UNILATERAL EXOPHTHALMOS DUE TO ORBITAL METASTASIS FROM A CONTRALATERAL INTRAOCULAR MELANOMA

Progressive, left exophthalmos developed due to a left, retrobulbar ma ss in a 76-year-old Japanese woman. An open tumor biopsy was carried o ut, and both macro- and microscopic findings of the mass confirmed tha t it was a malignant melanoma. Orbital melanomas usually result from d istant metastasis of cutaneous melanomas or from secondary extension o f ipsilateral intraocular melanomas. Thorough physical, laboratory, an d radiological examination, however, did not disclose any primary cuta neous or visceral melanoma, nor had the patient any previous history o f excision or spontaneous regression of a pigmented lesion. Histopatho logically, the left retrobulbar melanoma was rich in sinusoidal vessel s which were surrounded by melanoma cells, oriented in a perpendicular array, a histological feature more characteristic of uveal melanomas than of cutaneous ones. The ophthalmological examination excluded deve lopment of a primary intraocular melanoma on the left side. Fundoscopi c examination of the right eye was not feasible because of the complet e opacity of the right vitreous body which had resulted from previous episode of idiopathic vitreous hemorrhage, Unexpectedly, CT and MR stu dies depicted retrobulbar masses of non-homogeneous densities in the b ilateral orbits. These radiologic studies indicated the metastatic nat ure of the left retrobulbar melanoma, while suggesting the development of a primary, intraocular melanoma on the right side, extension into the right orbit, and involvement of the right optic nerve. All these c linical, radiological, and histological data suggested the development of a primary melanoma in the right eye and subsequent metastasis to t he left orbit producing exophthalmos. The mechanism of such a peculiar mode of metastasis remains entirely unknown. This is a rare case of m etastatic orbital melanoma, without visceral involvement, which origin ated in the contralateral eye. Development of the right ocular melanom a remained unrecognized due to atrophic degeneration of the right eyeb all and complete opacity of the right vitreous body, until the contral ateral orbital metastasis grew massive enough to cause exophthalmos.