheath 1). 2: Tenon's fascia; 3: Fascia surrounding the muscle cone; 4: Periorbita
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 | Figure 7: A simple schematic diagram showing the important ligaments and tendons in the anterior orbit (left side). 1: Whitnall's ligament; 2: Aponeurosis of the levator palpebrae superioris and its medial (3) and lateral (4) horns; 5: Lateral canthal tendon attached to the Whitnall's tubercle; 6: Faint representation of the position of globe; 7: Medial canthal tendon; 8,9: Superior and inferior tarsal plates; 10: Lacrimal sac; 11: Ligament of Lockwood; 12: Trochlea
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 | Figure 8: A simplified diagrammatic representation of the orbital septa and fascial condensation in the posterior part of left orbit. 1: Optic nerve sheath; 2:Intra-muscular septum; 3: Annulus of Zinn. Note the delicate fascial bands connecting the optic nerve sheath with the surrounding fascial condensations. Thus, manipulation of the muscle cone can lead to traction on the optic nerve sheath. 4: Superior rectus; 5: Levator palpebrae superioris; 6: Superior oblique; 7: Medial rectus; 8: Inferior rectus; 9: Lateral rectus. The neuro-vascular structures at the region of orbital apex pass not only through the optic canal and superior orbital fissure but also through the annulus of Zinn, which acts as a second rigid channel [44]
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There are five surgical spaces within the orbit, namely the subperiosteal space (between the periorbita and the bone), the extraconal space, (between the periorbita and the muscle cone with its fascia, also known as the peripheral surgical space), the intraconal space, (within the muscle cone and its fascia), the sub-tenon's space, (between the Tenon's fascia and the globe) and the subarachnoid space, (between the optic nerve and its sheath). A single lesion may involve more than one space requiring a combination of approaches for its surgical management.
The intra-orbital structures are immersed in the orbital fat, also known as the adipose body of the orbit (ABO), which acts like a filling structure and aids in facilitating smooth ocular movements while providing adequate buoyancy and a “lubricating” function for the globe and extra-ocular muscles. Although the ABO is continuous throughout the orbit, it can be grouped into two types: one at the orbital apex and in the retrobulbar central zone having large fat globules and thin connective tissue septae, and the remaining zones having small, packed lobules with strong connective tissue septae. The intraconal portion of the ABO has extensions into the angles between the recti, and near the muscles and the orbital wall, where the ABO consists of small lobules. It also extends anteriorly as thin strips into the superior and inferior palpebrae.[9]
The extraconal space mainly contains densely packed adipose tissue (ABO) between the recti and the periorbita. On the medial aspect, the extraconal space contains the anterior and posterior ethmoidal vessels which often course over the superior border of the medial rectus muscle. The extraconal space also contains the lacrimal and frontal branches of the ophthalmic nerve, the trochlear nerve, the ethmoidal vessels, and the lacrimal gland. The intraconal compartment contains the ABO, optic nerve, oculomotor nerve divisions, nasociliary branch of the ophthalmic nerve, abducens nerve, ciliary ganglion, and ophthalmic artery.
The intraconal space can be assumed to be divided into the superior, inferior, medial, and lateral compartments by the optic nerve. The medial intraconal space can also be arbitrarily divided into three zones, based on the difficulty in accessing through the medial (endoscopic) approaches[10]:
Zone A: Antero-inferior to the inferomedial muscular trunk of the ophthalmic artery and an imaginary line through the middle of the medial rectus muscle. This zone has the easiest access of all medial zones and has very less neuro-vascular structures.
Zone B: Antero-superior to the line. This region is relatively critical due to the presence of anterior and posterior ethmoidal arteries, and some difficulty is encountered in order to work above the medial rectus muscle.
Zone C: This is behind the infero-medial trunk of the ophthalmic artery and is the most difficult of all medial regions to access owing to the compact space and proximity to the proximal ophthalmic artery and the optic nerve.
| Pathology | | |
Neoplasms can originate in any of the contents as well as in the walls of the orbit, and unsurprisingly, orbital tumors comprise a wide spectrum, reflecting the diversity of the occupants of the anatomical region ([Table 1] enlists the extra-ocular orbital tumors). Dermoid cysts and cavernous hemangioma are the most common benign tumors of the orbit accounting for about 1/5th of all orbital tumors, while lymphoma (non-Hodgkin) is the most common malignant neoplasm.[11],[12]
| Clinical Manifestations | | |
The most frequent initial symptom of an orbital mass is proptosis, which occurs in 44% of patients. This is followed by diplopia, another common early complaint. Change in visual acuity is often a late finding or indicates a tumor that is close to the orbital apex or the optic nerve.
Intraconal lesions present with an early vision loss, early impairment of ocular motility (double vision), and axial proptosis. In extraconal lesions, proptosis is the earliest manifestation, and displacement of the globe and compression of the extraocular muscles can produce diplopia, sometimes only in certain fields of gaze. Visual impairment occurs last, secondary to compression of the optic nerve and deformity of the globe. Intracanalicular tumors cause an early vision loss, optic nerve head swelling, and appearance of opto-ciliary shunt vessels on the surface of the optic discs with minimal or no proptosis.[15]
| Radiology | | |
The most common imaging modalities used for the evaluation of orbital lesions include computed tomogram and MRI. Multiplanar thin slice MRI with fat suppression (STIR and fat-sat®) and gadolinium enhanced images delineate the orbital soft tissue lesion and clearly depicts the orbital apex and optic pathway. CT scan is the preferred imaging modality for evaluating anatomy of the orbital wall, the paranasal sinuses, and to assess presence and extent of calcification and osseous involvement.
Each imaging pattern should be paid attention to as this has diagnostic significance [Table 2], [Table 3] and [Table 4]. Often, the shape of the lesion can also provide valuable information about the nature of lesion. In general, oval shaped lesions tend to be benign and cause displacement and deformation of the adjacent anatomical structures. There may be hyperostosis of the adjacent bone, as in the case of orbital meningiomas. In contrast, the malignant lesions tend to be irregular, infiltrative, and diffuse in nature with perineural involvement and bony destruction.[16],[17],[18],[19] | Table 2: Based on the location with respect to various surgical spaces of the orbit, the extra-ocular orbital tumors can be divided into three anatomical groups [Figure 9][14]
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Plain radiograph
The commonly used views for evaluation of orbital lesions include the Caldwell view, Water's view, Rhese view (for optic foramina) and lateral view. Usual radiological findings of orbital pathology are enlargement of the orbit and/or optic foramen, intra-tumoral calcification, adjacent hyperostosis/bone erosion.
Computed tomography (CT)
CT of the orbit with thin 1mm sections is used to evaluate the bone anatomy of the orbital wall and to study in detail the anatomy of adjacent para-nasal sinuses. CT, especially the three-dimensional (3D) CT, can also be used to objectively measure the degree of exophthalmos by Cabani's method. In this method, in the axial sections, a line is drawn across both orbits joining the outer canthus on each side. Care must be taken during acquisition of the CT scan to keep the plane of acquisition parallel to the Frankfurt plane, and the plane bisecting the lens is chosen. Usually, this line passes through the junction of anterior 2/3rd and posterior 1/3rd of the globe and the perpendicular distance from this line to the posterior surface at maximum convexity of cornea is calculated. Oculo-orbital index (OOI) is then calculated, which is defined by the ratio of length of the eyeball anterior to this intercanthal line and the total axial length. In normal person, this ratio is <70.
Exophthalmos grading
Grade I 70-100
Grade II 100
Grade III > 100
A numerical assessment of proptosis may also be carried out. A difference of >2mm of proptosis suggests significant asymmetry between the two eyes, and an absolute value of >21 mm suggests proptosis. This method, however, may not be accurate in extra-conal lesions, where there is eccentric proptosis, and a 3D CT measurement is preferred in such cases.[20],[21]
MRI orbit
Optic nerve is a white matter tract, and therefore, has similar characteristics as that of white matter on MRI image. MRI mainly delineates the soft tissue, that is, extraocular muscles, vitreous humor, optic nerve sheath complex and lacrimal gland. Axial, coronal, sagittal and oblique sections are used based on the individual diagnostic requirements. Sometimes a special plan called PNOTO (plan neuro-ocular, trans-occipital) may be utiized. Besides the routine sequences, the spin echo, fat suppression, and diffusion weighted images may also be utilized. MR angiography can be done to assess the vascularity associated with the orbital lesion.
B mode ultrasonography
This modality has been largely replaced by MRI of the orbit; however, if performed, it can add knowledge regarding the vascularity of the lesion and the cystic nature of the lesion.
| Surgical Approaches For Orbital Tumors | | |
Descriptions of surgery for orbital pathology utilizing the trans-cutaneous and trans-conjunctival pathway are available since the 18th century.[22] Lateral orbitotomy was first documented by Passavant and was later popularized by Krönlein, and Kennerdell in the early 20th century. [23],[24] The first narrative of trans-ethmoidal approach to the orbit was by Niho in 1970,[25] and on similar lines, an account of trans-frontal sinus path was shared by Colohan in 1985.[26] Sub-frontal approach for orbital tumors was advocated by Dandy, while the fronto-lateral pterional approach was familiarized by Naffziger in the 1940s, and later by Yasargil and Hassler.[27],[28],[29] Dolenc demonstrated approaches to the orbit for lesions having middle cranial fossa (parasellar) extensions by tracing the tumors after deroofing the orbit directly or by tracing from the superior orbital fissure.[30],[31]
Surgery for orbital tumors is complex due to location of the tumor often in the vicinity of delicate neuro-vascular structures and requires a good knowledge of the regional anatomy. In general, the goals of orbital surgery are:
- maximal safe resection of the tumor,
- preservation of vision and the ocular integrity,
- preservation of the ocular motor system,
- cosmesis (changes in ocular position and orbital margin and adjacent soft tissue injury as a sequel to surgical maneuvers can significantly influence the appearance of the patient).
In some cases, however, owing to the malignant potential/aggressiveness of the tumor and associated pre-operative vision loss, enucleation/orbital exenteration may be needed.
There exists no precise nomenclature system for approaches to orbit; however, orbital approaches have been broadly grouped traditionally into trans-orbital approaches and extra-orbital approaches. The trans-orbital approaches include: (i) anterior orbitotomy (without osteotomy), (ii) medial orbitotomy, (iii) lateral orbitotomy, and (iv) a combination of lateral and medial orbitotomy. The extra-orbital approaches include: (i) fronto-temporal approach, (ii) supra-orbital key-hole approach (SOKHA), (iii) inferior orbital approach, and (iv) extended endo-nasal approaches (EEA).[32]
Conventionally, the approaches to orbit have been explained with a clockwise relation to the globe.[33] [Figure 10] The following factors guide the choice of approach to orbital tumors: | Figure 9: Extra-ocular orbital tumors can be grouped into: (i) Extraconal tumors (lying outside the muscular cone). These can be sub grouped into: a: Sub-periosteal (between the bony orbital wall and periorbita), b: Extra-periosteal (tumor of the orbital wall ); and c: Peripheral surgical space tumors (tumor inside the periorbita but outside the muscular cone). (ii) Intra-conal tumors , which can be further sub-divided into: d: Medial, e: Central, and, f: Lateral, based on their relationship with the optic nerve
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 | Figure 10: Clockwise representation for approaches to orbital lesions. Tumors in the green shaded region (clockwise 6 to 1'O clock positions in the right eye) can be approached using the fronto-temporal craniotomy with orbito-zygomatic osteotomy; tumors in the yellow shaded area (8 to 10'O clock positions of right eye) can be exposed with a lateral orbitotomy; endoscopic endonasal approach can expose tumors in the blue shaded region (1 to 7'O clock positions in the right eye); tumors in the red shaded region (1 to 6 O' clock positions of the right eye) can be accessed using the medial micro-orbitotomy
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- Clockwise location of the tumor within the orbit and extent of orbital involvement
- Location in a specific orbital surgical space (intra/extraconal)
- Relationship with the optic nerve
- Pathological type of the tumor and the aim of surgery (for example, biopsy, partial or complete resection)
Anterior orbitotomy
Anterior orbitotomy refers to approaches through the eyelid or through the conjunctiva, and include the superior, medial, inferior, or trans-conjunctival approaches.[22] Anterior approaches are primary utilized for benign lesions limited to the anterior orbit, in juxtaposition to the globe and even for well-defined intraconal tumors located just behind the globe. Minimally invasive trans-conjunctival approaches have been described needing less surgical time, producing no visible scar. Excellent outcomes with these approaches have been published for intraconal hemangiomas and these approaches can be combined with eyebrow approach for adding exposure to all intraconal muscles. The risk of enophthalmos and fat herniation is less with trans-conjunctival approaches as the orbital wall is not removed. However, the trans-conjunctival approaches are not suited for tumors confined to the orbital apex, for tumors in the superior orbital region, and for relatively ill-defined tumors. [34],[35]
Superolateral approaches
The most often used surgical approaches by the neurosurgeons are the superolateral approaches, which include the lateral orbitotomy and the orbito-cranial approaches. These include the lateral orbitotomy, the supra-orbital craniotomy, and the pterional craniotomy with/without orbito-zygomatic osteotomy, and fronto-orbital modification of the supra-orbital keyhole craniotomy.
Lateral orbitotomy
This refers to removal of the lateral rim of the orbit and an approach via the lateral wall of the orbit. It can be used for lesions in the lateral peri-orbital space, and for extraconal and intraconal lesions located superior/lateral or inferior to the optic nerve. In the initial steps of this approach, after an upper lid crease incision (or a classical curvilinear incision beginning above the eyebrow and extending into the temporal region), the lateral canthal tendon is divided and the periosteum is elevated. Then, the anterior portion of temporalis muscle is elevated to expose the lateral orbital wall. The zygomatico-temporal and zygomatico-facial vessels are controlled, and the lateral orbital rim is carefully removed. Then, with the protection of periorbita with a malleable retractor, the lateral orbital wall (greater wing of sphenoid) is removed utilizing a high-speed drill. This exposes the lateral orbit till the region of orbital apex.
Total lateral orbitotomy
In this extended lateral orbitotomy approach, the bone flap is extended to encompass the superior orbital rim up to the supra-orbital notch. Inferiorly, the bone flap extends across the body of zygoma till the mid-point of the inferior orbital rim. Removal of the superior orbital rim and the orbital plate can provide access to the anterior cranial fossa also through this approach. Although this approach provides a very good exposure to the orbit, it is associated with an unsightly surgical scar and cosmetic deformity in the lateral orbital wall. A total lateral orbitotomy, therefore, is reserved for extensive orbital lesions extending into the orbital apex, the superior and inferior orbital fissures, and the pterygopalatine fossa.
Modified lateral orbitotomy
It is a minimally invasive variant of the classical lateral orbitotomy performed without severing the lateral canthal ligaments, and a tangential trajectory is used to expose the greater wing of the sphenoid, and if needed, the region near stem of Sylvian fissure, anterior cavernous sinus, and adjacent cisterns.[32] In this approach, a small (approximately 15 mm) lateral orbital rim is removed, followed by elevation of the periosteum and adjacent temporalis muscle. Two cuts are made in the lateral orbital rim, one at the level of body of zygoma and another just below the fronto-zygomatic suture. After this, the anterior part of greater wing of sphenoid can be drilled if the exposure of temporal dura mater is needed.
Fronto-temporal craniotomy with/without orbito-zygomatic osteotomy
The fronto-temporal or pterional craniotomy is the most common surgical approach used by neurosurgeons to access the region of orbital apex. This approach provides good visualization of the postero-lateral portion of posterior orbit. It also provides an easy access to the anterior temporal region, the superior orbital fissure region, and the optic canal (after clinoidectomy). This approach is usually centered on the Sylvian fissure and exposes the lesser wing of the sphenoid bone (sphenoid ridge). The fronto-temporal/pterional approach and its modification is often associated with partial atrophy of the temporalis muscle and an associated depression in the temporal region. Thus, these extensive trans-cranial approaches are mainly for tumors involving the orbital apex and for tumors having an intra-cranial extension. [22]
An orbito-zygomatic modification using a single piece or a two-piece craniotomy further increases access to the superior orbit, and to the medial aspect of middle cranial fossa up to the region of the inter-peduncular cistern. This approach can be used for extensive lesions involving the orbital apex, anterior, and middle cranial fossa, as well as the para-sellar and basilar apex region.
The mini-pterional approach
First described by Figueiredo et al., this modification of the pterional approach utilizes an accurately placed scalp incision over the region of sphenoid ridge (commencing 1 cm above the zygomatic arch and ending at the mid-pupillary line). This approach has been proven to be comparable to the conventional pterional approach in terms of surgical exposure.[36]
Lateral supra-orbital approach and supra-orbital keyhole approach
The lateral supra-orbital approach was initially popularized for lesions over the orbital plate (lateral anterior cranial fossa base) and for parasellar lesions by Jane et al.[37] This approach can be used to expose intra-orbital, extra-dural (intra-cranial) pathologies. It has also been utilized for sub-arachnoid space exposure in the region of the chiasmatic cistern (including the approach for anterior communicating artery aneurysms). In the traditional supra-orbital approach, a pterional-type scalp incision is made. Unless one is careful during the dissection, there is risk of injury to the frontal branch of the facial nerve, as well as associated soft tissue injury.
In the supra-orbital keyhole approach (SOKHA) variant, first described by Perneczky et al., a small incision is made over the lateral 2/3rd of the eyebrow, extending just short of the supra-orbital neuro-vascular bundle.[38] With meticulous dissection of the orbicularis oculi muscle, the lateral 2/3rd of the supra-orbital region is exposed preserving the periosteum, which is sharply divided and elevated. Following this, the frontozygomatic suture is identified and a key burr hole is made, and a lateral supra-orbital craniotomy is fashioned. Orbital plate of the frontal bone needs to be drilled to gain further access to the orbit. Frontal sinus, if exposed, needs to be exteriorized at this step. The SOKHA can be safely used with/without endoscopic assistance for various anterior cranial fossa neoplastic entities and for anterior circulation aneurysms.[39]
The limitation of this approach, however, is the restriction of maneuverability, potential scarring in the region of eyebrow, as well as exposure of the frontal sinus and its related complications of infection or mucocoele formation.
Endoscopic endonasal approach
The endoscopic endonasal approaches (EEA), including the extended endoscopic approaches to the orbit, are gradually evolving and replacing the microsurgical approaches to the orbit, especially for medially located lesions. The main advantage of the EEA is its anterior and medial trajectory, which is particularly suitable for tumors located antero-medial to critical neuro-vascular structures and optic nerve, displacing them supero-laterally.[40] EEA is also the procedure of choice for lesions involving the medial orbit and extending into the adjacent ethmoidal air cells. Successful performance of the medial intraconal EEA on 6 patients was reported by Kibwei et al., in 2011 and interest in this approach and related published literature has been on the rise.[41],[42],[43]
The principles for EEA are: (i) Crossing the optic nerve should be avoided; (ii) the entry through the lamina papyracea should be below the level of the ethmoidal foramina to avoid injury to the ethmoid arteries that can lead to retro-bulbar hematoma and vision loss; and, (iii) dissection should be done between the muscle groups rather than through individual muscles to preserve function. “Plane of resectability” (POR) as described by Banks et al., is an imaginary plane joining the contralateral nostril and the long axis of the optic nerve [Figure 11]. Lesions that are medial to the optic nerve or below the POR are particularly suitable for EEA. [43, 44] Contrarily, tumors that are lateral to the optic nerve or superior to the POR are not candidates for pure EEA.[10] The added illuminance and magnified view provided by the EEA is a boon for medially located intraconal tumors. The exposure of region in traditional approaches is through a narrow deep cone-shaped surgical corridor. However, the lack of depth perception and three-dimensional perception can be disorienting for the surgeon especially in the early part of learning curve. | Figure 11: Landmarks determining feasibility of endoscopic endonasal approach to the orbit have been shown in this coronal T1 contrast MRI at the level of posterior orbit. The plane of resectability (POR) is an imaginary plane joining the inferior edge of the optic nerve sheath and the contralateral nostril (green dashed line); and, another vertical plane medial to optic nerve sheath is drawn (blue dashed line). Tumors located below the POR (green shaded area) and medial to the optic nerve sheath (blue shaded area) can be candidates for exclusive endoscopic resection.[43]
Click here to view |
The three main types of endonasal approach to the orbit include:
- The medial-inferior extraconal approach,
- The trans-maxillary approach, and,
- The medial intraconal approach
All endonasal approaches essentially have similar initial phases, including an uncinectomy, a wide maxillary antrostomy, along with anterior and posterior ethmoidectomies and sphenoidotomy, aimed to expose the medial and inferior orbital walls. The most often used scope is the 0-degree scope; however, the 45-degree scope is required for adequate visualization of the orbital apex region, especially within the muscle cone. A uni-nostril approach can be used for small extraconal tumors; however, a bi-nostril approach is often favored for intraconal lesions/large lesions or lesions near the orbital apex, as the latter provides significantly better maneuverability and a good visualization. The complete exposure constitutes a medial-inferior extraconal approach.
The trans-maxillary approach adds an extra medial maxillectomy anteriorly to expose the entire orbital floor. Through this approach, the entire inferior orbit as well as the maxillary antrum, and if needed, through the posterior wall of the maxillary antrum, the pterygo-maxillary fissure region and even the middle cranial fossa, can be exposed. The medial intraconal approach is used for medial-inferior and posterior intraconal lesions. This utilizes the corridor between the medial and inferior recti and has a much better access than the traditional medial micro-orbitotomy approach. For intraconal exposure, the periorbita is incised parallel to the medial rectus muscle and the muscle cone is gently dissected. The recti are retracted carefully using vessel loops and the orbital fat is warded off gently using a cotton tipped applicator. Retraction of the globe anteriorly, thus retracting the recti from the orbital opening side, can help in dissection. This can be done by an ophthalmological surgeon.
| Complication avoidance | | |
Visual deterioration
Respecting tissue planes; avoiding crossing the optic nerve during surgery through the retrobulbar fat; and, a copious saline irrigation (to avoid heat related optic nerve injury) during careful drilling of roof of the optic canal using a diamond drill avoids this compication [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16] | Figure 12: a: A lady with left eye proptosis. b and c: Coronal, and d: Parasagittal images showing left eye proptosis due to the orbital plate meningioma pressing on the globe. The frontal craniotomy and excision of the meningioma brought about lasting relief in the patient
Click here to view |
 | Figure 13: a and b: Basal axial CT scan images showing the infiltrative lesion of the optic nerve in a small child causing proptosis and loss of vision indicative of a round cell malignancy. The child had unilateral corneal ulceration and proptosis. c and d: The axial CT images of the brain also show the infiltrative lesion continuing to form a suprasellar mass with gross hydrocephalus. The child underwent an ultrasound guided biopsy of the orbital lesion followed by radio-and chemotherapy.
Click here to view |
 | Figure 14: Coronal image showing an optic nerve sheath meningioma with the tram-track sign.
Click here to view |
 | Figure 15: a: Axial CT scan; and, b: Axial, and c: Parasagittal MRI images showing a cavernous hemangioma with a well defined plane of cleavage located medial to the optic nerve. d: Removal of the hemangioma using the subfrontal approach
Click here to view |
 | Figure 16: a: Coronal MRI showing a superomedially located cavernous hemangioma, b: operated using the endonasal endoscopic approach
Click here to view |
Retrobulbar hematoma
A meticulous hemostasis and avoiding a blind dissection along the tumor capsule avoids this complication.
Cerebrospinal fluid rhinorrhoea
Meticulous dural repair of any dural injury of the frontal base; and occasionally, the placement of a peroperative lumbar cerebrospinal fluid drainage may avoid this complication, which usually results from opening of the frontal or ethmoidal sinuses
Orbital infection or meningitis
Infection of the orbital contents is always a possibility when there is a breach of asepsis. If the frontal sinus exposure is required, it should be optimally managed by removal of its mucosa (to avoid the formation of a mucocoele); plugging the cavity with muscle graft; and, exteriorization of the sinus opening using a pedicled pericranial graft.
Postoperative diplopia
This may occur either due to postoperative edema of the soft tissue or due to entrapment of ocular muscles during reconstruction of the orbit. In the intraconal region, the occurrence of any extra-ocular nerve injury may also result in this complication, so dissection of the tumor has to be meticulous, respecting tissue planes. The ciliary ganglion (into which the parasympathetic fibres relay and the sympathetic fibres pass through) and the nerves arising from it are positioned lateral to the optic nerve. In the orbital apex region, nerves to the extra-ocular muscles also lie lateral to the optic nerve. Therefore, an approach medial to the optic nerve is usually preferred.
| Conclusion | | |
With the ever-increasing armamentarium of surgical approaches, a complete “round the clock” approach to the orbit is feasible with minimal/acceptable morbidity. A neurosurgeon ready to manage orbital tumors needs to be well versed with these approaches as well as the intricacy of the orbital anatomy to tailor-adopt the appropriate approach for a particular orbital lesion. This may often need teamwork and may include an ophthalmological surgeon or a colleagues from otorhinolaryngology.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16]
[Table 1], [Table 2], [Table 3], [Table 4]
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