Trichoepithelioma: causes, symptoms, diagnosis, treatment

Trichoepithelioma (synonyms: Brooke's adenoid cystic epithelioma, superficial trichoblastoma, trichoepitheliomatous nevus, etc.) is a developmental defect of the hair follicle and sweat glands.

Causes and pathogenesis of trichoepithelioma. Trichoepithelioma is believed to develop from a section of the hair follicle with a large accumulation of Merkel cells at the attachment site of the muscle that raises the hair. The disease is familial in 50-75% of cases and is inherited in an autosomal dominant manner. It is often found in women.

Symptoms of trichoepithelioma. Trichoepithelioma is often multiple, occurs mainly in young and adolescent age, is located mainly on the face and trunk. Initially, small-nodular tumor elements, the diameter of which rarely exceeds 0.5 cm, appear on the skin of the nasolabial folds. Gradually, the number of nodules increases, they spread paranasally, capturing the skin of the nose, scalp, auricles, sometimes leading to occlusion of the external auditory canals, neck, interscapular region. In many cases, dominant craniocephalic "epitheliomatosis" is expressed. Sometimes it is observed in combination with cylindroma, since there is a close histogenetic relationship between them. Familial cases are frequent, probably with an autosomal dominant type of inheritance.

Clinically, a distinction is made between simple trichoepithelioma, which can be solitary or multiple, and desmoplastic.

Trichoepithelioma usually develops in childhood or later. Multiple small, usually 2-8 mm in diameter, dense tumor-like elements of hemispherical rounded outlines, the color of normal skin or light pink, appear. Their surface is smooth, but telangiectasias are visible in larger elements. The elements are localized mainly on the face (nasolabial folds, eyelids, upper lip, forehead), in the retroauricular region, on the scalp, less often - in the interscapular region. The elements can be located linearly or have a disseminated character.

Solitary trichoepithelioma is mainly located on the face, more often in its central part. The tumor looks like a papillomatous or fibropapillomatous growth of a dense consistency, pink or flesh-colored, up to 1 cm in size, with a network of dilated capillaries on the surface. The skin around the tumor is not infiltrated. The tumor grows slowly.

In the desmoplastic variety, the elements are rarely multiple. The disease is more common in women and clinically manifests itself as whitish elements with a depression in the center and a dense edge.

In multiple trichoepithelioma, individual tumor elements merge into conglomerates. When localized on the auricles, they cause mechanical occlusion of the auditory canals and subsequently hearing loss. These conglomerates can ulcerate, forming basaliomas. Trichoepithelioma can simultaneously be combined with syringoma, cylindroma.

The combination of multiple trichoepitheliomas and casts is referred to as Brooke-Spiegler syndrome.

Histopathology: There is a well-demarcated intraepidermal tumor or cyst surrounded by a basal cell layer, stromal fibrosis, and focal calcification.

Pathomorphology. Usually, in a limited area under the unchanged epidermis, complexes of various sizes and configurations are visible, the spectrum of which may include primitive "buds" similar to the embryonic stage of the hair follicle, formations of a very bizarre configuration with the presence of structures resembling a partially formed follicle. The cells inside the complexes are clearly squamous epithelial in nature, and are arranged in a palisade-like manner along the periphery. The formation of numerous keratinized structures of the "horny pearl" type is noted. Melanin granules are often found in the keratinization zone. Cases with the presence of less differentiated cell clusters have been described, for example, in the solid type of trichoepithelioma, which is very reminiscent of basalioma. However, in trichoepithelioma, the stromal cellular infiltration consists of fibroblasts, while in basalioma with piloid differentiation, the stromal infiltration along the periphery of the tumor complexes consists of lymphocytes. Trichoepithelioma may also contain tubular (adenoid) structures, which is why this tumor is sometimes called epithelioma adenoides cysticum. In some cases, in addition to cellular complexes, a large number of squamous epithelial cysts are noted. Sometimes the contents of the cysts are subject to calcification.

Histogenesis. The foci of solitary trichoepithelioma consist of relatively immature cells, which makes it similar to basalioma. However, the tendency to form hair follicles distinguishes it from the latter. Electron microscopy revealed that the corneal cysts of trichoepithelioma are immature hair structures in which the cells of the hair matrix directly pass into the corneal cells. Histochemical study using the Gomori method for alkaline phosphatase showed a positive reaction in many invaginations at the periphery of tumor islands and cords, indicating differentiation of hair complexes.

It is quite difficult to distinguish this tumor from basalioma with piloid differentiation, but the reaction to alkaline phosphatase helps in this, indicating the presence of rudimentary hair complexes in the trichoepithelioma.

Differential diagnosis. The disease should be distinguished from Pringle-Bournevel disease, syringoma and basalioma.

Treatment of trichoepithelioma. Application of cytostatic ointments (30% prospedin, 5% fluorouracil, etc.) has a good effect. Cryodestruction, electrocoagulation, surgical method, carbon dioxide laser are used to remove large nodes.