suprabasal

Suprabasal is a term used in histology and pathology to describe cells or regions of a stratified squamous epithelium that lie above the basal cell layer, i.e., above the basement membrane. It contrasts with the basal layer, where cells proliferate and attach to the basement membrane.

In normal skin and mucosal epithelia, keratinocytes originate in the basal layer (stratum basale) and gradually differentiate as they migrate upward through the spinous layer (stratum spinosum) and granular layer (stratum granulosum). Suprabasal cells are thus more differentiated than basal cells. In thick skin, the stratum lucidum also lies in the suprabasal position. Ultimately, cells in the more superficial layers become cornified in the stratum corneum. In healthy tissue, mitotic activity is typically confined to the basal layer.

In pathology, the term suprabasal is used to describe abnormal patterns of proliferation, differentiation, or invasion that involve layers above the basal layer. For example, suprabasal dysplasia or suprabasal mitotic activity indicates that atypical cells or sustained division occur in layers above the basement membrane, which can have diagnostic or prognostic implications. Conditions such as psoriasis may exhibit hyperplasia with increased cell production in suprabasal layers, while invasive carcinomas may breach the basement membrane and extend beyond the basal region into more superficial layers.

The concept of suprabasal helps pathologists characterize the layer of origin or involvement in epithelial lesions and is applicable to various stratified squamous epithelia, including skin and mucosa.