Technique for Endoscopic Orbital Decompression
Andrew P. Lane
INTRODUCTION
Graves disease is an autoimmune thyroid condition that is frequently associated with a progressive inflammatory process of the orbit. While the majority of cases of dysthyroid orbitopathy can be successfully managed medically, surgical decompression may be necessary when the orbital manifestations cannot be controlled. First described over a half a century ago, transantral removal of the medial and inferior walls of the orbit had been the preferred otolaryngologic approach until the introduction of endoscopic techniques in the early 1990s. In more recent years, advances in endoscopic sinus surgery and related technologies have made endoscopic orbital decompression the most widely accepted and used approach. The light and magnification provided by sinonasal endoscopes allow excellent visualization of the critical anatomy, and current instrumentation permits precise and complete removal of orbital bone, while simultaneously preserving function of the paranasal sinus.
Optimal care of the patient with dysthyroid orbitopathy requires coordination between the ophthalmologist and the otolaryngologist. In the most severe cases of proptosis, a combined three-wall approach with a lateral orbitotomy and removal of orbital adipose tissue may be indicated. Even when an endoscopic technique is used, secondary ophthalmologic procedures may be required to correct strabismus or address eyelid retraction to achieve a superior final result. The endoscopic surgeon must be meticulous and knowledgeable about the anatomy of the patient’s sinuses in order to avoid delayed complications secondary to sinus outflow obstruction or damage to adjacent structures.
HISTORY
Graves ophthalmopathy occurs most often in middle-aged women and is the most common cause of unilateral or bilateral proptosis in adults. Patients may present at various stages of the disease and may display signs of hyperthyroidism such as weight loss, sweating, palpitations, and feeling warm. Typically, patients requiring orbital decompression will be referred from an ophthalmologist to the otolaryngologist for consideration of surgery after the thyroid disease has burned out or has been managed. The clinical manifestations of dysthyroid orbitopathy vary widely in type and severity. The most minor eye changes include conjunctival injection or chemosis, dryness, and tearing. Inflammation of the orbital tissue in the confined space of the bony orbit can result in the classic exophthalmos that typifies thyroid eye disease. The proptosis can be cosmetically problematic in and of itself, or it can lead directly to further complications such as exposure keratopathy, diplopia, and visual loss secondary to optic neuropathy. In many cases, compression of the optic nerve in the orbital apex occurs without prominent proptosis, particularly when the inflammation is more prominent in the extraocular muscles than in the orbital adipose tissue. Surgery is not needed for limited symptoms, which usually can be improved with application of eye lubrication or closing the eye with tape or a patch. For more significant symptoms, including visual loss, patients may benefit from systemic corticosteroids, but the response is usually transient. Radiation of the orbit may be helpful when the disease is in an active state with acute visual changes.
PHYSICAL EXAMINATION
External orbital manifestations are evident on general physical inspection. The otolaryngologic examination focuses on the nasal endoscopy. Attention must be paid to anatomic variations that might impact exposure of the medial wall of the orbit. Deviation of the nasal septum, concha bullosa, and paradoxical middle turbinates should be noted. In addition, the presence of inflammatory disease within the nasal cavity or middle meatus should alert the surgeon to the need for aggressive preoperative medical therapy to optimize postoperative healing. It is important that visual parameters and measurements of proptosis be documented prior to surgery.
INDICATIONS
Indications for endoscopic decompression of the orbit include (1) exophthalmos, which may cause disfigurement or be complicated by corneal exposure keratopathy; (2) compressive optic neuropathy with visual impairment; (3) discomfort due to orbital pressure or pain; or (4) orbital congestion. As the morbidity of the endoscopic approach is minimal, orbital decompression for cosmesis may be considered in some patients.
In the setting of compressive optic neuropathy with threatened visual loss, emergent posterior endoscopic decompression of the orbit may be indicated. However, concomitant treatment with systemic steroids often alleviates or slows the progression of visual loss, thus reducing the urgency of the procedure. Endoscopic decompression of the orbit may be relatively contraindicated in patients who are generally poor surgical candidates, and in this case, radiation therapy and immunosuppressive agents may be used in an attempt to avoid surgery altogether.
CONTRAINDICATIONS
There are no absolute contraindications to endoscopic decompression of the orbit; however, any comorbidity that increases the risk of general anesthesia must be weighed against the benefit of the surgery. The patient should be euthyroid prior to consideration of surgical intervention with general anesthesia, although this may not be possible in the context of progressive visual loss due to optic nerve compression. The use of medications and health supplements that inhibit blood clotting is a relative contraindication for endoscopic surgery, as bleeding will limit visualization and may result in postoperative hemorrhage. Chronic sinusitis should be optimized prior to surgery. Patients should be informed of the potential risks of surgery including visual loss, tearing, or diplopia.
PREOPERATIVE PLANNING
Imaging Studies
A high-resolution CT scan of the paranasal sinuses is essential for extended endoscopic endonasal approaches to adjacent anatomic structures such as the orbit. As with endoscopic sinus surgery, the surgeon should carefully review the CT to understand the anatomy and carry out preoperative planning. Attention should be paid to the shape of the nasal septum and the presence of anatomical variants including pneumatization of the orbital floor (Haller cells), sphenoethmoid cells (Onodi cells), and frontal cells. Recognition of asymmetries in the height of the ethmoid cavity and slope of the skull base will aid in safe identification of the fovea ethmoidalis during surgery. A specific concern is the relationship between the floor of the orbit and the superior margin of the inferior turbinate. For patients in whom the distance between the attachment of the inferior turbinate concha and the orbital floor is narrow, there is an increased risk for closure of the maxillary opening by prolapsed orbital adipose tissue and scarring. Also, the narrow window may limit access to the roof of the maxillary antrum to perform a complete decompression of the inferior wall. On the axial CT images, it is important to assess the orbital apex and its relationship to the anterior wall of the sphenoid. In most patients, the face of the sphenoid corresponds to the annulus of Zinn, and hence, only the optic nerve is contained within the sphenoid sinus, but in some cases, anterior pneumatization of the sinus can result in a portion of the posterior orbital apex being beyond the sphenoid anterior wall. This may be critically important when optic neuropathy is present. MRI is not necessary for preoperative planning in Graves disease but may be useful to define the soft tissue anatomy when performing orbital decompressions for intraorbital tumors or other inflammatory lesions.
SURGICAL TECHNIQUE
The procedure of endoscopic orbital decompression may be performed to address the medial wall only or both the medial and inferior walls, depending on the indications for surgery and the extent of decompression desired. In either case, the surgery is initiated in the same fashion as is endoscopic sinus surgery. The mucosa in the nasal
cavity is decongested topically with cotton pledgets soaked in a vasoconstrictive agent such as oxymetazoline (0.05%). The nasal septum is assessed, and an endoscopic septoplasty is performed if necessary to allow wide access to the middle meatus. Next, injections are performed in the lateral nasal wall with 1% lidocaine with 1:100,000 units of epinephrine. A spinal needle or a tonsil needle may be used to reach the region of the sphenopalatine foramen, where sufficient injection should be performed to see a blanching of the lateral wall and inferior aspect of the middle turbinate. Alternatively, an intraoral injection via the greater palatine foramen may be performed to decrease blood flow through the sphenopalatine vessels into the nose. An additional injection is performed at the anterior insertion of the middle turbinate, with a second injection more inferiorly on the turbinate if sufficient blanching is not observed. The middle meatus is then further decongested with either oxymetazoline or 4% cocaine solution on a cotton pledget for at least 5 minutes. During this interval, registration of a computer-assisted surgical navigation system can be accomplished, if one is to be used.
cavity is decongested topically with cotton pledgets soaked in a vasoconstrictive agent such as oxymetazoline (0.05%). The nasal septum is assessed, and an endoscopic septoplasty is performed if necessary to allow wide access to the middle meatus. Next, injections are performed in the lateral nasal wall with 1% lidocaine with 1:100,000 units of epinephrine. A spinal needle or a tonsil needle may be used to reach the region of the sphenopalatine foramen, where sufficient injection should be performed to see a blanching of the lateral wall and inferior aspect of the middle turbinate. Alternatively, an intraoral injection via the greater palatine foramen may be performed to decrease blood flow through the sphenopalatine vessels into the nose. An additional injection is performed at the anterior insertion of the middle turbinate, with a second injection more inferiorly on the turbinate if sufficient blanching is not observed. The middle meatus is then further decongested with either oxymetazoline or 4% cocaine solution on a cotton pledget for at least 5 minutes. During this interval, registration of a computer-assisted surgical navigation system can be accomplished, if one is to be used.
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