[Metaplasia and high grade CIN. Diagnostic difficulties]

Squamous metaplasia of cervix represents the physiologic process of transformation of eversed glandular tissue at external orifice by a malpighian tissue. Primarily undifferentiated and immature, the epithelium progressively becomes differentiated and takes glycogen. In a high grade CIN the normal squamous epithelium is replaced by an undifferentiated tissue comporting basal cells with nuclear atypias. When cellular abnormalities are not marked, differential diagnosis exists with immature metaplasia. Cytology with suspicion of squamous intraepithelial lesion is sometimes followed by a diagnosis of high grade CIN on biopsy, but conisation reveals a metaplasia.