Phakomatous choristoma of the lower eyelid with psammoma body formation: a light and electron microscopic study.

A firm, round tissue mass, measuring approximately 12 mm in diameter, was excised from a 5-month-old boy who had a history of a gradually enlarging swelling in the left lower nasal eyelid since birth. Histologically and ultrastructurally, the lesion appeared benign and was composed of a dense connective tissue stroma in which nests, lobules, tubules, cords, and sheets of large, pale-staining cuboidal and elongated epithelial cells were surrounded by an irregular, thick PAS-positive basement membrane having focal excrescences. The interior of the epithelial islands contained "bladder" cells, cellular debris, granuloamorphous material, and foci of dystrophic calcification; an unusual feature of the lesion was the formation of numerous psammoma bodies. Tumors of lenticular anlage are rare and probably result due to displacement of migration of the inferior lens placode cells; alternatively, it may originate from an additional locus of lens vesicle in the primitive surface ectoderm of the lower lid. The lesion enlarges because of the differentiation of the ectopic lenticular cells in an abortive attempt to form a lens within the extraocular and mesodermal environment of the lid.