Keratoacanthoma: causes, symptoms, diagnosis, treatment

Keratoacanthoma (syn.: molluscum pseudocarcinomatosum, molluscum sebaceum, tumor-like keratosis) is a rapidly growing benign tumor, in the development of which significance is given to viral infection, immune disorders, long-term exposure to various unfavorable, mainly exogenous, factors (trauma, ionizing radiation, mineral oils, tar, insolation, etc.).

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Causes of Keratoacanthoma

According to G. Burg (2000), viral particles detected at the ultrastructural level and the presence of human papillomavirus DNA type 25 were found in almost half of the cases of solitary keratoacanthoma. The latter variant is the most common, multiple elements are observed less frequently.

Multiple keratoacanthomas are often familial, inherited in an autosomal dominant manner, and may be a manifestation of paraneoplasia in cancer of internal organs, especially the digestive tract (Torre syndrome).

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Histogenesis

The histological picture is similar to that of solitary keratoacanthoma, but the proliferative process and atypia are less pronounced and a connection with the epithelium of the hair follicle openings can be clearly seen.

It is considered proven that keratoacanthoma arises from hyperplastic epithelium of the infundibulum of one or more closely located hair follicles and associated sebaceous glands.

Symptoms of Keratoacanthoma

The tumor is typically localized on exposed parts of the body and limbs, especially on the extensor surfaces, mainly in elderly people. The tumor has the appearance of a round or oval exophytic node on a wide base, reddish, sometimes with a bluish tint or the color of normal skin, 2-3 cm or more in diameter. The central part of the tumor is filled with horny masses, the marginal zone is in the form of a high ridge. After the active growth phase, a stabilization phase usually occurs, during which the tumor does not change in size, then after 6-9 months - a phase of spontaneous regression with the disappearance of the tumor node and the formation of an atrophic scar. In some cases, the stabilization phase does not occur and the tumor can reach gigantic sizes - up to 10-20 cm in diameter - and transform into squamous cell carcinoma. Keratoacanthomas of unusual localization have also been described - subungual, on the mucous membranes of the lips, cheeks, hard palate, conjunctiva, and nose.

In the development of keratoacanthoma, three stages are distinguished, each with a characteristic histological picture. In stage I (stage A), a depression in the epidermis filled with horny masses is observed. In the lateral sections, the horny masses are surrounded by a duplication of the epidermis in the form of a "collar". From the base of the keratotic plug, epidermal strands extend into the underlying dermis, containing cells with hyperchromic nuclei. The basement membrane zone is preserved. In stage II (stage B), pronounced epithelial hyperplasia is detected at the base of the crater, as a result of which the epithelial outgrowths penetrate deep into the dermis. The cells of the Malpighian layer are usually pale in color, larger than normal, mitoses and dyskeratosis are sometimes visible. Signs of cellular atypia, polymorphism are found in the epidermal outgrowths, their lower border is not always clear. In the dermis there is edema, inflammatory reaction with infiltration by lymphocytes, neutrophilic and eosinophilic granulocytes with an admixture of plasma cells. Infiltrate cells sometimes penetrate into epidermal outgrowths. Such a picture can be considered as nrecancer. In stage III (stage C) there is a violation of the integrity of the banal membrane with the proliferation of epidermal outgrowths deep into the dermis and the phenomena of pinching off complexes of squamous epithelial cells. Polymorphism and hyperchromatosis increase, dyskeratosis is replaced by pathological keratinization with the formation of "horny pearls", all the signs of squamous cell cancer with keratinization appear. At the base of the lesion there is a dense inflammatory infiltrate.

With regression of keratoacanthoma, possible in stages I-II, the corneal plug decreases, the structure of the basal layer normalizes, signs of hyperproliferation of the epidermis disappear, and a large number of fibroblasts appear in the infiltrate with the final formation of a scar.

Multiple keratoacanthoma can be observed both in the form of sequentially appearing nodules, and in the form of several foci appearing simultaneously. In the nervous variant, the elements appear gradually on various areas of the skin, but especially on the face and extremities. They are represented by papules and nodes with a depression in the center filled with horny masses, resolving within a few months with the formation of atrophic scars. In the second variant, many large follicular papules with a diameter of 2-3 mm appear simultaneously.

Diagnosis of keratoacanthoma

Keratoacanthoma must be differentiated from the initial stage of squamous cell carcinoma. The most important differential diagnostic features are the presence of a crater-shaped (mollusk-like) structure in keratoacanthoma and the absence of nuclear atypia. It differs from molluscum contagiosum by the absence of molluscum bodies.

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