Ultrastructural observations on bronchial epithelial hyperplasia and squamous metaplasia.

TLDR: It is concluded that diagnoses such as basal cell hyperplasia, stratification and flattening, and squamous metaplasia should be clearly differentiated and application of such criteria may result in more meaningful clinicopathologic correlations.

Abstract: Alterations in rat bronchial epithelium produced by 3-methylcholanthrene-coated steel pellets and those resulting from uncoated steel pellets were studied by light and electron microscopy. Exposure to uncoated pellets resulted in increased cell interdigitations, moderate stratification and flattening, and incomplete loss of cilia and polarity. In contrast, carcinogen-coated pellets produced complete loss of cilia and cell polarity and severe stratification. Increased cell interdigitations and desmosomal junctions as well as abundant cytoplasmic filaments, keratohyalin granules, and “membrane-coating granules” were also observed. Thus, only contact with a carcinogen produced cells capable of keratin synthesis. We conclude that diagnoses such as basal cell hyperplasia, stratification and flattening, on the one hand, and squamous metaplasia, on the other, should be clearly differentiated. The diagnosis of squamous metaplasia should be made only in the presence of clear evidence of keratin synthesizing cells. Application of such criteria may result in more meaningful clinicopathologic correlations.