Dysplasia

In pathology, dysplasia means disordered growth in which the cells of a tissue, usually an epithelium, look abnormal under the microscope and lose their normal orderly arrangement. Dysplastic cells vary in size and shape, have large, darkly staining nuclei and divide more often than usual, and the normal maturation of cells from the base of the layer to its surface breaks down. The cells carry accumulated genetic changes but have not invaded through the basement membrane, the thin sheet beneath the epithelium, so dysplasia is not yet cancer.

Pathologists grade dysplasia as low grade (mild) or high grade (moderate to severe), according to how far the cells depart from normal and how much of the tissue's thickness they fill. Low-grade changes often regress, while high-grade dysplasia is more likely to become invasive cancer; when abnormal cells span the whole epithelium, the lesion is called carcinoma in situ. Dysplasia often arises in tissue that has already undergone metaplasia, as in Barrett's esophagus. In the cervix, persistent human papillomavirus infection causes dysplasia graded as cervical intraepithelial neoplasia, CIN 1 to 3, which Pap and HPV screening aims to detect so that high-grade areas can be removed.

Outside cancer pathology, the word also describes abnormal development of a tissue or organ, as in developmental dysplasia of the hip.