Table 1.

Microscopic attributes of actinic keratosis.

Attribute number	Name	Definition	Location	References
1	Hyperkeratosis	Thickness of the stratum corneum greater than 15 micrometers. Refractable and amorphous structures in the stratum corneum	Epidermis, horny layer (stratum corneum)	(53, 54)
2	Parakeratosis	Presence of nucleated cells in the stratum corneum due to the incomplete keratinization process on the surface of the skin	Epidermis, horny layer (stratum corneum)	(53, 54)
3	Desquamation of the stratum corneum and corneocyte cohesion	Junction of corneocytes forming scattered plaques. Presence of “chunks” of scattered corneocyte clusters	Epidermis, horny layer (stratum corneum)	(55)
4	Cellular atypia in the viable epidermis	Disorder in the shape of the cluster of cells of the stratum granulosum and stratum espinosum	Epidermis, granulous layer (stratum granulosum), and spinous layer (stratum spinosum)	(38, 56–60)
5	Dyskeratosis	Presence of rounded nucleated cells in the stratum espinosum	Epidermis, spinous layer (stratum spinosum)	(54)
6	Inflammatory (dendritic) cells in the epidermis	Presence of rounded and refractile cells, appearing in small groups in the stratum espinosum	Epidermis, spinous layer (stratum spinosum)	(38, 55, 57)
7	Nuclear pleomorphism in the stratum espinosum	Variations in the size and shape of cells and nuclei in the stratum spinosum	Epidermis, spinous layer (stratum spinosum)	(38)
8	Atypical keratinocytes with follicular coverage	Dark openings with great refraction of surrounding cells	Epidermis, spinous layer (stratum spinosum), and basal layer	(61)
9	Poorly defined boundaries between keratinocytes	Irregular connections between keratinocytes	Epidermis, spinous layer (stratum spinosum), and basal layer	(56)
10	Inflammatory cells in the basal layer	Presence of small and scattered refractable cells in the basal layer	Epidermis, basal layer	(55)
11	Cellular apoptosis in the viable epidermis	Presence of cell death in spots of the epidermis darkened cytoplasm, and bright nucleus	Epidermis	(38, 55, 57)
12	Fibers around the dermal papillae	Presence of a tangle of fibers and dense material around the papillae. Poorly defined papillae	Dermis, papillary layer	(58)
13	Papillary irregularity	Poorly defined dermal papillae surrounded by dense material	Dermis, papillary layer	(58)
14	Rounding of blood vessels in the papillary dermis	Rounded blood vessels traversing the papillae. Refractive cells = blood cells	Dermis, papillary layer	(38, 62)
15	Melanocytes clustered in the dermis	Bulky cells	Dermis	(58)
16	Solar elastosis	Degradation of elastic and collagen fibers in the skin	Dermis	(54)
17	Brain-like, finger-like appearance	Clusters of rounded, misshapen cells	Dermis	(54)
18	Dermal nests	Cell clusters	Dermis	(54, 58)