33.1 Goals

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  Functional and aesthetic rehabilitation for thyroid-associated orbitopathy (TAO) or Graves ophthalmopathy. ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9 ,​ 10} By surgical expansion of lateral orbital wall, the orbital cavity is expanded and hence, this will reduce orbital pressure, proptosis, and pressure on the optic nerve. ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9}

  
  
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  This chapter focuses on lateral orbital wall decompression which is the most common type of bone removal orbital decompression (BROD). Depending on the severity of the TAO, lateral wall orbital decompression may be used alone or in combination with multiple walls orbital decompression, and orbital fat can also be removed during the procedure for additional effect.

33.2 Advantages

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  There are two main types of orbital decompression, BROD, and fat removal orbital decompression (FROD). Compared with FROD, BROD has broader indications and more effective results of proptosis reduction. In the BROD, theoretically, all four orbital walls could be removed for the decompression; however, lateral, medial, and floor decompression are routine choices for the clinical therapy. The orbital roof is usually spared. ^{1 ,​ 11 ,​ 12 ,​ 13 ,​ 14 ,​ 15 ,​ 16 ,​ 17 ,​ 18 ,​ 19 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 26 ,​ 27 ,​ 28}

  
  
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  Depending on the severity of the proptosis, lateral wall decompression could be customized by removing different areas and portion of the lateral wall. ^{11 ,​ 12 ,​ 13 ,​ 14 ,​ 15 ,​ 16 ,​ 17 ,​ 18 ,​ 19 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 26 ,​ 27 ,​ 28}

  
  
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  The incidence of new-onset diplopia after pure lateral wall decompression is about 0 to 6%. The effect of ocular motility, as evaluated by the Hess screen, is minimal. ^{21 ,​ 26 ,​ 29 ,​ 30 ,​ 31 ,​ 32}

  
  
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  Balanced decompression refers to lateral wall decompression combined with medial wall decompression (i.e., lamina papyracea removal and ethmoidectomy). The orbital decompression effect is more than isolated lateral wall decompression. Compared with inferomedial orbital decompression or floor decompression, there are fewer complications such as hypoglobus, muscle imbalance, and hypesthesia. ^{33 ,​ 34 ,​ 35 ,​ 36}

  
  
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  Indications for lateral wall decompression include both type I TAO (fat predominant disease without muscle enlargement) and type II TAO (muscle predominant disease). ^{11 ,​ 12 ,​ 13 ,​ 14 ,​ 15 ,​ 16 ,​ 17 ,​ 18 ,​ 19 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 26 ,​ 27 ,​ 28}

  
  
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  Compared to FROD, lateral wall decompression can achieve more proptosis reduction. Lateral wall decompression can also relieve compression in dysthyroid optic neuropathy (DON), improve exposure keratopathy, and reduce severe orbital congestion. ^{23 ,​ 29 ,​ 30 ,​ 37 ,​ 38 ,​ 39 ,​ 40 ,​ 41 ,​ 42 ,​ 43 ,​ 44 ,​ 45 ,​ 46}

  
  
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  Favorable cosmetic outcomes can be achieved with an eyelid crease, swinging eyelid, or lateral canthal approach without a detectable cutaneous scar. ^{29 ,​ 30 ,​ 37 ,​ 45}

  
  
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  Lateral wall decompression may be combined with FROD to augment the degree of proptosis reduction.

33.3 Expectations

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  Lateral wall decompression can improve the cosmetic appearance due to disfiguring proptosis for TAO patients who are in their inactive phase of the disease.

  
  
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  For those TAO patients with active orbital inflammation and sight-threatening complications such as compressive optic neuropathy, corneal decompensation, or acute globe luxation, BROD such as lateral wall decompression can be helpful.

  
  
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  Lateral wall decompression could achieve the proptosis reduction of 2.7 to 4 mm. When combined with fat removal, the proptosis reduction could reach 4.5 mm, especially for the patients with severe proptosis. ^{23 ,​ 26 ,​ 29 ,​ 30 ,​ 37 ,​ 44 ,​ 45 ,​ 46}

  
  
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  The percentage of new-onset diplopia is about 0 to 6%. ^{21 ,​ 22 ,​ 26 ,​ 29 ,​ 30 ,​ 31 ,​ 32}

  
  
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  In active TAO without sight-threatening complications, the treatment aim is to control the orbital inflammation first, usually by means of steroid, immunosuppressive agents, or orbital irradiation. Orbital decompression should be deferred until inflammation settles.

  
  
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  Patients may still need strabismus and eyelid surgeries for the complete ophthalmic rehabilitation after the lateral wall decompression. ^{47 ,​ 48 ,​ 49 ,​ 50 ,​ 51 ,​ 52}

33.4 Key Principle

Preoperative high-resolution CT scans in both axial and coronal planes are mandatory for evaluating the amount of bone present in the great wing of the sphenoid, the amount of intraconal fat, the size of the extraocular muscles (EOM), and the size of sphenoid trigone.

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  In our experience, the “skiving” of lateral wall is suitable for those cases with the proptosis less than 23 mm. For more severe cases with proptosis more than 23 mm, creating a lateral wall bony window is a more preferred approach, and sometimes with the combination of FROD. In patients with small trigone, lateral bone decompression alone will have limited effect on proptosis.

  
  
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  When using the high-speed diamond tip burr for skiving the lateral wall, it is important to establish a safe depth, then extend to the inferior and superior part of sphenoid when the inner table of the great wing of the sphenoid bone has been reached, the color has changed to a more pale appearance and the burr should not go deeper preventing tearing the dura causing the cerebrospinal fluid (CSF) leakage.