Post Enucleation Socket Syndrome Study

Purpose:

Primary aim:

Three dimensional volumetric assessment of the changes in orbital soft tissues in patient with post-enucleation socket syndrome, using the new 16-slice multi-detector computed tomography scanner.

Background:

Post-enucleation socket syndrome (PESS - enophthalmos, superior sulcus deformity, ptosis or upper eyelid retraction and lower eyelid laxity1) is a well recognized late complication of enucleation surgery. The underlying pathophysiology, however, has not been well established. It is especially prominent when there is inadequate orbital volume replacement or contraction of the socket.2

Superior sulcus deformity (Fig.1) manifests as a deep groove or space between the upper eyelid and the superior orbital rim. In a review by Smerdon and Sutton, it was the only significant factor related to poor cosmetic satisfaction.3 It was suggested that the loss of orbital volume and relaxation of tissues were the causes.4

With the advance in orbital implant development, most patients received implant replacement during their enucleation surgery or shortly afterward to improve the cosmetic outcome. A survey among members of the American Society of Ophthalmic Plastic and Reconstructive Surgery reported a total of 2,779 primary orbital implant being performed in a year.5

An ideal orbital implant replaces 70-80% of the volume enucleated (\~5ml, i.e. implant size 20-22mm), while the ocular prosthesis fills the rest (\~2ml). But the predictions of implant size have been relatively subjective and inaccurate. They are influenced by factors like phthisis, configuration of the orbit, placement of the extraocular muscles, shape of the implant, the use of implant warps and the orbital fat volume.6 In a retrospective study by Kaltreider et al, 76% of the patients would benefit from a larger implant and 63% would need an implant size larger than 22mm.7 On the contrary, in a prospective study by Custer and Trinkaus, no implant of larger than 22mm was needed.8 However in both studies, patients with less volumetric replacement showed significantly more severe enophthalmos and superior sulcus deformity.

Different surgical procedures, mostly by secondary volume augmentation 9-19, have been suggested to treat superior sulcus deformity and PESS. They can be categorized into subperiosteal implants on the orbital floor or eyelid implants.20 Besides filling up the orbital volume, subperiosteal implants produce upward and forward displacement of orbital content to correct the superior sulcus deformity. Cosmetic improvement with the eyelid implants or filler material is achieved by adding bulk to the hollowed area below the brow and above the upper eyelid crease directly. In spite of these, information on accurate pre-operative volumetric assessment of the anophthalmic sockets remained inadequate, resulting in occasional revision of the volume augmented.21

Conventional imaging studies have been used for various oculoplastic conditions for more than two decades. In studying orbital anatomy and pathology, Nugent RA et al has demonstrated changes in the extraocular muscle (diameter \& volume) in patients with Graves' orbitopathy with the second generation CT scanner and found to correlate well with the clinical findings22. In the area of anophthalmic sockets, both computed tomography (CT) and magnetic resonance imaging (MRI) have contributed to the understanding of the condition. With the use of high resolution CT, Smith et al had demonstrated deepening of the superior sulcus, sagging \& retraction of the superior muscle complex, distal elevation \& retraction of the inferior rectus and downward \& forward redistribution of the orbital fat in 22 anophthalmic sockets without orbital implant insertion. They had further suggested a rotatory displacement of orbital content from superior to posterior and from posterior to inferior.23 In anophthalmic sockets with orbital implant, Detorakis's group had used 2mm cut MRI scan to demonstrate statistically insignificant decrease in rectus muscles volume and no change in orbital fat volume in 5 patients with enucleation surgery.24 Despite the information obtained, there were multiple drawbacks: poor image quality for detailed volumetric assessment, increased radiation exposure with separate scanning in axial and coronal planes, contra-indicated in patient with metallic foreign body injury, and long exposure time with possible motion artifact,25 and neither of the investigations have been translated into pre-operative volumetric assessment for surgical planning.

Multi-detector CT (MDCT) is the newest advance in CT technology. It provides unparalleled capabilities for detailed analysis of normal anatomy and pathology. MDCT allows very high resolution sub-millimeter image acquisition, and potentially true isotropic datasets, which is important in the production of good quality images on multi-planar reformation and volumetric assessment. In the study of anophthalmic sockets and PESS, high quality three dimensional reconstruction images mean accurate analysis of orbital soft tissue without the need of additional CT acquisition in a different plane. In a study comparing radiation exposure between MDCT and conventional CT in the imaging of para-nasal sinus, Zammit-Maempel et al have demonstrated an 84% reduction in radiation exposure with MDCT, the radiation dose of 9mGy was 54 times less than the threshold dose of 0.5-2Gy for detectable lens opacities26. Moreover, since the required coverage is less in the imaging of anophthalmic sockets, we can expect an even smaller and safer dose of radiation exposure. Last but not least, the 16-slice MDCT scanner is faster than conventional scanner, it can shorten the examination time and minimize motion artifact.

Despite all the published data, the patho-physiology of PESS remained unclear and the management of it is far from satisfactory. We are planning to answer some of the questions with anophthalmic sockets in 3 stages:

1. Anatomical and radiological analysis

   1. With this pilot study we are trying to identify the volumetric changes and the changes in anatomical relationship of the orbital soft tissue in anophthalmic sockets by comparing with contra-lateral eyes.
   2. Although MRI provide superior soft tissue contrast, CT still provides better detail of the eye, orbital soft tissue and bony orbit which is important for pre-operative surgical planning of secondary sub-periosteal orbital implant27.

2. Bioengineering and animal study (with the information obtained in part 1)

   1. We will assess the usefulness of MDCT in i. correct sizing of primary orbital implant in preventing PESS; and ii. correct sizing and effective placement of secondary orbital implant in restoring both the volumetric and positional changes in PESS.
   2. In addition, with the use of VGStudio MAX software, we may be able to offer customized secondary orbital implant for optimal correction of PESS.
3. Clinical trials