Endoscopic Repair of a Medial Orbital Wall Facture With the “Milan Technique”
Endoscopic Medial Orbital Wall Reconstruction After Removal of an Orbital Mass Via a Transnasal Approach
Among the seven bones composing the orbit, the maxillary bone and the ethmoid bone represent the thinnest boundaries. Therefore blunt trauma to the orbit most often results in inferior and/or medial wall fractures rather than lateral wall and orbital roof injuries. More specifically, the lamina papyracea of the ethmoid bone, aptly named because of its extreme frailty, composes most of the medial orbital wall, which makes medial wall fractures very common.
Medial and inferior orbital wall fractures do not necessarily have absolute surgical indications (small, isolated blow-out medial wall fractures generally might not require treatment, although late enophthalmos can become an aesthetic concern for such patients ). However, complications are very likely to occur with fractures exceeding 1 cm 2 or 50% of the wall. Furthermore, extrinsic orbital muscle impinging in the fracture margins, thereby inducing ophthalmoplegia and subsequent diplopia, represents another general indication for medial and inferior orbital wall fractures repair.
There is an intrinsic technical challenge associated with orbital fracture surgery, as well as some risk of complications in restoring the orbital rim and in functionally reconstructing the globe, the extraocular muscles, the lacrimal system, and other structures. The optic nerve, the extrinsic muscles, and the lacrimal system can be hindered by even minor mistakes, with predictable dire consequences. Furthermore, the complex anatomy and a constrained surgical filed sometimes make exposing the structures and correcting defects with implants a significant challenge.
Several traditional open surgical accesses to the orbit have been proposed over the course of many years to provide the best exposition of tissues coupled with minimal invasiveness and optimal aesthetic outcomes. The anterior half of the orbit is managed through a group of incision collectively designated as anterior orbitotomy, with the incision located according to the orbital quadrant requiring intervention. Access to the orbit is gained either subperiosteally (via the orbital rim) or orbitally (via the orbital septum) approach. The orbital rim can be reached with incisions, including direct brow, subbrow, Lynch, inferior rim, Kronlein, subciliary, subtarsal, and transconjunctival, with or without lateral canthotomy. None of these approaches is risk free, and poor cosmetic or functional outcomes have led to abandoning some of these procedures. The historic (and still valid from a tissue exposition standpoint) Lynch incision, for example, provides excellent exposure to the medial orbit at the cost of medial canthal web formation, a visible scar, and potential medial canthal malpositioning, whereas subciliary approaches allow broad access to the orbital floor but can cause lower lid retraction and malposition. The latter approaches grant only limited access to the medial wall. Transconjunctival incision might allow lower morbidity than cutaneous incisions (although this was not scientifically proven) and was originally described in 1924; it is mostly used to access the orbital floor.
Although the anterior, inferior, and medial orbit are easily managed with these accesses, the lateral and posterior orbit, as well as the orbital roof, require more complex strategies, such as lateral orbitotomy to access the lateral orbit and the retrobulbar space, with lateral canthotomy or extended eyelid crease skin incision as the most common procedures, with possible implementation of neurosurgical approaches, such as coronal incision or fronto-orbito-zygomatic cranio-orbitotomy. These complex approaches entail significant operative and recovery time and neurosurgical-related morbidity.
Endoscopy in orbital surgery presents, as in other surgical fields, the opportunity to couple extensive surgical field vision with minimally invasive approaches. The first attempt in endoscopically accessing the orbit dates back to the early 1980s with the work of Norris and Cleasby, furthered by Braunstein and colleagues research in the mid-1990s. These techniques initially failed to allow a safe and expandable cavity for surgery. With the wide diffusion of endoscopic surgery in otolaryngology in the late 1990s, transnasal and transantral endoscopic orbital surgery gradually became a surgical tool for maxillofacial surgeons, otolaryngologists, and ophthalmologists. Currently the application of endoscopic techniques to orbital fracture repair allows complete exposition of fractures, regardless of depth, and incarcerates tissues, encouraging accurate implant placement and reducing injuries to noble orbital structures with marginal invasiveness.
This chapter focuses on the treatment of medial orbital wall fractures, with special emphasis on transnasal endoscopic approaches, which allow for excellent functional and esthetic results while completely avoiding problems related to external approaches. The last section of the chapter provides useful information on managing complex fractures with the aid of endoscopy and on using endoscopy as a tool for addressing the management of complex orbital fractures.
Medial Orbital Wall Fractures
The medial orbital wall, as the locus minoris resistentiae, is the second most frequently injured orbital boundary after blunt trauma. As covered further in the chapter, medial orbital wall fractures can also present concomitant orbital floor fractures in a more complex scenario.
Two different etiopathogenic theories have been suggested as an explanation for medial orbital blow-out fractures: the hydraulic theory and the buckling theory. According to the first paradigm, intraorbital pressure becomes elevated owing to retropulsion of the orbit; such elevated pressure leads to fracturing the medial orbital wall in the point of lowest resistance. The latter paradigm links medial orbital wall breaches to a direct trauma involving the medial orbital rim. Independent of the physiopathogenic mechanism, any blunt trauma involving the eyeball and/or the medial orbital rim can lead to a fracture of the lamina papyracea, causing herniation of the medial orbital content into the nasal cavity. This means that not only the fatty orbital content, but also the muscles can enter the nasal cavity with a nonnegligible chance of muscular entrapment; again, enophthalmos and/or diplopia may follow.
From an anatomic standpoint, it is worth remembering that the medial orbital wall is formed not only by the lamina papyracea (which almost inevitably is fractured), but also by the lacrimal bone anteriorly, the maxillary bone inferiorly, and the lesser wing of the sphenoid posteriorly. A suture runs at the border between the ethmoid and the frontal bone, in close proximity to the anterior and posterior ethmoidal arteries. This suture represents the closest point to the dura and thus should be approached with the utmost attention to avoid cerebrospinal fluid leaks. Ethmoidal arteries can allow for an average estimate of the anteroposterior orbital depth, given that the anterior ethmoidal artery runs 24 mm from the lacrimal crest, whereas the posterior ethmoidal artery lies 12 mm posterior to this and the orbital apex 6 mm further posteriorly.
As mentioned earlier, both fat and muscle (more specifically, the medial rectus muscle) can herniate toward the nasal cavity; therefore, indications for medial orbital wall repair are diplopia and significant enophthalmos. Although evaluating gaze in all position is always recommended because the medial rectus muscle is usually affected, the horizontal gaze should be given the maximum attention during evaluation to identify the slightest restrictions. Although clinically relevant enophthalmos, as well as diplopia, are generally appreciable with a careful clinical examination, a CT scan is mandatory to provide information on the fracture site, the number of fragments, and anatomic relationships. This is especially relevant if a pure transnasal endoscopic access is planned, which must rely on the usual landmarks of endoscopic sinus surgery to avoid damage to noble structures. Furthermore, the CT scan provides information on the size of the fracture, allowing for proper planning. Mirrored CT images coupled with neuronavigation enable also more precise orbital reconstructions.
Medial wall fractures have been approached historically in countless ways. The first reliable proposal was the Lynch incision, ultimately abandoned because of poor overall aesthetic results. Currently the approaches to medial wall usually rely on transconjunctival accesses, including the transcaruncular, precaruncular, and retrocaruncular routes. All these accesses usually couple swift direct access to the fracture site with an acceptable surgical field. Nevertheless, these approaches are hampered by very limited visibility of the posterior and superior areas of the medial wall and by potential injuries to the lacrimal sac and to the lower oblique muscle. The need for eyeball manipulation is another disadvantage, though minor, in these approaches. To overcome these disadvantages, many authors have relied on endoscopy, which has been used as an aid to traditional approaches or in completely new ways through the transnasal route.
Many recently introduced techniques saw a tight collaboration among ophthalmologists, maxillofacial surgeons, and otolaryngologists. Most of these techniques have been developed to address both tumors and orbital fractures, with a specific focus on the posteriormost areas—the orbital apex and the periorbital skull base—which are the areas least easily exposed through external approaches. Excellent case series have been published (e.g., Murchison et al. ). In this series a multidisciplinary team (neurosurgeon, otolaryngologist, and orbital surgeon) performed ethmoidectomy, sphenoidotomy, and posterior lamina papyracea removal to enter the orbit in 18 patients with a range of pathologies including cavernous hemangiomas, juvenile angiofibromas, and invasive cutaneous squamous cell carcinoma. Approaching these lesions somehow led the way to approaching with a higher degree of safety, smaller, localized lesions, such as medial wall fractures. In these regards, it may be worth noting that in these case series, complications were relatively common (22% of the patients) and included decreased postoperative visual acuity and cerebrospinal fluid leak. Although the extent of exposition for approaching medial wall fractures is considerably more limited, the orbital surgeon should never forget that the orbit should always be regarded as a high-risk location.
Other interesting case series on endoscopic approaches were published by Chhabra et al. and Bleier et al. These two articles report a detailed experience in treating orbital venous malformations (commonly misnamed as cavernous hemangiomas ), a condition that frequently requires extensive dissection, removal of the papyracea, and extrinsic orbital muscle dissection. The experience with these patients not only strengthened the anatomic knowledge of the medial orbital wall from an endoscopic perspective but also added information on an important feature common to medial orbital wall—that is, the enophthalmos caused by the herniation of orbital content toward the nasal cavity. Although modern views on these techniques state that minimally invasive accesses do not tend to induce enophthalmos, the same approach we describe in detail for medial orbital wall fractures could be adopted to reconstruct the medial orbital wall after endoscopic orbital mass removal.
Restricting once again the focus on endoscopic reconstruction of medial orbital wall fractures, it is worth noting that the transnasal-transethmoidal and transcaruncular approaches and conjunctival incisions are the most commonly used approaches and both grant the avoidance skin incisions and optimization of cosmesis. Among the first notable case series was the one from Hinohira et al., who performed a transnasal endoscopic medial wall reconstruction on 23 patients with isolated medial blowout fractures with a 95.5% success rate. When using the transnasal approach, nevertheless, most authors usually rely on supporting the medial wall with a silicone sheet and/or using additional long-term nasal packing to contain the herniated orbital content, with obvious patient discomfort and a theoretical increased risk of infection. Conversely, the use of other materials such as high-density porous polyethylene with an endoscopic transcaruncular approach (which means an external approach aided by the endoscope, not a pure endoscopic approach) showed excellent results with minimal discomfort.
The Milan Approach to Medial Wall Orbital Fractures
Our group developed the so-called Milan technique for medial orbital walls fracture repairs. The technique combines the expositional advantages offered by the transnasal endoscopic approach and the effectiveness of reconstruction with stable porous polyethylene implants. This endoscopic transnasal technique has an excellent success rate, requires no packing or prolonged hospital stays, and has proved its efficacy—even in the long term—in a considerably sized patient group.
This technique can be applied to any patient with medial wall fractures dating back no more than 15 days who have enophthalmos and/or extrinsic orbital muscle movement impairment. A preoperative CT scan is required to measure the expected lamina papyracea defect and to identify the anatomic landmarks. The CT scan further allows quantification of the enophthalmos and identifies whether fat tissue alone or fat and muscle are herniating into the nasal cavity. We do not rely on any intraoperative navigation for fracture repair purposes.
With the Milan technique, surgery begins by placing the patient in the standard position for endoscopic sinus surgery; both eyes must be visible in the operating field. After nasal mucosa decongestion, the procedure is started with a 0-degree scope; uncinectomy, middle antrostomy, and radical ethmoidectomy are performed in the affected side to approach the lamina papyracea and expose the orbital floor. Although the use of powered instruments (debriders and such) can be considered, we prefer to exert extreme care while approaching the fractured lamina papyracea, removing the ethmoid bone with cutting forceps and grasping forceps, avoiding powered instruments. Because such patients usually do not have a nasal inflammatory condition, bleeding is most often minimal. The swollen mucosa must be distinguished from the herniated orbital content and removed carefully to minimize the risk for postoperative mucoceles. All the fractured fragments of the lamina papyracea must then be removed to avoid pushing them back in the orbit at the time of positioning the reconstructive sheet. After removing all mucosa and fractured bone fragments, constant landmarks can be identified; anteriorly, superiorly, and inferiorly it must be possible to identify the healthy, solid margins of the medial wall. In this maneuver a 45-degree scope can assist the surgeon in visualizing the margins. The posterior aspect of the fracture is typically shaped as an acute angle connecting the upper and lower margins. With the aid of a ruler (usually a flexible disposable ruler), the anteroposterior size of the defect is measured and a 0.8-mm thick porous high-density polyethylene sheet is shaped accordingly, exceeding the measured defect by few millimeters both in length and height.
The shape of the prosthesis should be shaped as a guitar pick, with a medial concavity, going toward the orbit. The polyethylene prosthesis is placed over the herniated content and gently pushed laterally into the orbit until entering the fracture margins. A curved instrument (suction tip or such) can be used to aid positioning the sheet inside the fracture margins. After it is placed inside the fractured margins, the sheet becomes then self-containing, impinging on the fracture margins (this requires a precise shaping of the implant itself by the surgeon). No stenting, packing, or prosthesis covering is required. We advise intraoperative antibiotic prophylaxis and obtaining a postoperative CT scan 24 to 48 hours after the procedure to confirm the correct reconstruction. Figs. 33.1 to 33.4 show a typical case of medial orbital wall fracture addressed with this technique.