Endoscopic orbital decompression was developed soon after the advent of endoscopic sinus surgery. The technique was first described by Kennedy et al. in 1990 and Michel et al. in 1991 and has gained popularity over the past several decades, now representing about a quarter of orbital decompressions performed in the United States annually. The major advantages of the endoscopic approach include avoidance of an external facial incision and resultant scar, as well as improved visualization of key anatomic structures, particularly in the region of the orbital apex, a critical area of decompression in patients with optic neuropathy.
The major disadvantage of the procedure is coordination between an oculoplastic surgeon and an otolaryngologist and potential longer total operative time. Although no significant difference in cost of the procedure was observed with bivariate analysis, the need for coordination may contribute to the finding that the majority of oculoplastic surgeons surveyed perform the surgery alone via an external approach.
Graves orbitopathy occurs in up to half of patients with Graves disease and is the most common indication for endoscopic orbital decompression. Graves orbitopathy can be associated with visual deficits from optic neuropathy and diplopia. In patients with Graves disease, proptosis and exposure keratopathy are frequent indications for surgery. Graves orbitopathy, also known as thyroid eye disease (TED), is characterized by an initial acute inflammatory phase followed by a chronic, fibrotic phase. Typically decompression is performed in the chronic phase of TED; however, severe symptoms with optic neuropathy during the acute phase may warrant immediate treatment. Other indications for orbital decompression techniques include access for drainage of orbital hematoma or subperiosteal abscess, resection of orbital and intracranial pathology, and transnasal endoscopic intraorbital ligation of the anterior ethmoid artery.
Postoperatively patients undergoing endoscopic orbital decompression for TED reported significantly improved mean scores for the 22-item Sinonasal Outcomes Test from preoperative baseline after 1 year. When a Hertel exophthalmometer (Good-Lite, Elgin, IL) was used, a 3.2-mm reduction in proptosis was observed in patients with medial endoscopic decompression alone, with the addition of an external lateral decompression resulting in an additional 2.4-mm reduction in proptosis. Several studies have used preoperative and postoperative computed tomography imaging to quantitatively assess volume change after decompression. In one study of seven patients, an average increase in volume was 7.3 cm 3 in patients for whom medial and inferior orbital wall decompression was performed while maintaining an inferomedial strut. Another study, in which only medial decompression was performed, found an average increase in 6.08 cm 3 in volume on postoperative imaging of 12 patients.
Anatomy
Several key surgical landmarks are important to safely perform endoscopic orbital decompression ; these are listed in Box 20.1 . Fig. 20.1 illustrates the area of resection during an endoscopic orbital decompression. The lamina papyracea is the thin orbital plate of the ethmoid bone that forms the medial wall of the orbit that is removed during decompression surgery. It is often very attenuated, medially bowed, or even partially dehiscent in patients with Graves orbitopathy. The infraorbital nerve marks the lateral border of the inferior orbital wall (or floor), which is resected during an orbital decompression. The superior border of the medial wall decompression is defined by the skull base, frontal recess, and location of the anterior and posterior ethmoid arteries. The ethmoid skull base slopes downward in an antero-posterior vector and meets the anterior face of the sphenoid sinus posteriorly. This sphenoethmoid angle represents the posterior limit of orbital decompression.
Maxillary Sinus
- •
Maxillary line
- •
Uncinate process
- •
Nasolacrimal canal
- •
Infraorbital nerve
- •
Orbital floor–maxillary sinus roof
- •
Ethmoid Sinus
- •
Middle turbinate
- •
Skull base
- •
Lamina papyracea
- •
Anterior ethmoidal artery
- •
Sphenoethmoid cell (Onodi cell)
- •
Sphenoid Sinus
- •
Sphenoid face
- •
Internal carotid artery within carotid canal
- •
Optic nerve within optic canal
- •
Opticocarotid recess
- •
Appreciating the location of the medial rectus muscle within the surgical field is important to avoid injury and to create a periorbital sling if desired. The medial rectus is located reliably 1.5 cm above the crista ethmoidalis. Preoperative evaluation of imaging is critical when available to review the surgical landmarks and may be supplemented with intraoperative surgical navigation. Of particular importance is identification of sphenoethmoid (Onodi) cells as well as confirmation of the location of anterior and posterior ethmoid arteries and the opticocarotid recess when performing extended orbital procedures.
Technique
Unilateral or bilateral orbital decompression may be performed in a staged fashion or simultaneously on both eyes, depending on surgeon preference. For severe disease, consideration should be given to a balanced three-wall decompression, which combines an endoscopic medial and inferior floor decompression with an external-approach lateral wall decompression via lateral cathotomy. The patient is positioned in the typical fashion for endoscopic sinus surgery after general anesthesia is induced. The eyes are left in the surgical field and are protected with scleral shells or taping. Intranasal vasoconstriction is obtained with oxymetazoline or topical epinephrine-soaked pledgets and local anesthetic injection per the surgeon’s preference. Intraoperative image guidance decreases the risk of complications in endoscopic sinus surgery and should be used during endoscopic orbital decompression if available.
The first goal of the procedure is to obtain adequate visualization of the medial and inferior orbital walls for safe decompression. An uncinectomy is performed and a wide maxillary antrostomy is created to obtain adequate visualization of the posterior maxillary wall and orbital floor, as well as to avoid obstruction of the antrostomy by descendent orbital fat. Total sphenoethmoidectomy exposes the medial orbital wall, extending from the face of the sphenoid sinus down to the crista ethmoidalis and superiorly to the skull base. The middle turbinate may be resected for better visualization and postoperative monitoring. A good practice is to cauterize the posterolateral stump of the middle turbinate to prevent postoperative bleeding issues if the turbinate is resected. Mucosa over the medial orbital wall and medial floor is then removed often using an angled endoscope ( Fig. 20.2 ).
