Pilomatricoma: causes, symptoms, diagnosis, treatment

Pilomatricoma (syn. Malherbe's necrotizing calcified epithelioma) is most often found in childhood and adolescence, mainly on the face or in the shoulder girdle, as a solitary tumor reaching several centimeters in size, often covered by normal skin with a smooth surface protruding above the skin level, of very dense consistency. It grows slowly over many years, does not ulcerate. Sometimes familial cases are observed.

Pathomorphology of pilomatricoma. A characteristic feature of pilomatricoma in the early stages of development is the presence of massive layers of small round cells with dark basophilic nuclei and virtually indistinguishable cytoplasm - typical cells of the hair matrix. Within these clusters, islands of gradual transformation of matrix cells into larger cells with pale-colored cytoplasm with unclear boundaries and pycnotic, gradually disappearing nuclei are visible, due to which they are called shadow cells. The tumor stroma in the early stages is rich in vessels. In more mature formations, clusters of shadow cells are observed, the vascular component is poorly expressed, dystrophic processes with the presence of giant multinuclear macrophages and calcium salt deposits predominate, which are in the form of small granular masses in the shadow cells or are located in the form of amorphous masses revealed by the Kossa method. Ossification is observed in 15-20% of cases. Among the dystrophic islands of pale-colored cells, clusters of immature keratin are often found, as well as pigmented cells of the hair follicle. Sometimes, pilomatricoma may arise in the wall of a pilar cyst.

Histogenesis of pilomatricoma. Histochemical examination and electron microscopy revealed that basaloid cells are cells of immature hair matrix. A sharply positive reaction to SS and SH groups in most tumor cells and double refraction of shadow cells in a polarizing microscope indicate a tendency of tumor cells to keratinization. Transitional cellular elements between matrix cells and shadow cells are analogous to those in normal hair keratinization; they contain a large number of tonofibrils and the keratohyalin stage of keratinization is absent.

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