LAUSR

Background Primary orbital melanoma is a rare disease and can occasionally develop from a pre-existing neoplasm of the blue naevus family of melanocytic lesions. Case presentation Herein we report a rare case of primary orbital melanoma arising from an unusual atypical diffuse (plaque-like) blue naevus/melanocytosis. A 27 year old man presented with mild pain and swelling of the left eye. Magnetic Resonance Imaging revealed a left lateral episcleral orbital mass and an incisional biopsy confirmed the diagnosis of malignant melanoma. Skin-sparing total left orbital exenteration was performed. Histopathological examination of the exenteration specimen revealed a primary orbital melanoma arising in a pre-existing blue naevus like melanocytosis. We demonstrate the evidence for histological progression, characterise the molecular profile of this tumour and discuss the related literature. Conclusions This case emphasises the importance of a meticulous clinicopathological correlation in recognising such a tumour as a primary orbital melanoma rather than a metastasis, which is managed differently.