The endoscopic transnasal approach to the orbit usually starts with complete sphenoethmoidectomy and wide opening of the maxillary ostium to oversee the orbital floor. Then the papyraceus lamina is identified and resected, and the periobit is opened to gain access to the intraorbital space. To facilitate identification of the lamina, the periorbit, or the tumor at a later stage, a simple trick is to exert gentle pressure to the eyeball to push and medialize the orbital wall or content. An alternative to that approach was proposed by Shah et al. to avoid moving one hand of the surgeon out of the field or require an assistant to push the globe. With this technique a blunt instrument is used to apply pressure to the expected location of the papyraceus lamina. If the lamina has been adequately exposed, the whole lamina will be seen moving. If residual ethmoid lamellae are attached, no movement or partial movement can be seen. Theses first steps can easily be accomplished with 0-degree endoscopes. When intraorbital pathology is addressed, angulated scopes (e.g., 30-degree or 45-degree) may help to increase visualization of the surgical field because the optical angle becomes wider the more lateral one dissects. Sometimes a partial septectomy or a septal window is helpful to approach the orbit from both nasal cavities and through both nostrils, especially in a four-handed technique. With the advent of three-dimensional (3D) endoscopy, spatial orientation may be enhanced, especially when targeting the orbital apex and skull base. In particular, the approach to the intraconal space harbors two major sources of difficulties for visualization and localization of pathology: the protruding orbital fat and the extraocular muscles. Contrary to orbital decompression, when protrusion of orbital fat and decrease of intraorbital pressure is desired, here it hampers the view and working space if intraorbital lesions, predominantly tumors, are addressed. Because of the mass effect of the tumor, intraorbital pressure is elevated, promoting the protrusion of fat after incision of the periorbit. However, it is advised not to remove the fat to maintain normal eyeball movement and ocular muscle function and to avoid enophthalmos postoperatively. Therefore incision through the periorbit should be limited before the ethmoidectomy has been completed to avoid obstruction of the surgical field. The fat should be dissected bluntly with standard instruments such as elevators or dissectors until the tumor capsule is identified. It is also helpful to use cottonoids or cotton-tipped applicators to gently dissect the connective tissue and spread the fat out of the way. Here, tactile feedback is very important, and advanced endoscopic techniques such as 3D endoscopy may not be as helpful as in fixed structures such as the skull base, because the fat is constantly manipulated and changes its orientation in space. Moreover, the endoscope lens could be obstructed more easily when closer to the fat and intraorbital space, which would additionally be of disadvantage for the 3D effect. In general—as in all endoscopic approaches—a clear field and endoscope lens is of utmost importance. Classically antifog solutions of different preparations and patties or small beakers are used to keep the lens clean. Automated self-cleaning devices for the scopes are beneficial to avoid frequent egress of the endoscope for extra nasal cleaning. Here the endoscope is put into an extra shaft that is linked to an irrigation device and pump and can be flushed on demand by operating a foot petal. The only disadvantage may be that the endoscope’s working diameter is increased owing to the extra shaft, which could hamper movement of instruments in narrow spaces and corridors (e.g.. if the nostrils are tight).
Handling of Bleeding During Surgery to Improve Visualisation
If bleeding occurs during the dissection, it can usually be handled with swabs soaked in adrenaline 1:1.000. When using adrenaline, however, vasospasms to the centralis retinae and ciliares posteriores arteries may occur. Distinct arterial bleeders may be cauterized with bipolar devices if properly identified. When the superior/medial compartment needs to be addressed, the ethmoidal arteries may be in the surgical field. In particular, the anterior ethmoidal artery can be identified on computed tomography by looking for a pyramidal notch at the papyraceus lamina between the superior oblique and medial rectus muscles. This notch marks the exit of the artery from the orbit. If it is likely to be crossed during the intraorbital approach, it can be dissected and ligated easiest by bipolar cautery forceps. Care is needed to cauterize the entire intranasal length of the artery and dissect it in the middle to avoid retraction and intraorbital bleeding. If the notch cannot be seen on CT, the artery runs in the skull base. If it needs to be crossed to gain access superiorly, the skull base must be thinned out carefully with a diamond burr to expose the artery and cauterize it thereafter. The same can be done for the posterior ethmoidal artery, especially for posterior lesions close to or in the orbital apex. However, extensive cauterization of the orbital fat should be avoided for the same reason as not resecting it. Furthermore, the nerves and muscles can be endangered by excessive cautery. Other hemostatic agents such as Oxicell (Apex Energetics, Irvine, CA), TachoSil Fibrin Sealant Patch (Johnson & Johnson Ethicon, Bridgewater, NJ), or Floseal (Baxter International, Deerfield, IL) may be applied. Oxicell and TachoSil are helpful after surgery to avoid minor oozing; however, intraoperative use of Floseal is suitable because it can be easily suctioned away once the bleeding stops and would not obstruct the view or access. Oxicell also expands and hardens when soaked with blood; thus it should not be left/put intraorbitally but may be placed over the orbital fat or remaining periorbit. Fibrin glue—particularly, autologous fibrin glue—can be sprayed into the cavity to prevent oozing and to seal the orbit. However, postoperative infection of the orbit is very rare and orbital reconstruction is rarely necessary.
Adjuncts for Intraorbital Tumor Dissection
Once the tumor is identified, extracapsular dissection may be facilitated by enlarging the incision of the periorbit. The tumor itself can be cauterized to reduce its volume and facilitate dissection and removal. An alternative to cautery may be cryoassisted tumor ablation as described by Campbell et al. and Castelnuovo et al. Here, once the lesion is exposed medial and inferior, a cryoprobe (modified ophthalmic standard cryoprobe) is placed in contact with the capsule of the tumor and activated, which creates temporary adhesion owing to the so-called Joule-Thompson effect. Once the probe is activated, freezing temperatures are reached at its tip and the tissue becomes frozen white, which proofs the adherence of the tumor and its capsule to the probe. Care is needed to avoid freezing of surrounding structures. When adhesion of the lesion is achieved, it can be manipulated by gentle torsional traction to separate it from surrounding connective tissue. This process can be repeated to achieve extracapsular dissection, and the lesion can subsequently be pulled out of the orbit, which makes further dissection and visualization easier.
For intraconal tumors, another obstacle toward the anticipated lesion is the medial rectus muscle. Damage to it may lead to severe diplopia, and restoring the muscle after iatrogenic dissection is challenging, if not impossible.
Dealing With Extraconal Muscles
A simple technique to avoid damage to the muscle and keeping it out of the visual field is a temporary medialization through sutures or slings. Here the muscle is identified before entering the intraconal space, and a suture or vessel loop is placed around the muscle. Thereafter it can be gently pulled out of the field and be positioned as desired ( Fig. 10.1 ). Monofilic, larger-diameter sutures (e.g., 2-0) should be used to decrease trauma to the muscle tissue and its delicate capsule. After completion of the surgery, the suture is removed. In addition, a trocar can be inserted via the canine fossa to provide a third corridor for instruments or scopes and thus gain space and better angulation intranasally ( Fig. 10.2 ).