The development of transnasal endoscopic approaches to skull base pathology significantly decreased the surgical disruption and collateral damage relative to their open predecessors, such as the craniofacial and subcranial approaches. In addition, the improved illumination, magnification, and visualization on a high-quality monitor afforded by endoscopes provided surgeons with major technologic improvements.
Although transnasal approaches are the most common endoscopic pathways in use today, drawbacks to these procedures remain largely because of the presence of the orbits. The orbits occupy approximately 80% of the anterior cranial fossa (ACF) and a significant portion of the middle cranial fossa (MCF). They obstruct transnasal access to these locations or force the use of angled endoscopy and instrumentation. Another drawback to transnasal approaches is the narrow funnel effect —again, because of obstruction by the orbits—in which access to the ACF narrows significantly in the superior aspects, making simultaneous visualization and instrumentation a challenge. In addition, when accessing the ACF, particularly intracranially, it is necessary to approach with upward angulation and then progress parallel to the floor of ACF. We refer to this as the attic effect —when the surgeon is required to reach up into another space and work within that plane. The opposite of this is when the surgeon can visualize and use instruments in the same plane as the entry portal, or what we call coplanar surgery.
In 2005, we began to investigate whether the orbit could be transformed from an obstruction into a portal. The orbital bone is among the thinnest in the body; the orbit is adjacent to the paranasal sinuses (maxillary, ethmoid, sphenoid, and frontal). The roof of the orbit is composed of the ACF; the deep extension of the orbit abuts the MCF; and the lateral wall is adjacent to the infratemporal fossa (ITF) and MCF through the greater wing of the sphenoid. These observations suggested that the orbit could provide a direct pathway to these regions. After extensive study in the cadaver laboratory, we developed four primary routes to targets within the orbit and regions adjacent to the orbit ( Fig. 38.1 ). In 2010, we reported our initial clinical experience and outcomes using these approaches. In that consecutive series, all procedures were successfully achieved, and there were no complications related to the surgical approaches. We subsequently published multiple reports on further applications, experience, and outcomes using these procedures, the means of combining them with other approaches in multiportal technique ( Fig. 38.2 ), strategies for preoperative panning, techniques in reconstruction, feasibility for use in robotic surgery, and pediatric applications. Groups from Italy, South Africa, and the United States have added significantly to this literature.
We found that transorbital approaches allow ample access to targets without the narrow funnel effect. And because the entry portal and surgical target are usually with in the same plane, the attic effect is avoided and coplanar surgery is possible. By approaching targets from the orbit, endoscopic access to the ACF, MCF, and ITF is no longer obstructed.
As noted previously, numerous groups have also published their international experience with these procedures. In a particularly important work, Locatelli et al. published their experience as well as an excellent meta-analysis of the literature in 2016. They identified 38 clinical articles in the literature from 2010 to 2015, as well as multiple nonclinical studies, with no significant complications reported. They concluded that “transorbital endoscopic skull base surgery appears to be a safe and effective technique with complications lower than traditional external approaches and comparable with or even better than those published for transnasal or transmaxillary approaches.”
At the time of writing, a PubMed search of transorbital endoscopic procedures yielded more than 90 publications, and we are aware of others in press. Endoscopic orbital surgery has thus received a significant amount of attention given the relatively short duration of its use, with rapid adoption and highly favorable reports in the literature. This chapter outlines our techniques for endoscopic orbital and transorbital surgery, as well as our surgical outcomes, and provides references for further education.
Indications and Contraindications
Endoscopic orbital and transorbital surgery may be indicated to treat pathology involving the orbit and related structures, as well as structures adjacent to the orbit in the frontal sinus, ACF, and MCF. These approaches may be used alone, in multiportal combination with other approaches, or in hybrid techniques combining endoscopic and open approaches. At times we use these approaches bilaterally or approach a target from the contralateral side for improved approach and instrumentation angles.
We have treated patients ranging in age from 18 months to 92 years for a full range of pathologic conditions, including benign and malignant tumors, infection (epidural, orbital, sinogenic), vascular/hemorrhage, trauma, cerebrospinal fluid (CSF) leak, and endocrine disorders.
Contraindications to endoscopic orbital and transorbital procedures are somewhat theoretical at this point, given that relatively few complications have been reported in the literature. Primary concerns would be a history of recent ophthalmologic issues, such as a ruptured globe, hyphema, or infection. Relative contraindications would include a history of ocular surgery within the past 6 months, conditions of increased intraocular pressure (inflammatory processes), and prior LASIK surgery (a potential cause of decreased corneal sensation). These conditions, along with glaucoma or dry eye symptoms, should be evaluated by an ophthalmologist before proceeding with surgery.
Surgical Planning
Meticulous preoperative planning is critical in skull base surgery owing to the complexity of the anatomy, with multiple critical structures in highly close proximity encased in bone. Planning must include a global analysis of the pathology and its proximity to, or involvement of, adjacent structures. Once it is determined that a lesion can and should be resected, the ideal minimally disruptive technique is determined.
The choice of a surgical technique can be quite complex but may be simplified when broken down into its key components: the portal (an incision or natural orifice), the pathway (a dissection route within tissue planes or a preexisting corridor), and the target (the pathology). A portal should be created to prevent scarring or loss of function and to provide ample access to the pathway. A natural orifice such as a nostril can be excellent for this purpose. A pathway should provide the shortest possible distance from the portal to the target in the least disruptive manner possible. It must (1) allow the repeated passage of multiple instruments without the production of excessive secretions or blood and (2) provide adequate volume for an endoscope and/or instrument. In addition, reconstruction of the pathway, if needed, must be possible.
The type of instruments to be used is important in planning. Although it has been emphasized that four-handed surgery should be possible during a procedure, with contemporary instruments consideration of the number of functions required may be more important than the number of hands to activate them. For example, a surgical bone aspirator provides suction, irrigation, and ablation in one instrument. In addition to these functions, illumination and visualization (two functions provided by one instrument) are needed. Thus two instruments operated by two hands may provide five functions. Typically, we aim to perform four to six functions synchronously through a given pathway.
Additional factors important in the choice of pathway are the angles of approach, instrumentation, and visualization. Although angled endoscopy may provide the ability to view a target, available instrumentation may not be adequate for resection of a target that is poorly angled from the approach. The angle between instruments used simultaneously must also be sufficient to prevent collisions (approximately 18 degrees for pituitary surgery). Likewise, the volume of the approach must be adequate for the manipulation of instruments and endoscope, yet small enough that adjacent structures are not endangered (approximately 3 mL 3 ). The geometry of the pathway is also very important. As determined by digital tracking and analysis of instrument motion during endoscopic surgery, instruments may not pass from the portal to target in a linear fashion, but may actually traverse a biconical or other shape. The pathway shape must therefore allow the natural geometry of unimpeded instrument motion. Finally, the experience and abilities of the surgical team, as well as the desires of the patient, must be considered.
Surgical Technique
Detailed understanding of the anatomy of the orbit and structures contained therein (as outlined in Chapter 4 ) is critical before beginning to use these procedures. Key landmarks to consider are the location of the superior orbital fissure and the cranial nerves that traverse it; the inferior orbital fissure; the ethmoid neurovascular bundles marking the location of the base of the ACF; and the optic foramen. The fascial condensations that surround the orbital fissures and optic foramen are important in protecting these structures during endoscopic surgery within the orbit ( Fig. 38.3 ).
The patient is placed in the supine position, and general anesthesia is administered. The patient is given dexamethasone, appropriate antibiotic therapy, and for intracranial procedures acetazolamide may also be given. The head is rotated slightly toward the surgeon, and the neck is extended approximately 15 degrees to allow the brain to retract from the skull base if an intracranial procedure is anticipated. The head of the bed is elevated to minimize bleeding. The surgical navigation system is applied and registered, and accuracy is confirmed. Both eyes, the nose, and any other relevant anatomy are prepped and draped in the usual sterile fashion. The pupils are checked for baseline size and symmetry, the eyes are rinsed, and lubricant is applied. We do not typically use corneal protectors, as we regularly check the pupils for size, shape, and symmetry during the procedure. However, the use of corneal protectors may be desired until the surgeon has gained confidence with the procedures. Before beginning, surgical navigation is used to analyze the vector from the planned entry portal to the surgical target, and the appropriate surgical pathway is confirmed. The appearance of a typical approach is demonstrated in ( Fig. 38.4 ) The equipment is arranged as described earlier.
The basic instrumentation required is similar to that for other endoscopic skull base approaches. In addition, a Gorney suction elevator (JedMed), fine scissors (NovoSurgical), and range of malleable brain retractors (Millenium Surgical) are needed. Powered instrumentation, including an ultrasonic bone aspirator, may also be of use.
During surgery the pupils are monitored regularly for change in size or shape. There is no set frequency for doing this, but the deeper within the orbit the dissection proceeds, particularly as the optic nerve is approached, the more often the pupils are checked. If the pupil begins to dilate or change shape (such enlargement or the occurrence of an oval shape in the vector of globe displacement), the instruments are removed from the orbit until the baseline shape returns—usually a brief period. Care should be taken to provide the minimal amount of globe displacement necessary for the procedure, without undue pressure behind the equator of the globe.
Superior Approach
The superior approach provides access to the frontal sinus, ACF, and frontal lobe of the brain. This approach can be used unilaterally, bilaterally, or contralaterally as needed.
The superior approach is the only one of the four approaches that uses a skin incision, the same one used in upper blepharoplasty. A No. 15 blade or electrocautery on low voltage is used to make an incision in a dominant crease in the upper eye lid ( Fig. 38.5 ). The incision is typically 2 to 3 cm, depending on the location and depth of the pathology; the position of the incision is chosen by vector analysis with the navigation system. After incising the skin and orbicularis muscle, dissection continues superiorly toward the superior orbital rim in the suborbicularis (preseptal) plane, using a fine scissors. When the superior orbital rim is reached, the periosteum is incised with care taken not to injure the supraorbital and supratrochlear neurovascular pedicles. The periosteum is then raised and the subperiosteal plane is entered. Dissection proceeds posteriorly in the subperiosteal (subperiorbital) plane into the orbit using a malleable brain retractor to gently displace the orbital contents, and a suction Freer elevator is used to lift the periorbita from the bone (see Fig. 38.4 ). A layer of silastic or other pathway protector may be placed between the orbital contents and the malleable retractor. As dissection proceeds posteriorly, the ethmoid arteries will be encountered at the medial aspect where the orbital roof and lamina papyracea meet in the frontoethmoid suture. Following this suture posteriorly leads to the optic nerve, with the curvature of the orbit increasing as the apex is approached. As the orbital apex is approached, the superior orbital fissure will be encountered at the lateral extent, and medial to this the optic nerve is encountered. These structures are heavily invested in fascial condensation, which provides an element of protection during the dissection.
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