Benign conjunctival melanocytic lesions. Clinicopathologic features

The common acquired conjunctival nevus usually undergoes progressive maturation and only exceptionally gives rise to conjunctival melanoma. Pure junctional nevi are rare except in childhood. Histologically, however, a junctional nevus may be indistinguishable from primary acquired melanosis (PAM) with atypia, a condition of middle-aged and elderly individuals that has a tendency to evolve into melanoma. Nevi in adolescents may attract a vigorous lymphocytic response and may cause clinical and histologic confusion with other entities, particularly a regressing nodule of melanoma that occurs predominantly in adults. Rarely, congenital conjunctival nevi are identified, sometimes in patients with adjacent congenital nevi of the eyelid. A variety of unusual nevi, including balloon-cell nevi, Spitz nevi, epithelioid cell nevi, dysplastic nevi, recurrent nevi, episcleral melanosis and the nevus of Ota, blue and cellular blue nevi, melanocytoma, and composite or mixed nevi all may be identified in the conjunctiva. Concepts of histogenesis as well as the clinical, light microscopic, and ultrastructural features of these and other benign pigmentary conditions of the conjunctiva are described.