Abstract
For more than 100 years, surgical decompression of the orbit has been used to treat severe proptosis and thyroid eye disease, also known as Graves ophthalmopathy. With the advent of endoscopic sinus surgery in the mid-1980s, otolaryngologists began experimenting with endoscopic orbital surgery, with the first descriptions by Kennedy et al. and Michel et al. arriving soon thereafter in the early 1990s. With enhanced visualization and improvement in instrumentation, safe and thorough decompression of the medial orbital wall and orbital floor can be achieved without external approaches. An excellent understanding of sinonasal anatomy and landmarks, as well as proficiency with endoscopic sinus surgery, is a prerequisite for performing this procedure safely. Moreover, a team-based approach with ophthalmology will not only strengthen the otolaryngologist’s ability to perform this procedure safely but also know the limitations of this approach and when it is appropriate to combine this approach with a lateral or superior decompression. Endoscopic orbital decompression also provides a stepping stone for the skills required to perform transnasal endoscopic orbital surgery in the appropriate setting, as well as an understanding of the complications related to endoscopic orbital surgery and appropriate management strategies.
Keywords
endoscopic, Graves disease, ophthalmopathy, orbital decompression, proptosis, thyroid eye disease
Introduction
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For more than 100 years, surgical decompression of the orbit has been used to treat severe proptosis and optic neuropathy associated with Graves disease, also known as Thyroid Eye Disease (TED).
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Although decompression techniques involving removal of each of the four walls of the orbit had been described, the transantral approach reported by Walsh and Ogura in the 1950s had been favored by most otolaryngologists.
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Soon after the introduction of transnasal endoscopic sinus surgery in the mid-1980s, surgeons began to experiment with endoscopic orbital surgery.
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Endoscopic orbital decompression was first described by Kennedy et al. and Michel et al. in the early 1990s.
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The enhanced visualization of key anatomic landmarks permits safe and thorough decompression of the entire medial orbital wall and the medial portion of the orbital floor.
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This improved visualization is most notable in the region of the orbital apex, a critical area of decompression in patients with optic neuropathy and a region poorly visualized with conventional external approaches.
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These marked advantages have allowed the endoscopic approach to replace previously described techniques as the technique of choice for orbital decompression.
Anatomy
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Anatomy is best addressed in relation to the individual sinuses and is important to identify on preoperative imaging ( Fig. 18.1 ). The orange shading in Fig. 18.1 indicates the structures removed as part of an endoscopic orbital decompression.
Fig. 18.1
Schematic drawings in coronal (A) and axial (B) view showing the boundaries of endoscopic orbital decompression. Boundaries are for a standard endoscopic medial and inferior floor decompression; the area to be resected is shaded in yellow. n., Nerve.
Maxillary Sinus Landmarks
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The maxillary line corresponds to the junction of the uncinate process and the maxilla.
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The maxillary sinus roof (orbital floor) is an important landmark because it is a boundary of decompression.
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The infraorbital nerve courses through the maxillary roof and innervates the lower lid, the upper lip, and a portion of the vestibule (V2 distribution).
Ethmoid Sinus Landmarks
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The skull base is known to have a variable vertical height with an anterior to posterior downward slope.
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The posterior skull base meets the anterior face of the sphenoid sinus where it is relatively thick.
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The angle created at the junction of the sphenoid face and posterior skull base creates the sphenoethmoid angle, which represents the posterior limit of orbital decompression.
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The lamina papyracea is the thin orbital plate of the ethmoid bone, which forms the medial wall of the orbit that is removed during decompression surgery.
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In patients with TED, the lamina papyracea often has a bowed or convex appearance secondary to increased intraorbital pressures.
Sphenoid Sinus Landmarks
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Important sphenoid sinus landmarks include the following:
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The sphenoid face
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The superior turbinate, because the ostium is medial and inferior to this landmark
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The sphenoid ostium
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Preoperative Considerations
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Endoscopic orbital decompression is indicated for patients with moderate to severe symptoms of Graves orbitopathy, commonly known as Thyroid Eye Disease (TED). These indications include exophthalmos (including for cosmesis), exposure keratopathy, diplopia, and optic neuropathy.
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Endoscopic orbital decompression is also used to gain access to the orbit for the removal of benign orbital tumors, decompression of orbital abscesses and hematomas, biopsy of indeterminate lesions, palliative therapy for malignant tumors causing visual symptoms, transnasal endoscopic intraorbital ligation of the anterior ethmoid artery, and as the approach for optic nerve decompression.
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The endoscopic technique allows unmatched visualization of critical anatomic landmarks, including the skull base and orbital apex, while avoiding external or sublabial incisions.
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The procedure is usually performed under general anesthesia; however, local anesthesia with sedation can be used in patients with significant medical comorbidities or for surgery on a patient’s only seeing eye (depending on surgeon preference).
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Endoscopic orbital decompression may be performed unilaterally, bilaterally, or in a staged fashion and can be combined with lateral decompression.
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The risks, benefits, and alternatives should be discussed with the patient and ophthalmology team, but performance of bilateral decompressions as a single-setting procedure is generally recommended.
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Common practice is to perform endoscopic orbital decompression in a patient’s only seeing eye under general anesthesia.
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For severe disease, the recommended procedure is a balanced three-wall decompression, which combines an endoscopic medial wall and medial orbital floor decompression with an external-approach lateral wall decompression via lateral cathotomy.
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It is imperative to discuss the nuances of endoscopic orbital decompression with the anesthesia team preoperatively. This will limit potential aggressive postextubation bag-mask ventilation, which can result in subcutaneous and/or orbital emphysema.
Radiographic Considerations: Computed Tomography Checklist
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Evaluate the skull base orientation.
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Examine the middle turbinate attachment.
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Identify the location and course of the anterior ethmoid artery.
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Evaluate for the presence of an Onodi cell, or sphenoethmoid air cell—a posterior ethmoid cell that is positioned superolateral to the sphenoid sinus.
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The existence of an Onodi cell is important because the optic nerve can often course through the lateral aspect of this cell instead of through the sphenoid sinus proper.
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Suspect an Onodi cell when a four-quadrant sphenoid sinus is observed on coronal computed tomographic (CT) views, although this is best evaluated on sagittal CT imaging.
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Identify the location of the anterior ethmoid artery to prevent inadvertent injury intraoperatively.
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On coronal CT, the most posterior view of the globe demonstrates the anterior ethmoid artery within its canal as a nippling at the confluence of the medial rectus and superior oblique muscles.
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The artery is particularly at risk when a prominent supraorbital cell is present and the artery is located below the level of the skull base, within the ethmoid sinus.
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Evaluate the middle turbinate for the presence of a concha bullosa and note the attachment to the skull base.
Instrumentation ( Fig. 18.2 )
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Standard endoscopic sinus surgery set used to perform standard maxillary antrostomy, sphenoethmoidectomy, and middle turbinectomy
Fig. 18.2
Photographs of instruments used for endoscopic orbital decompression. Top, Ninety-degree curette, straight curette, and Cottle elevator. Bottom, Arachnoid knife and sickle knife.
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0-degree and 30-degree rigid nasal endoscopes
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Image guidance system—recommended but not required
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Key instrumentation for the decompression portion of the procedure:
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Sickle or arachnoid knife
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Cottle elevator
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Straight through-cutting forceps
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90-degree curette
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