in comparison with the control tissue , tretinoin-treated tissue examined by light and electron microscopy showed the following effects : replacement of the atrophic epidermis by hyperplasia , elimination of dysplasia and atypia , eradication of microscopic actinic keratoses , uniform dispersion of melanin granules , new collagen formation in the papillary dermis , new vessel formation ( angiogenesis ) , and exfoliation of retained horn in the follicles .
C0014520
epidermis
C0022602
actinic keratoses