Endoscopic orbital decompression of complications of thyroid-related orbitopathy
Graves’ disease is an autoimmune disorder affecting the thyroid, orbit and skin. Approximately 50% of patients with this disorder develop orbital manifestation of dysthyroid orbitopathy. Fewer than 5% of such patients have disease that is severe enough to require surgical decompression of the orbit (Metson and Samaha, 2004). The extensive muscle enlargement limits globe movement in extremes of gaze which will cause diplopia. Visual loss in Grave’s disease is uncommon, occurring in only 2 to 7% of patients (Kountantakis et al, 2000; Kuppersmith et al, 1997). Exopthalmos in Grave’s disease is thought to result from the deposition of immune complexes in the intraocular mucles and fat which in turn leads to edema and fibrosis (Tandon et al, 1994). The resultant increase in intraorbital pressure pushes the globe forward causing proptosis. If this proptosis become severe enough, the eyelids cannot close properly and chemosis with or without exposure keratitis of the cornea may occur. Furthermore, the crowding of the orbital apex by the obviously enlarged extraocular muscles places pressure on the optic nerve. Stretching of the optic nerve by increasing proptosis may result in the development of optic neuropathy and visual loss. If medical treatment fails (high dose steroids with or without low-dose radiotherapy) , surgical decompression of eyelid is indicated(Cook et al, 1996).
Removing one or more of the bony walls can decompress the contents of the orbit. The least amount of decompression would be achieved with medial wall removal, but the most physiologic and least to cause complications like globe displacement and diplopia. Endoscopic orbital decompression affords maximal orbital decompression at the orbital apex, an area that is not fully accessible via the external or transantral routes (Metson et al, 1994). Many techniques have been described for decompressing the orbit but the order of the procedures is that orbital decompression first, then strabismus and lastly the eyelid.
Indications and contraindications
The primary indication for the surgery is exopthalmos, either for cosmetic reasons or when vision is deteriorating and steroids and radiotherapy treatment has failed. The most common indications for such surgery are exposure keratopathy and optic neuropathy that have been refractory to conservative measures. Patients with diplopia from dysthyroid orbitopathy may require decompression before strabismus surgery to reaccess the globe and improve the predictability of muscle adjustments. Some surgeons who consider aesthetically undesirable proptosis to be an indication for orbital decompression have performed such surgery for its cosmetic benefits.
Contraindications to endoscopic orbital decompression include acute sinusitis and anatomic abnormalities of the maxillary bone. Endoscopic decompression may be technically difficult in patients with very small maxillay sinuses or thick orbital walls. These features are easily identified on computed tomography (CT) scan of the orbit and sinuses, which should be obtained on all patients before surgery.
Endoscopic orbital decompression