Chapter 144 Enucleation for Choroidal Melanomas
Approximately 5% of all melanomas occur in the eye and surrounding adnexal structures and 85% of these are uveal in origin.1 Uveal melanomas are the most common primary intraocular malignant tumor.2 According to one report, the overall incidence of uveal melanomas is 5.1 per million and 80–90% of uveal melanomas involve the choroid.3
Over 30 years ago, Zimmerman investigated the benefit of enucleation in eyes with choroidal melanoma.4 He observed a peak in mortality 2–3 years after enucleation and suggested that the rise of post-enucleation mortality was a direct result of the enucleation.4 This controversy led to the trend away from enucleation towards vision and eye-sparing treatments. Subsequent studies have demonstrated that the observed post-enucleation rise in mortality was a reflection of natural history of the primary tumor and its metastases rather than direct effects of enucleation causing iatrogenic tumor seeding. Metastasis was independent of the method of treatment.5
For the treatment of the primary tumor, there are many therapeutic options such as observation, transpupillary thermotherapy, plaque radiotherapy, local resection, and enucleation.2 In the USA, the two most frequently used methods of treatment are plaque radiotherapy and enucleation.2 The COMS demonstrated no statistical difference in all-cause mortality between the brachytherapy and enucleation arms in either medium or large choroidal melanomas.6
As mortality data show, no significant difference between enucleation and brachytherapy, quality-of-life (QOL) measurements become important in deciding on a therapeutic plan. The Collaborative Ocular Melanoma Study (COMS) ascertained QOL measures of driving difficulties, near vision activities, activities requiring stereopsis, anxiety levels, and depression levels.7 Patients reported higher levels of function for driving and peripheral vision in the brachytherapy arm compared to the enucleation arm for the first 2 years post-treatment but these differences diminished 3–5 years post-treatment.7 Patients in the brachytherapy arm also had more symptoms of anxiety after treatment compared with the enucleation group.7 Enucleation still remains a viable treatment option for choroidal melanoma in the proper setting.
The COMS group demonstrated a cumulative metastasis rate of 25% at 5 years and 34% at 10 years.8 Once metastasis occurs, the median survival time is 3.6 months, and death is inevitable as there are no effective treatment options at present.8,9
The main indications for primary enucleation are large tumor size, neovascular glaucoma, optic nerve invasion, blind painful eye, localized extrascleral extension, and patient preference. Enucleation is also considered for the treatment of medium-sized choroidal melanoma with poor vision (<20/400) or absence of potential for visual recovery. Functional status of the other eye and patient preference are also important considerations in the decision-making process. The indications for secondary enucleation are local treatment failure and ocular pain secondary to radiation-related complications.
An ideal implant should restore volume, transmit motility, possess a low complication rate, and demonstrate cost-effectiveness.10 To transmit motility, the extraocular muscles should attach to the implant directly or surround the implant indirectly.10 An implant of proper size restores volume.11 Current orbital implant designs fall into two general categories: solid spheres and porous, integrated implants. Solid spheres include silicone and polymethyl methacrylate (PMMA), while porous implants include coralline hydroxyapatite and porous polyethylene.10 Bioceramic and other implants also exist.10 Porous materials allow for fibrovascular ingrowth which may induce epithelialization of a drill hole to accept a prosthesis coupling peg to improve motility. Pegged hydroxyapatite implants offer subjective improved motility over unpegged implants and vascular ingrowth possesses some theoretical advantages, including decreased rates of infection, exposure, and extrusion.10,12
Coralline hydroxyapatite (HA) is a porous, nontoxic implant composed of inorganic, nonreplenishable marine coral.13 High-density porous polyethylene is a porous, synthetic implant that can be molded into various shapes.14 Hydroxyapatite has a brittle nature, which precludes direct suturing to the implant surface.15 Pore sizes and interconnectivity vary, which could affect vascularization.16 Some surgeons drill holes into porous implants to facilitate integration.17 The use of porous materials adds additional costs of the implant, wrapping material, and imaging studies, and possesses higher complication rates.18
Some surgeons wrap porous implants to protect the anterior tissues from hydroxyapatite bone spicules and to facilitate muscle attachment and implantation. However the perceived benefits have not been proven.15 Wrapping materials include donor sclera, autogenous fascia or polyglycolic acid mesh. While some surgeons wrap porous polyethylene implants, the extraocular muscles can be directly sutured to polyethylene.19,20 Wrapping materials may pose infection risk and decrease vascularization rates.17
When surveyed in 1995, the majority (56%) of the American Society of Ophthalmic Plastic and Reconstructive Surgeons (ASOPRS) preferred hydroxyapatite implants and human donor sclera wrapping in enucleations.21 When resurveyed in 2002, the majority (43%) of ASOPRS surgeons preferred porous polyethylene and only 27% preferred hydroxyapatite.18 In the later survey, most implants (60%) were not wrapped and only 25% were wrapped in human donor sclera.18 The majority (92%) of implants were left unpegged.18 In 2007, a survey from the UK supported these trends, demonstrating that 55% of surgeons used porous implants, 57% wrapped the implant (with autogenous sclera being most popular; 20%), and only 7% pegged the implants.22 Custer demonstrated no significant difference in motility between unpegged hydroxyapatite and solid implants.23 The potential advantages of using porous implants and wrapping materials should be weighed against the risks, morbidity, and additional cost.20 If the surgeon does not plan to peg, if the patient has systemic illnesses or factors that may limit fibrovascular ingrowth, or if a porous implant may not improve a patient’s quality of life, the surgeon should give consideration to a solid implant.
Proper implant sizing is essential for cosmesis, volume restoration, and to minimize extrusion, exposure, and sulcus deformities. Most adult patients require at least a 20 mm implant. Traditionally, surgeons use a set of sizing spheres to individualize implant size and use standard volume tables to maximize volume restoration. Alternatively, orbital implant size can be determined using the contralateral eye axial length measurements subtracted by 2 mm, or by 3 mm for hyperopia.11 Another algorithm subtracts the volume of an ideal 24 mm eye by the volume of sclera and 2 mL to determine implant volume.24