Ultrastructural pleomorphism in medulloepithelioma of the ciliary body: a comparative study of tumour cells and fetal ciliary epithelium.

A locally aggressive nonteratoid intraocular medulloepithelioma occurring in a two-year-old boy was studied by electron microscopy. For comparison the primitive pars plana region was examined in human fetal eyes obtained at 16, 18 and 22 weeks of gestation. The tumour was polymorphic with neural, intermediate and epithelial components. The neural component of the tumour resembled the zonulae adherentes dominant cell junction seen in the apical part of the unpigmented epithelium at 16 weeks, while the well-developed junctional complexes and interdigitations seen in the unpigmented epithelium at 22 weeks resembled those in the epithelial component of the tumour. Intermediate cells which exhibited characteristics of both neural and epithelial components, particularly in the cell junctional features, were found. Pleomorphism in nonteratoid medulloepithelioma might be accounted for by the developmental stage at which the tumour is initiated.