31 Uveal Melanoma

Uveal Melanoma

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 15/04/2020

associated with the worst prognosis. Around 40-50% of all patients diagnosed with UMwill developmetastasis, despite treatment, and in 90% of cases the liver is the target organ for metastasis, with survival time after metastasis averaging 6–12 months. Most UM are initially asymptomatic. As the tumour enlarges, it may cause distortion of the pupil (iris melanoma), blurred vision (ciliary body melanoma), or markedly decreased visual acuity caused by secondary retinal detachment (choroidal melanoma). Serous detachment of the retina may occur. If extensive detachment occurs, secondary closed-angle glaucoma occasionally develops. Treatment of primary uveal melanoma is either globe-conserving therapy or enucleation. Among radiation therapies, plaque brachytherapy has the lowest rate of treatment failures. The two most widely used forms of radiation therapy, Iodine-125 and Ruthenium-106 brachytherapy are both associated with a weighted average local recurrence rate of 4-15%; however the recent introduction of the intraoperative ultrasound plaque localization during brachytherapy has been shown to reduce the risk of local treatment failure. Stereotactic radiotherapy has similar rates local failure of 2-7.9%, charged particle radiation therapy, however, has a lower weighted average rate of local failure at 4.2% and this treatment modality should be discussed in tumour boards as alternative treatment for large, completely encircling juxtapupillary melanomas. Overall, surgical modalities have a higher rate of local failure compared with radiation modalities (18.6% vs 6.15%). Transpupillary Thermotherapy has the largest reported variation of failure from 0% to 55.6%, with a weighted average of 20.8%. The globe is composed of three tunicae. The outer coat consists of the opaque fibrotic sclera (containing mainly collagen with only few fibroblasts) with a thickness of 0.3 to 1.0 mm and a diameter of 24 mm (which tolerates extremely high radiation doses), to which the six ocular muscles controlling the eye movement attach, and the clear cornea. The uvea (middle coat) is formed by the choroid (thickness 0.1 - 0.3 mm), the ciliary body (thickness 2 mm), and the iris (thickness 0.5 - 3 mm), which represents the origin of different types of uveal melanoma. The inner coat consists of the retina including the retinal pigmented epithelium (thickness 0.1 mm). The vascular supply for the retina is derived from the central retinal artery entering the globe through the optic nerve. The vitreous body filling the inner part of the globe does not contain any vital cells. The optic nerve enters the globe at the optic disc (papilla of the optic nerve). The three tunicae of the globe stop at the border of the optic disc. The macula represents the point of the sharpest sight and is therefore most important for the overall function of the eye and is located temporal to the optic disc (3 mm). (Fig. 1) 3. ANATOMICAL TOPOGRAPHY

Fig. 1: ocular anatomy and uveal melanoma

tumour was located in the iris in 285 (4%), ciliary body in 492 (6%), and choroid in 7256 (90%) cases. Choroidal melanoma usually presents as a brown, elevated, well defined, pigmented subretinal mass. The major growth pattern (75%) is towards the inner part of the globe resulting in a dome- shaped configuration . At the same time, the tumour frequently spreads along the choroid or along the inner part of the sclera (up to 50%). The overlying retina is most often damaged for various reasons (e.g. through impaired blood supply). In more than 25% nodular tumours erode through Bruch`s membrane, which covers the choroid. Because of its elasticity this membrane cuts into the tumour, leading to a typical mushroom configuration , in which the surface of the mushroom may sometimes be larger than its base. In this configuration particularly, different forms of retinal tumour invasion are seen as well as cellular spread into the vitreous body. Choroidal melanoma can lead to a serous retinal detachment in its direct vicinity and far away at the caudal part of the fundus following gravity. The optic nerve is almost never infiltrated, even in juxtapapillary tumours. Extraocular extension is present at the time of diagnosis in 3–5.8% of the patients with uveal melanoma. A Diffuse configuration with infiltrating flat choroidal tumours is rare. The degree of pigmentation ranges from dark brown to totally amelanotic. Clinically, several lesions can simulate choroidal melanoma, includingmetastatic carcinoma, posterior scleritis, and benign tumours, such as nevi and hemangiomas. Iris melanoma can be circumscribed (90%) or diffuse (10%). In most cases, it is an incidental finding due to iris color changes (heterochromia) and pupil distortion (corectopia). It is most commonly located in the inferior quadrant, and because of its clinical appearance it is detected at an early stage. Diffuse iris melanoma has an infiltrative, flat, ill- defined growth pattern with confluent or multifocal iris involvement. The diagnosis of diffuse iris melanoma is challenging and is often delayed. The classic findings of diffuse iris melanoma include acquired hyperchromic heterochromia iridis and ipsilateral glaucoma. Ring melanoma of the anterior chamber is a distinct rare variant that manifests as circumferential, flat tumour growth confined to the trabecular meshwork and anterior chamber angle structures. It presents as refractory unilateral glaucoma simulating pigmentary glaucoma and can be diagnosed only by gonioscopy and ultrasonography.

4. PATHOLOGY

The most common site for uveal melanoma is the choroid. In a study of 8033 patients with uveal melanoma by Shields et al , the