9.1 Introduction

Transnasal endoscopic approaches have added tremendously to our ability to treat midline skull base lesions in the pediatric population. From the crista galli to the upper cervical spine, we are now able to address many lesions that until recently would have required an open surgical approach. Though often effective, traditional open approaches create a significant amount of collateral damage and morbidity that should be avoided if possible.

While transnasal corridors are highly effective to approach the majority of midline skull base lesions, in some cases the pathology is obstructed by the orbits or may actually involve the orbital bone or contents. Given their position occupying much of the anterior cranial fossa (ACF) and anterior aspect of the middle cranial fossa (MCF), the orbits block much of the transnasal corridor to these regions.

Rather than being considered an obstacle to be avoided, the orbits might be looked at as large potential portals to the ACF, MCF, and adjacent structures. With this possibility in mind, over a decade ago we began looking into whether endoscopic pathways within and through the orbit could serve as alternative or adjunct routes to targets that were challenging to reach through nasal portals. ¹ We found that through four transorbital endoscopic approaches that can be used in monoportal or multiportal technique, ^{2 ,​ 3 ,​ 4 ,​ 5} we can expand our endoscopic armamentarium to access the majority of skull base pathology involving or adjacent to the orbit. ^{6 ,​ 7} This chapter will describe our current concept of a quadrant-centered model of transorbital endoscopic skull base surgery.

9.2 Terminology

Endoscopic surgery of the orbit can be divided into two primary types: transorbital and transnasal. The former includes transcutaneous and transconjunctival portals that provide direct entrance into the orbit. The latter refers to corridors that proceed through a naris, the ethmoid sinuses and lamina papyracea to enter the medial orbit, or through the maxillary sinus to enter the medial orbital floor. It is also possible to enter the orbit using a portal in the face of the maxillary sinus, traveling through the maxillary sinus to enter the floor of the orbit, though monoportal transmaxillary orbital approaches are uncommonly used for tumor surgery.

Within the realm of transorbital approaches, there are four primary portals, one for each quadrant (superior, medial, inferior, and lateral). These approaches can be used for surgery within the orbit (endoscopic orbital surgery); for pathways through the orbit to adjacent targets (transorbital endoscopic surgery); or for pathways through the orbit to neurologic targets (transorbital neuroendoscopic surgery [TONES]). For these procedures, we use the term “pathway” to connote a surgical route through a volume that is created by dissection, in distinction to “corridor,” which suggests a preexisting space such as the nasal cavity through which access is achieved. We do not consider these procedures to be “minimally invasive,” as invasiveness is dictated by the nature and location of the pathology rather than the approach. However, these procedures are “minimally disruptive,” in that they minimize collateral damage to tissue that is not involved in the disease process, thereby creating the least possible morbidity and allowing the swiftest possible return to previous lifestyle.

9.3 Experience and Outcomes in Transorbital Surgery

There have been multiple reports on experience with transorbital surgery, and these are appearing with increasing frequency and with perspectives from international sources. These approaches have been described for the treatment of skull base tumors, ^{8 ,​ 9 ,​ 10} infectious processes such as epidural abscess and sinogenic pathology, ¹¹ cerebrospinal fluid (CSF) leak repair, ¹² cavernous sinus pathology, ¹³ seizure disorders, ¹⁴ ethmoid artery ligation for control of epistaxis, and trauma surgery ¹⁵ through endoscopic and robotic techniques. ⁴

The surgical outcomes with transorbital procedures have been highly favorable. In an early report of our initial outcomes with transorbital endoscopic procedures on over 100 patients, we found no complications due to the surgical approach, and had a high success rate in achieving the surgical goals. Our results in the 5 years since that publication have been similarly favorable.

The morbidity that patients experience postoperatively depends on the orbital quadrant involved, as well as the extent of the pathology and duration of surgery. Temporary ptosis is expected with superior quadrant pathology due to retraction of the levator muscle, as is forehead numbness from retraction of the supraorbital and supratrochlear nerves. If these nerves are preserved, sensation is expected to return. Likewise, temporary diplopia is not uncommon after surgery in any of the four quadrants, due to retraction of the extraocular muscles that is required to access and treat the surgical target. Postoperative pain from the surgical approach is typically minimal: when a transorbital portal is combined with a transnasal approach, in our experience, patients typically report less pain from the orbital component of the surgery. Given that the alternative to these approaches is in many instances bifrontal or other open craniotomy, we believe that these techniques constitute truly minimally disruptive surgery.

Our experience with pediatric applications of these procedures has also been excellent. Pathology, including trauma (brain, dural, orbital, and frontal sinus injury), tumors (esthesioneuroblastoma, juvenile nasopharyngeal angiofibroma [JNA], neuroma, orbital osteoma with extension into the brain), orbital lymphatic malformation, and complications of sinogenic pathology involving the orbit and skull base have been favorably addressed in the pediatric population. We have performed tumor excisions, including resectioning of the skull base and orbital bone in patients as young as 18 months of age without adverse outcomes. Though there remain few reports in the literature of the use of these procedures in the pediatric population, based on our favorable experience to date we believe that cautious use of transorbital surgery in the pediatric population is safe when used appropriately, particularly when faced with the alternative of open craniotomy.

9.4 Indications and Contraindications

Transorbital endoscopic approaches are indicated for benign or malignant lesions of similar pathology and extent to those that are treated with a transnasal approach. The decision to use a transorbital endoscopic approach must be based on the location, extent, and characteristics of the pathology. Major considerations are whether the pathology could be treated by an endoscopic approach, and whether the safety of adjacent critical neurovascular structures can be ensured. For larger tumors invading the orbital contents that require exenteration, transorbital endoscopic technique can be quite useful. Endoscopic enucleation can be performed, after which there is a wide field for any further endoscopic resection that might be required, such as a tumor invading the frontal lobe of the brain. For appropriate defects, transorbital endoscopy can be combined with endoscopic brow lift portals for multiportal harvest of a vascularized pericranial flap.

Transorbital procedures are contraindicated in patients who have had recent orbital trauma with hyphema or globe rupture. These procedures should be undertaken with caution in patients who have had ocular surgery within the last 6 months, recent orbital infection, significant inflammatory disease, or loss of corneal sensation. ⁷

9.5 Issues Peculiar to Pediatric versus Adult Skull Base Surgery

Endoscopic skull base surgery in pediatrics deserves special attention due to the age and stages of craniofacial development of the patients. Preoperative planning is essential in both the pediatric and adult populations. The limited volume of the nasal cavity and under-pneumatized sphenoid sinus in younger children impairs the use of the four-handed endoscopic and microsurgical technique used for endoscopic endonasal approach (EEA) to skull base pathology. In addition, the intercarotid distance (ICD) has been shown to be significantly more narrow in the 2- to 4-year-old range and progressively widens with age as the sphenoid becomes pneumatized. ¹⁶ This pneumatization is usually completed by the age of 16 years. However, most pediatric patients are divided into the less-than – 11-year-old and the greater-than – 11-year-old categories when addressing the access of the EEA. A conchal sphenoid is associated with a narrow ICD and therefore should be strongly considered prior to EEA. An ICD of 10 mm is recommended prior to considering an EEA for intradural pathology.

The delayed pneumatization of the frontal sinus, however, expands the opportunities for the supraorbital keyhole craniotomy via an eyebrow incision as either a single approach or used as an operative and endoscopic port.

The volume of the nasal cavity in the pediatric patient is a significant concern when addressing complex and highly vascular lesions of the skull base. The smaller working area causes the “coning down” of instruments and more instrument “sword fighting” (▶ Fig. 9.11). This is most apparent as surgeons address clival and more lateral pathology. The pediatric population has a decreased blood volume as compared to an adult and therefore the minimization of blood loss is even more crucial, thereby raising the importance of a four-handed endoscopic and microsurgical technique. The dual-portal approach, TONES combined with an EEA, affords improved visualization and increased degrees of instrument working room when an endoscopic transsphenoidal or transclival approach is utilized. ¹⁷ While the utilization of this approach is too limited to quote outcome data, it has been studied in a simulated real-time adult cadaver vascular perfusion model. Utilizing a dual or multiportal approach may be considered to address these complex lesions.

The growth centers or suture lines along these portal pathways should be evaluated prior to surgery. The avoidance of suture line disruption should be considered. A medial TONES approach via a pre-or transcaruncular approach to the central skull base may be safer, as the surgeon remains below the frontoethmoidal suture. Similarly, the same approach to the subfrontal region can be achieved by staying above the frontoethmoidal suture. There are not enough outcome data at this time to further assist in the decision-making process; however, this may serve as a guide. Delaying surgery until the patient matures should be considered to avoid the risks of growth-plate disruption. However, this may not be feasible, given that most pathology needs to be addressed. There are potential advantages to adding a port, and therefore it should not be dismissed but rather considered carefully.

A special consideration in the pediatric population is the effect of surgery on the developing craniofacial skeleton. Specific to the maxillary sinus, the biggest risk is a hypoplastic maxillary sinus. This does not typically result in maxillary retrusion or maxillary deficiency as seen in certain craniofacial syndromes with midface deficiency (e.g., Crouzon’s syndrome), but it may have long-term implications if the patient develops chronic sinusitis. Indeed, studies have shown that the most consistent factor to alter the maxillary sinus volume is prior Caldwell–Luc procedure. ¹⁸ However, many of the alternative surgical approach options for surgical targets in these regions incur even more morbidity, such as a Le Fort I osteotomy or a craniotomy. Thus, despite the risk for decreased maxillary sinus volume, if it permits adequate access to a lesion that would otherwise require an approach with more morbidity, it should be strongly considered with adequate patient and patient-family counseling.

A child’s ability to cooperate and follow guidance is also important postoperatively. Cases of children with hyperactivity disorders can at times make their care highly challenging.

9.6 Anatomy

The anatomy of the eyelids and their support structures dictates the location and geometry of the portals that are created for transorbital endoscopy; deeper anatomy of the orbital bone and adjacent orbital structures influences the pathways and optical chambers that are created.

The eyelids consist of skin, orbicularis oculi muscle, and, deep to that, the orbital septum. The septum is a continuation of the periosteum of the orbital rim. Deep to the septum is located the eyelid support system (▶ Fig. 9.1).

The primary support consists of the superior tarsus and inferior tarsus, the superior tarsus being supported by the levator muscle and aponeurosis, and the inferior tarsus being stabilized by the lower lid retractors. A critical difference between the upper and lower lids is that the lower lid retractors can be transected without deleterious effect, while the upper lid levator system must be preserved to prevent severe ptosis. As a result, we can perform a transconjunctival lower lid approach, but the upper lid approach must be transcutaneous. Also important in eyelid support are the medial canthus, which surrounds the lacrimal system, and the lateral canthus. The lateral canthus can be separated and detached from the orbital rim (canthotomy and cantholysis) as long as it is reconstructed at the end of the procedure. The medial canthal tendon cannot be transected without damage to the lacrimal system, and must therefore be preserved. The medial canthal tendon attaches to the anterior and posterior limbs of the lacrimal crest, enveloping the lacrimal sac. The lateral canthal tendon attaches 1 to 2 mm posterior to the anterior aspect of the orbital rim, inferior to the frontozygomatic suture.

For endoscopic surgery, the orbit is divided conceptually into superior, medial, inferior, and lateral quadrants by intervening structures that must be preserved. Each quadrant is entered through a unique portal (orbitotomy). The trochlea of the superior oblique muscle separates the superior from the medial quadrant; the insertion of the inferior oblique muscle demarcates the medial and inferior quadrants. The inferior and lateral quadrants are separated by the contents of the inferior fissure, while the superior fissure separates the lateral and the superior quadrants (▶ Fig. 9.1; ▶ Fig. 9.2).

Once the orbitotomy is created and the pathway is established, the subperiosteal dissection within the orbit can be widened to cross quadrants. This is not the case with all portals, however; the superior transcutaneous portal cannot be connected with the transconjunctival medial portal.

The key anatomic structures of the superior approach include the lacrimal gland laterally, and the trochlea medially. These structures can be elevated off the orbital bone in the subperiosteal plane. Dissecting posteriorly along the roof, there are no obstacles until the orbital apex is reached. Medially, the optic nerve is approached where it enters the orbit through the posterior medial wall. Laterally, the anterior aspect of the superior fissure is encountered.

For the medial dissection, key structures to be aware of include the posterior limb of the medial canthal tendon, which is visualized immediately deep to the incision. This structure is followed posteriorly to the posterior lacrimal crest, where the subperiosteal plane is entered. Dissecting posteriorly, the ethmoid arteries are encountered at the junction of the orbital roof and medial wall. These (typically three or more) are cauterized with bipolar forceps sequentially, dissecting posteriorly until the optic nerve is encountered. ¹⁹ The bone of the medial wall, the lamina papyracea, is extremely thin and must be handled delicately if it is to be preserved. Inadvertent fracture of the bone can cause minor bleeding from the underlying mucosa, which subsides spontaneously.

The inferior approach proceeds directly through the conjunctiva of the inferior fornix, through a small amount of fat, and then to the subperiosteal plane at the inferior orbital rim. Further posteriorly, the inferior fissure is located at the lateral floor. Some fibrous tissue, small vessels, and the zygomatic (sensory) nerve traverse the inferior fissure, and can be transected without notable deficits. The inferior fissure courses posteriorly and medially, where deep to the periosteum it joins the superior fissure (▶ Fig. 9.2).

The lateral approach can be accessed through a retrocanthal transconjunctival portal, or a canthotomy and cantholysis can be added to the dissection. The subperiosteal plane is entered, and dissection continues posteriorly. In the anterior orbit, the dissection can be extended to the orbital roof or floor. More posteriorly, however, the fascia of the superior and inferior fissures become the boundaries of the dissection, converging to meet at the posterior orbit. As noted, the contents of the superior fissure must be preserved, while the structures of the inferior fissure can be cauterized and divided. Meticulous hemostasis in this region is critical.

9.7 Choice of Approach

Accurate surgical approach selection for access to skull base pathology is critical for successful outcomes. The approach (or approaches) dictates the incurred morbidity and collateral tissue damage, and the ability to perform the surgical task required at the target site, whether that be obtaining a tissue sample for biopsy or complete resection and reconstruction. The optimal surgical approach maximizes visualization and instrumentation at the target site, yet minimizes collateral tissue damage. As mentioned earlier, the term “minimally invasive” is a misnomer as the degree of “invasive” is determined by the pathology, and it is our job to determine an approach that offers adequate access to pathology while minimizing damage to collateral tissue in the process. We promote the term “minimally disruptive.”

In an ideal case, the surgical pathway is direct, short, and has geometric boundaries that are just large enough to permit adequate instrumentation. Depending on the surgical task, fundamental minimum dimensions of the surgical pathway are required. For example, if endoscopic visualization with a 4-mm endoscope, plus one instrument (pituitary forceps) is required to perform a biopsy at a skull base location, then the initial surgical pathway shape must meet the minimum dimensions to permit the 4-mm-diameter endoscope working in concert with pituitary forceps. In this instance, the dimension at the midpoint (center of instrument angulation) must be 9 mm in the typical biconical shape (4-mm diameter of endoscope + 4-mm diameter of pituitary forceps + 1-mm clearance). The biconical shape is hypothesized to be the ideal endoscopic surgical pathway because it permits adequate instrument angulation. This was demonstrated in an engineering optimization study gaining access to the lateral cavernous sinus through a lateral retrocanthal approach. Prior to iterative computer analysis, the proposed surgical pathway was the same width throughout the length, but with computer planning and dimension optimization at the center point of instrument angulation, the volume of the pathway reduced by 27% without compromising visualization and instrumentation at the target site. The size of the craniotomy in the MCF (middle cranial fossa) was also reduced by 48%, and thus the collateral tissue damage was reduced (▶ Fig. 9.3; ▶ Fig. 9.4). ¹³

In addition to instrument range of motion within the pathway, the angle of approach to a given pathology significantly impacts the ability to safely perform surgical tasks at the target site. Indeed, with greater than 20 endoscopic surgical approaches described through the craniofacial skeleton to access the skull base, there is a wide range of approach angles available to the surgeon. One specific example where approach angle becomes critical is in the region of the optic canal. In this instance, dissection from a perspective that is near parallel to the nerve has distinct advantages over an approach that is near-perpendicular. A near-parallel approach offers the surgeon an optimal endoscopic view to remove thinned bone along the optic nerve because the nerve is visualized along its length during bone removal. Thus, selecting the surgical approach angle may have a high priority for addressing specific pathology, and it may be that a surgical pathway that is longer, but has a better approach angle, provides the best overall access.

In the multiportal approach, the angle of the two (or more) portals relative to each other is important. These angles determine how two or more instruments will work in concert, and it determines the viewing angle. In endoscopic sinus surgery, it is routine that a single instrument works through the same portal as endoscope, and the two are nearly parallel. These are advantageous in the ability to instrument at the target site when the angulation is widened. It allows for reproduction of standard microsurgical techniques where multiple instruments are working in concert providing retraction and maintaining tension on the tissue that is being dissected or divided. Current surgical robotic platforms have limitations on the angle, and most require at least 20° between them to work effectively without collision.

Finally, a major factor to consider in the selection of a surgical approach is the degree of instrumentation required at the target site, and the number of simultaneous instruments required in addition to an endoscope. In the literature, the optimal endoscopic skull base surgery is done in a “four-handed” technique with two surgeons working together, each with two instruments. Perhaps a more accurate determination to make is not the number of instruments or hands required, but rather the number of functions needed, such as ablation, irrigation, suction, cautery, and navigation. The number of functions is a more relevant number because an increase in the functions may not result in an increase in the number of surgical portals. It is acceptable, and in fact better if the same surgical effect can be achieved with fewer instruments. Many advanced instruments now have multiple functions. For example, an ultrasonic bone aspirator provides multiple functions, including ablation, irrigation, and suction. A Coblator provides suction, irrigation, and radiofrequency ablation and hemostasis. As technology emerges that continues to combine functions, it may reduce the need for either additional surgical pathways or wider dimensions for any given pathway.

The selection of a pathway requires many considerations, including visualization, instrumentation, pathology type and location, and individual anatomy, but selected pathways should be as close to ideal as possible in order to maximize the surgical effect while minimizing collateral tissue damage.

9.8 Transorbital Approaches

The approach is determined by the quadrant of the orbit that is occupied by the pathology or that the path to the pathology will traverse (▶ Fig. 9.5).

Once the quadrant of the orbit is noted that involves or provides access to the pathology, the type of incision to enter that quadrant is decided upon. While there are some variations in the exact placement of the incision, the primary incisions and access techniques used for each quadrant will be described below.

Before making the incision, the patient is given appropriate antibiotics and, unless contraindicated, 8 to 10 mg of dexamethasone. The size and shape of the pupils at the beginning of the case is noted. If desired, exophthalmometry can be performed with the patient asleep to aid in deciding on reconstructive options at the end of the procedure. A temporary tarsorrhaphy is typically placed at the lateral limbus bilaterally, allowing the lids to be opened to monitor the shape and size of the pupils. Ophthalmic lubricant is placed and maintained throughout the case. During the operation, the ipsilateral pupil is regularly checked for any change in shape or size, either of which can indicate excessive pressure on the globe or other orbital contents. This is particularly important when dissecting behind the equator of the globe toward the orbital apex. If this occurs, retractors and instruments are removed from the globe until the pupils become symmetric. While a corneal protector may give the surgeon added comfort, if one is used it needs to be removed frequently to check the pupils.

Retraction of the orbital contents is performed with malleable brain retractors. Care is taken not to angle the distal end of the retractor into the orbital contents, but rather to gently distract the contents with even pressure along the retractor. A thin sheet of Silastic can be placed between the orbital contents and retractor to aid in both retraction and maintaining a patent optical cavity.

9.8.1 Superior Quadrant

The superior quadrant lies between the lacrimal gland laterally and the trochlea of the superior oblique muscle medially. A transcutaneous blepharoplasty incision is used for this approach (▶ Fig. 9.6), placed in a dominant crease of the upper eyelid skin. The incision is typically 3 to 4 cm wide, and extends through the orbicularis oculi muscle. Dissection continues toward the superior orbital rim following the undersurface of the muscle, superficial to the orbital septum. This plane lies superficial to the prelevator fat. Once the orbital rim is encountered, the supraorbital and supratrochlear neurovascular bundles are located and preserved. In some cases, these run through a palpable notch in the orbital rim which can aid in their location. The periosteum of the superior orbital rim is then incised and lifted off the bone with a periosteal elevator, creating a plane into which the orbit is entered inferior to the bone of the orbital roof and superior to the orbital periosteum (periorbital). The plane is developed posteriorly to a depth of approximately 1 cm, at which time a 0-degree endoscope is introduced and dissection continues under endoscopic visualization. A suction Freer elevator is useful for the dissection that, though largely bloodless, is helpful when a small amount of bleeding is encountered. Any blood vessels extending through the periorbital into the bone can be ligated with bipolar cautery. Dissection then continues, exposing the region of the orbit or adjacent orbital roof that is needed. If a craniotomy is performed for transorbital access to the frontal lobe, this is done with a diamond burr or ultrasonic bone aspirator. If entry into the frontal sinus is desired, the entry point is determined by navigation guidance, and the bone is taken down in a similar fashion. If dissection to the orbital apex is required, as the posterior limit of the orbital roof is encountered, navigation is checked to ascertain the exact position of the optic nerve and superior orbital fissure, both of which are bounded by periosteum. If access to the brain is desired, the position of the dural opening is confirmed by navigation, and the incision in the dura is made in standard fashion. Once the procedure is completed, the reconstruction is completed as noted below.

Related posts:

2 Pediatric Rhinologic Considerations 4 Patient Positioning and Operating Room Setup 8 Combined Transcranial and Endonasal Approaches 5 Instrumentation 10 Endonasal versus Supraorbital Eyebrow Approaches: Decision-Making in the Pediatric Population 7 Endonasal Corridors and Approaches

Stay updated, free articles. Join our Telegram channel

Join