The morphology of human papillomas of the upper respiratory tract.

Recurrent squamous papillomas of the upper respiratory tract were examined by light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Surface of the cells is irregular and is covered by numerous stout microvilli. These are shorter and broader than those of cells of the uninvolved mucosa. The villi often seem umbilicated at the apex; the remainder of them, however, are rounded. The epithelium participating in the formation of papillomas shows some maturation of the cells but this does not progress normally. The predominating area is the thickened spinous layer representing the bulk of the lesion. The basal layer shows mildly increased activity but the basement membrane is intact. The cells often are very closely packed but in some areas, more particularly in the deep layer, they are loosely arranged. The intercellular space contains a moderately electron-dense finely fibrillar material. No abnormal mitoses are found. The neighboring univolved epithelium often shows increased growth activity and some inflammation. The larygneal papillomas propably represent an overgrowth of epithelium which may develop following hindered desquamation caused and/or heralded by a chronic inflammatory condition probably of viral origin and may be preceded by epithelial metaplasia and hyperplasia.