Occult anterior uveal melanomas presenting as extrascleral extension

Subconjunctival Ocular Argyrosis following Treatment with Ruthenium 106 Brachytherapy for Choroidal Melanoma

Introduction

Ruthenium-106 (Ru-106) brachytherapy is one of the commonest eye-sparing treatments for choroidal melanoma. These patients require long-term surveillance of the treated tumour remnant to ensure there is no local recurrence. New or progressive pigmented lesions in treated eyes are often regarded as suspicious - especially if there are concerns of extra-scleral extension.

Case Presentations

We present two cases of posterior choroidal melanoma treated five and 10 years previously with Ru-106. Both cases developed subconjunctival dark/black lesions on the anterior surface of the eye in the quadrant of the conjunctival peritomy during Ru-106 treatment. Both had similar findings on histopathology: black, non-organic, particulate foreign material of varying confluence deposited on elastin and collagen fibres. Energy dispersive X-ray microanalysis confirmed the material contained silver.

Discussion

The Ru-106 applicator consists of a radioactive core of Ru-106 encapsulated within pure silver as a radiation shield. During surgical insertion, stainless steel suture needles and forceps can occasionally scratch the applicator's silver eyelets and scatter microscopic particles of elemental silver into the operative field. These particles were likely deposited within the subconjunctival tissues of these patients during brachytherapy administration, leading to localised ocular argyrosis. Iatrogenic ocular argyrosis should be considered in the differential diagnosis of new pigmented lesions in patients treated with Ru-106 brachytherapy. This study is the first to unequivocally identify the cause of some post-brachytherapy ocular surface pigmentation as caused by silver.