Evolving Techniques of Orbital Decompression for Thyroid Orbitopathy

More surgeons are turning towards orbital decompression surgery as a means for addressing the severe disfigurement caused by thyroid orbitopathy (TRO), even when the disease is not vision threatening. This has occurred because of the improved safety profiles that have resulted from the modification of surgical techniques to successfully decrease postoperative complications in surgical decompression of the orbit. Specifically, many surgeons now accept the concept that in the presence of even small amounts of proptosis, eyelid malposition is better treated by decompression surgery rather than attempts to modify eyelid position without addressing globe proptosis (Arch Ophthalmol. 2004;122:1882-1885). This article will attempt to document the various surgical approaches for orbital decompression that have evolved over the years to treat TRO at the same time that the indications for what was once considered by many to be a fairly invasive orbital surgery have shifted.

Historical Overview

Historically, the primary indication for performing bony decompression in patients with thyroid orbitopathy (TRO) was vision threatening disease including but not limited to: (1) compressive optic neuropathy (CON), (2) globe subluxation, and (3) lagophthalmos.However, the techniques for surgical decompression have changed significantly since the first description by Dollinger in 1911. Indeed, Dollinger’s first published report of surgical decompression in 1911 advocated removal of the lateral orbital wall for decompression into the temporal fossa. Naffziger later reported removal of the orbital roof via a transcranial approach for decompression into the anterior cranial fossa. Meanwhile, decompression into the paranasal sinuses was first advocated by Sewell who described decompression into the ethmoid air cells, and Hirsch later reported inferior decompression into the maxillary sinus by removal of the orbital floor. Walsh and Ogura later combined the inferior and medial approaches into a single, transantral decompression.

The Transantral Approach

The transantral approach is a classic technique used in decompression surgery. This technique allows access to the maxillary sinus and the inferomedial walls of the orbit. The sublabial incision avoids visible cutaneous scars. This route also allows excellent visualization of the floor and inferior portion of the medial wall. Although dissection may be carried to the level of the posterior wall of the maxillary sinus, visualization of the orbital apex, posterior ethmoids, and lateral wall of the sphenoid sinus is difficult. In addition, oroantral fistulas, infraorbital hypesthesia, sinusitis, and cerebrospinal fluid (CSF) leaks may be more common with this technique. The transantral approach to decompression is also associated with a high incidence of postoperative strabismus. In many patients who have no preoperative diplopia, other types of decompression procedures should be considered.

The Transconjunctival Approach

The transconjunctival approach has become a popular approach for surgery of the orbital floor. This technique provides excellent visualization of the orbital floor and medial wall. However, visualization of the most posterior portion of the medial wall, which must be adequately removed for treatment of CON, may be suboptimal in this approach. The advantage of the transconjunctival approach is the lack of a skin incision, thus limiting the risk of lower eyelid retraction that is often problematic in patients with TRO even prior to surgery.

The Transnasal Approach

More recently, endonasal orbital decompression with the use of endoscopy has been shown to be effective in the treatment of CON (Am J Rhinol. 2005;19:603-606). Endoscopic transnasal decompression allows the removal of the orbital floor and medial wall, especially at the orbital apex. Visualization of the medial orbital wall is superior to other approaches, permitting more complete medial, posterior orbital wall decompression. However, the transnasal approach is limited by the fact that extensive endoscopic experience is required to safely perform endoscopic decompression.

Furthermore, access to the anterior orbital floor is limited. Anatomic variations such as a deviated septum may make this approach difficult. Endoscopic instrumentation may also be incapable of removing thickened bone in select cases. Finally, endonasal decompression requires a complete ethmoidectomy to enable visualization of the medial orbit. Thus, the transnasal approach does not allow for graded removal of the ethmoid air cells. When dissection is carried out from the medial wall of the orbit towards midline in the periorbital approach, the degree of orbital soft tissue proplapse is more easily controlled.

The Transcaruncular Approach

The transcaruncular approach, which has also been used for treatment of medial wall fractures and removal of apical tumors, is an excellent method of access for removal of the medial wall and medial portion of the floor of the orbit. However, the surgeon must possess intimate knowledge of the anatomy of the caruncle to safely use this approach without damaging delicate ocular, lacrimal, and medial canthus structures. The anatomy underlying the transcaruncular approach offers the same exposure of the medial wall and apex as the now defunct Lynch incision, which consisted of a 3-4 cm, cutaneous incision centered midway between the medial canthus and the nasal dorsum, without skin incisions or disruption of the medial canthal tendon. Any dissection proceeding posteriorly along the medial wall via a skin incision has been shown to cause a measurable amount of telecanthus. In addition to excellent visualization, the transcaruncular approach allows for the graded removal of ethmoid air cells, direct access to the lateral wall of the sphenoid sinus, and the ability to preserve the periosteum in selected cases for control of postoperative diplopia (Plast Reconstr Surg. 2003;112:739-747).

Other Approaches

Other approaches offer access to the orbit with their own particular advantages and disadvantages. The coronal flap requires a large scalp incision and may result in prolonged recovery time without offering any significant advantage in visualization of the orbital apex over a more direct approach. The transfrontal decompression has significant risk of CSF leakage, meningitis, and transmission of cerebral pulsations to the eyes.

Lateral Wall Decompression

Recent manuscripts have focused on removal of the lateral wall of the orbit and the greater wing of the sphenoid as an effective technique for reducing proptosis while minimizing the risk of postoperative diplopia. Several studies have demonstrated that removal of the lateral wall of the orbit can potentially provide significant amounts of expansile space for the orbital contents with minimal incidence of postoperative diplopia (Am J Ophthalmol. 2005;140:642-647). In the author’s experience (unpublished data) removal of the lateral wall of the orbit including the body of the greater wing of the sphenoid to the level of the temporal lobe dura and the superior orbital fissure without adjunctive procedures reduced exophthalmos by approximately 4.5 to 5 mm with less than 5% postoperative diplopia.

Advocates of lateral wall decompression for treatment of TRO without CON will note that exodeviation caused by expansion of the lateral wall is easier for the human visual system to fuse than the esodeviation or vertical deviations typically caused by decompression into the paranasal sinuses. Although this procedure has not been demonstrated to be effective for treatment of CON, the significant reduction in exophthalmos in combination with a low risk of diplopia suggest that aggressive removal of the lateral wall is an excellent choice for patients without preoperative diplopia or as an adjunctive procedure in patients with large amounts of proptosis.

Treatment Guidance Systems

In selected cases, image guided surgery that shows the precise location of selected surgical instruments in relation to surrounding structures may be helpful. The advantage of this type of equipment is to avoid entering vital areas such as the brain when working in areas where visualization may be less than optimal. Initially developed for localization of lesions during neurosurgical procedures, treatment guidance systems such as the Medtronic Xomed LandmarX allow tracking of the surgery in real time. Although expensive and cumbersome, the use of this instrumentation may assist transition surgeons who are inexperienced in operating in this region.

Summary of Recommendations

Decompression of the medial wall of the orbit continues to be the treatment of choice for relieving crowding of the orbital apex, but it fails to alter the underlying pathophysiologic process causing TRO. Once surgery has been performed, the surgeon must maintain vigilant watch for other potential causes of visual loss. Only after potentially blinding complications have been treated, and eye findings have been stabilized for a minimum of 3 months can attention then be turned to the treatment of strabismus, eyelid retraction, and other functional and cosmetic concerns. For most other patients with unsightly manifestations of TRO, removal of the lateral wall of the orbit provides the best primary option for treating disfiguring TRO. Nevertheless, physicians should familiarize themselves with all the potentially sight threatening complications of TRO and the methods for evaluating and treating these complications.

References

Author Disclosure

The author states that he has no financial relationship with the manufacturer or provider of any product or service discussed in this article or with the manufacturer or provider of any competing product or service.