Inverted follicular keratosis (follicular keratoma): causes, symptoms, diagnosis, treatment

The first description of the tumor of inverting follicular keratosis (follicular keratoma) was made by Helwig in 1954. Since then, disputes have not subsided regarding the legitimacy of isolating this neoplasm as an independent nosological entity. A. Mehregan (1983), JM Mascaro (1983) are supporters of the unconditional follicular genesis and recognize follicular keratoma as an independent nosological entity.

W. Lever, G. Schaumburg-Lever (1987), B. Ackerman (1992) consider follicular keratoma as a variant of simple or seborrheic wart. J. T. Headington (1983), H. Z. Lund (1983) are of the opinion that the nosological affiliation of the tumor remains uncertain.

The neoplasm can occur at any age, however, according to V. Ackerman (1992), in 80% of cases the process develops in people over 50 years of age. The tumor occurs somewhat more often in men. The predominant localization is the skin of the face and scalp. It is small painless nodules up to 1 cm in diameter, grayish in color, usually with hyperkeratosis. It is not clinically identified, and most often patients are sent for pathomorphological examination with a diagnosis of vulgar or seborrheic wart, keratopapilloma, less often - basalioma (in case of ulceration).

Pathomorphology of inverting follicular keratosis (follicular keratoma). Microscopically, the tumor is represented by wide, irregularly shaped acanthotic growths of squamous epithelial cells of varying degrees of differentiation. Among them, there are small elongated basaloid cells with hyperchromatic nuclei, as well as large spiny cells with a light nucleus, a clear nucleolus, a wide rim of clear cytoplasm and pronounced intercellular bridges. Between these two types, there are various transitional forms, which determines a certain cellular and structural polymorphism. Basaloid elements are grouped mainly along the periphery of the complexes. In follicular keratoma, diffuse and focal keratinization is expressed, characteristic of the infundibulum of the hair follicle and interfollicular epidermis. An equally characteristic feature is small-focal keratinization in the form of "swirls" - usually small basal or rounded clusters of concentrically grouped epithelial cells that flatten toward the center and contain keratin. Follicular keratoma is also characterized by the presence of fairly large horny cysts, sometimes of irregular configuration, as well as foci of dyskeratosis. Ultrastructurally, the cells of the "swirls" have signs of incomplete keratinization - intercellular desmosomal contacts are few in number, shortened, and located at a considerable distance from each other. Bundles of tonofilaments are shortened, and in the cells of the neutral sections of the formation, bundles of tonofilaments without a specific orientation are noted. Inflammatory infiltrates of a lymphohistiocytic nature are found in the stroma around the tumor growths.

Histogenetically, the tumor is associated with the epithelium of the infundibulum of the hair follicle.

The tumor is differentiated from vulgar and seborrheic warts, keratopapilloma, squamous cell carcinoma, keratoacanthoma, and eccrine poroma. Atypia and polymorphism are found in the focus of squamous cell carcinoma, piloid differentiation is absent in keratoacanthoma and eccrine poroma, and in addition, ductal structures are observed in the eccrine poroma, sometimes filled with homogeneous masses.

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