Differential diagnosis of melanocytic nevi and squamous papillomas of dogs

Abstract

The difficulties of differential diagnosis in the clinical practice of a veterinarian are mainly associated with skin tumors. The article presents the differential criteria of squamouscellpapillomasandmelanocyticnevi, clinically diagnosedaspapillomas. Clinical and morphological identity of papillomas and nevi is in the features of growth in the form of warts (exophytic growth), signs of hyperpigmentation (color from light to dark brown). The exclusive criterion of melanocytic nevi is the presence of hair on the surface of the tumor, which is not typical for papillomas. Squamous cell papillomas and melanocytic nevi have epidermal origin, this feature determines their clinical and morphological similarity, as well as the stages of growth. Nevi arise from melanocytes basal layer of the epidermis, the active proliferation of which contributes to the replacement of keratinocytes of the epidermis. Melanocytes infiltrate all layers, signs of hyperkeratosis and parakeratosis are not noted. In the thickness of the dermis, melanocytic infiltration is observed, melanocytes are polymorphic, but retain the features of the structure in the form of split cytoplasm. Nevus contains hair follicles and sebaceous glands with signs of destruction on the background of compression of tumor tissue. Melanocytes of the epidermis are larger, their location provides a zonal structure of the nevus, highlighting the epidermis layer and the reticular layer infiltrated by smaller melanocytes. Papillomas are formed due to the proliferation of basal cells, which are characterized by all stages of differentiation as the growth of tumors and the advancement of cells to the stratum corneum of the epidermis. Coylocytic atypia is the differential criterion for the histological diagnosis of papillomas. The basal membrane is preserved in both melanocytic nevi and squamous cell papillomas, there are signs of cellular atypism and acanthosis.