It is rarely seen in cervical scrape smears. In form of flat clusters of small, spherical or polygonal cells. Cells have scanty cytoplasm relatively large, dense but regular nuclei. The nuclei vary in size and shape and may show mitotic activity. The recognition of the basal endocervical cells is easier if well-differentiated columnar cells are attached to the periphery of such cluster.
It is a replacement of normal endocervical epithelium by squamous epithelium of varying degrees of maturity.It is very frequent even that may be confined to a small area of the endocervix and involves surface epithelium and the glands. Squamous metaplasia is a normal, physiological event during maturation of the female genital tract.
Atypical Squamous Metaplasia
Squamous metaplasia in tissue and smears show light to severe abnormalities. The slight changes are cell and nuclear enlargement or binucleation confined to a few cells within the cluster. Severe changes include: significance cellular and nuclear enlargement, variability in nuclear sizes, and coarse granulation of chromatin and presence of prominent nucleoli.
Tubal and tubo-endometroid Metaplasia
Endocervical epithelium show features of tubal or endometrial epithelium. Tubal metaplasia is a replacement of the normal epithelium lining the endocervical surface and gland by epithelium of tubal type such as columnar ciliated cells, clear secretory cells. Nuclear abnormalities may be significant and may classified as atypical glandular cells of unknown significance (AGUS)