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The optimal management of small posterior choroidal melanomas remains controversial, especially for tumours located near the optic disc and fovea. Although with increasing rarity, argon laser photocoagulation continues to be used in the primary treatment of small tumours, despite data suggesting that other therapeutic methods may be more successful.1–4 More recently, transpupillary thermotherapy (TTT) has emerged as a therapeutic option for the primary treatment of small choroidal melanomas.5, 6 Initial results are promising, but like any new treatments, more widespread use and longer follow up are needed for a thorough assessment of its efficacy. As a cautionary reminder that additional study is required to define the potential complications of these treatments, we present a case of choroidal melanoma in which treatment with primary argon photocoagulation followed by TTT was associated with extrascleral extension of the tumour.
A 38 year old woman presented with decreased visual acuity in her right eye. An ophthalmologist noted a pigmented choroidal lesion with associated subretinal fluid. The lesion was initially treated with argon laser photocoagulation, but within a month the decision was made to re-treat the lesion with TTT. Over the next 7 months, visual acuity deteriorated to 20/200. The lesion exhibited persistent elevation and subretinal fluid. By ultrasound, a change in the retroscleral echogenicity was observed, precipitating referral to an ophthalmic oncologist whereupon a diagnosis of choroidal melanoma with extrascleral extension was made. The patient was then referred to UCSF for consideration of proton beam therapy.
On examination, all abnormal findings were confined to the right eye. The patient's visual acuity was counting fingers at 2 feet. Funduscopic examination revealed a raised pigmented tumour centred on the fovea, measuring 7 mm vertically by 10 mm horizontally, extending to within 2.3 mm of the disc. Subretinal fluid was present and extended over the nasal aspect of the tumour (Fig 1A). A flat naevus 2 mm in diameter was also noted inferonasally (not shown). Fluorescein angiography was remarkable for an irregular plexus of choroidal vessels within the tumour noted in the early arterial phase, mid-phase leakage from retinal veins overlying the tumour, and late leakage with punctate hot spots at the tumour margin (Fig 1B). B-scan ultrasound revealed choroidal excavation, an acoustic quiet zone, and orbital shadowing (Fig 2A). A-scan demonstrated spontaneous pulsation, low to medium internal reflectivity, and a sharp posterior spike (Fig 2B). The intraocular thickness was 3.0 mm, with 7.7 mm of extraocular extension. These findings are consistent with choroidal melanoma with posterior extrascleral extension. Systemic evaluation revealed no signs of metastasis. The potential for orbital contamination by tumour made focal therapy by proton beam a less desirable alternative. Therefore, enucleation with en bloc resection of the extrascleral tumour was recommended and subsequently performed. Pathological examination confirmed the diagnosis of malignant choroidal melanoma, mixed cell type, with extensive extrascleral extension and focal vascular invasion. The patient elected to undergo adjuvant post-surgical external beam irradiation to reduce the rate of orbital recurrence, with the understanding that this treatment, while not definitively harmful, is of unproved benefit.7 She was also referred to the medical oncology service for systemic therapy and has begun an experimental treatment protocol using interferon alfa. Systemic chemotherapy is currently under consideration.
Options for the management of choroidal melanoma include observation, laser photocoagulation, transpupillary thermotherapy, charged particle radiotherapy, brachytherapy, local resection, and enucleation. Argon laser photocoagulation is typically used as an adjunct to other treatments,2 but in select cases has been used as primary therapy for choroidal melanoma.1–3 Typically, photocoagulation is reserved for small tumours (less than 3–4 mm in thickness and less than 10 mm in diameter) that are located close to the fovea and/or the optic disc in eyes with good vision. Because the level of tumour necrosis with laser photocoagulation is shallow (0.2–0.8 mm),8 multiple sessions are often necessary.2, 3 Therefore, the greatest challenge to successful photocoagulative therapy in choroidal melanomas is determining when the tumour has been fully ablated.9
TTT shares the advantages that photocoagulation has over radiotherapy, including the more rapid visible reduction of tumour size, the relative sparing of adjacent normal tissue, and the convenience and economy of an outpatient procedure. In contrast with the shallow penetration of the argon laser, however, TTT employs near infrared light to produce up to a 3.9 mm depth of tumour necrosis.10 The promise of this treatment has spurred investigation into its use as a primary treatment for small posterior choroidal melanomas with encouraging early results.5, 6
It has been suggested that recurrences occur following apparently successful photocoagulation or TTT because invisible nests of malignant cells can infiltrate the sclera, a histologically documented phenomenon.11, 12 The presented case serves as a reminder that this possibility is not trivial. Extrascleral extension, presumably from tumour out of reach of initial argon phototherapy and subsequent TTT, resulted in a requirement for aggressive local surgical therapy, radiation therapy, and adjuvant systemic therapy to reduce the risk of metastatic disease. The unusual degree of extrascleral extension for a small melanoma also raises the possibility that either photocoagulation or, more likely, TTT produced some reduction in scleral integrity allowing focal egress of tumour cells. Reports of complications following argon laser are likely to become rarer because advances in modern radiotherapy have made primary photocoagulation an uncommon treatment.4 The use and investigation of TTT, however, continue to increase and the risks for extrascleral extension remain undefined.