Ultrastructure of an intraocular lacrimal gland choristoma.

An intraocular lacrimal gland choristoma which was at first mistaken for a medulloepithelioma (diktyoma) was studied with the electron microscope. The tumour did not contain cells with neuronal and glial differentiation as expected in a medulloepithelioma but it did contain acini, ducts and dilated ducts or cysts. The tumour, in fact, bore much resemblance to the lacrimal gland, in that it contained electron-dense serous granules, and at times, a myoepithelial cell was detected at the base of an acinus. The ductal and cystic elements were lined by a single layer of cells or by stratified or pseudostratified epithelium. An interesting, unexpected feature was the occurrence of a myoid band (composed of thin filaments with focal densities along their course) under the cell membrane of the epithelial cells adjacent to the lumen of the ducts and cysts.