Intraepithelial

Intraepithelial describes something that is located within the epithelium, the tissue that lines surfaces and cavities of the body. The epithelium sits on a basement membrane, and intraepithelial means that a process or substance occurs entirely within that epithelial layer, without penetrating into the underlying connective tissue or stroma.

In pathology, intraepithelial is used to characterize lesions and disorders that remain confined to the epithelial layer. A common context is intraepithelial neoplasia, where abnormal cells are present within the epithelium but have not invaded through the basement membrane. Examples include cervical intraepithelial neoplasia (CIN) and anal intraepithelial neoplasia (AIN). The term helps distinguish these conditions from invasive carcinomas, in which malignant cells breach the basement membrane and invade underlying tissues.

Intraepithelial lymphocytes are another widely used concept, referring to immune cells that reside within the epithelial layer, particularly in mucosal tissues. These intraepithelial lymphocytes participate in immune surveillance and respond to antigens encountered at epithelial surfaces. Their numbers and activity can change in various diseases, including infections and inflammatory conditions.

Clinically, recognizing intraepithelial involvement informs diagnosis, prognosis, and management. Lesions limited to the epithelium may be monitored or treated with procedures aimed at removing or destroying dysplastic epithelium, while invasion into the underlying tissue typically requires more extensive therapy. The term is applicable across different epithelia, including skin and mucosal surfaces.