35.1 Goals

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  Aesthetic and/or functional rehabilitation for thyroid eye disease (TED) or Graves’ ophthalmopathy are the main surgical goal. By removing orbital fat alone, the orbital volume is reduced, resulting in proptosis reduction. ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8}

  
  
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  In this chapter, the term fat removal orbital decompression (FROD) refers to orbital decompression by orbital fat removal only. However, during bone removal orbital decompression (BROD), orbital fat can also be removed to augment the orbital decompression effect.

35.2 Advantages

There are two main types of orbital decompression: BROD and FROD. ^{9 ,​ 10 ,​ 11} Due to modification of surgical techniques, the improved safety profiles of both procedures have successfully decreased postoperative complications in surgical decompression of the orbit.

However, postoperative diplopia is still an important potential complication. Between the two methods, FROD has a lower quoted incidence of new-onset postoperative diplopia, with studies quoting figures as low as 2.8%. ⁴ The exact reason of low incidence of postoperative diplopia is not entirely understood. Since the bony orbital walls are not removed in FROD, it is proposed that there is less alteration in the position of extraocular muscles. Yet selection bias may also contribute, as FROD is indicated in type I TED (fat predominant disease) where there is no muscle enlargement. These patients are intrinsically less prone to develop diplopia. In contrast, those with type II thyroid associated orbitopathy (TAO; muscle predominant disease) more commonly have baseline diplopia. In FROD, the degree of proptosis reduction may be more predictable by controlling the amount of fat removed.

In FROD, since the procedure is isolated to the orbit with orbital bones preserved, the possibility of serious life or vision-threatening complications such as cerebrospinal fluid (CSF) leakage, dura exposure, and secondary meningitis is reduced. ^{4 ,​ 5 ,​ 6 ,​ 7 ,​ 8} Other potential complications related to BROD such as sinusitis, infraorbital nerve and minor sensory nerve paresthesia or injury, and optic nerve trauma are minimized or even avoided. ^{9 ,​ 10 ,​ 11}

Besides being a high-benefit and low-risk procedure, FROD is also easy to perform in the hands of an experienced orbital surgeon.

35.3 Expectations

FROD can improve the cosmetic appearance due to disfiguring proptosis in type I TED patients (Fig. 35‑1) during the inactive phase of their disease.

In properly selected cases, the proptosis reduction usually ranges from 2 to 5 mm. ^{4 ,​ 5 ,​ 6 ,​ 7 ,​ 8} Therefore, FROD can be considered in patients with mild to moderate proptosis. However, in patients with severe proptosis, FROD alone may be inadequate.

The percentage of new-onset diplopia in pure FROD is about 2 to 3%. ⁴

FROD is not the procedure of choice in active TAO patients when the disease is not yet stable. Operating while there is active orbital inflammation will increase bleeding, operative difficulty, and hence the risk of complications and morbidity. In active TAO, the treatment aim is to control the orbital inflammation first, usually by means of corticosteroids, immunosuppressive agents, or orbital irradiation.

Generally, FROD is not very helpful in TAO with compressive optic neuropathy. In such cases, BROD (commonly of the medial ± lateral wall) is usually required. In selected cases, FROD may be helpful in patients with TAO with optic neuropathy due to stretching of optic nerve. ^{9 ,​ 10 ,​ 11}

Patients may still need strabismus and eyelid surgeries as part of the complete ophthalmic rehabilitation process.

35.4 Key Principles

In active TAO, inflammatory cells infiltrate the orbit with fibroblast activation and deposition of collagen and glycosaminoglycans (GAG) in the orbital and periorbital tissues. This is followed by scarring, fibrosis, and fat proliferation of the extraocular and levator muscles causing orbital volume enlargement. These changes in turn cause disfiguring proptosis from the limited confines of the bony orbital space. Some patients may develop more severe sight-threatening problems; for example, compressive optic neuropathy, exposure keratopathy, or diplopia.

Orbital decompression can be achieved either by expansion of the bony cavity (BROD) or removal of the orbital fat (FROD), or both.

In type I TAO, there is expansion of the orbital fat with minimal enlargement of extraocular muscles. By removing part of the orbital fat, there will be reduction in the retrobulbar orbital volume and hence proptosis.

In type II TAO, there is enlargement in extraocular muscles with less increase in orbital fat; hence, FROD is undesirable and BROD is the preferred option of orbital decompression in these cases.