1, Etiology
It is generally believed that eccrine adenomas occur in large eccrine glands, but it is unknown whether they originate from the apocrine secretory glands or the stem gland structure. The reasons supporting their occurrence in large eccrine glands are: apocrine cells have no secretory function before puberty and only have secretory function during puberty, and eccrine adenomas indeed do not occur before puberty, but there are still some points that cannot be explained, such as the armpits, areola, and pubic area, which have an extremely rich number of apocrine cells, and there are also a small number of apocrine cells in the eccrine glands, but eccrine adenomas occur very rarely. Moreover, the apocrine sweat glands of blacks3times higher than whites, and their incidence should also increase accordingly, but literature reports that the incidence in blacks is actually lower.
There is also controversy about the origin of eccrine adenomas in the labia minora. If the eccrine adenoma originates from the apocrine cell stem, then hair follicles should be found nearby, but they are often difficult to find in the labia minora. Woodworth studied these glands and found that they are larger than the general eccrine glands in the skin and smaller than the apocrine glands. They can be distinguished by Prussian blue staining as eccrine gland cells or apocrine cells, because apocrine cells contain iron components, while eccrine gland cells do not. The author confirmed that the eccrine epithelial cells in the labia minora do not contain iron. Therefore, some people believe that the origin of eccrine adenomas in the labia minora is neither the eccrine gland nor the large eccrine gland, but rather another type of gland between the two, which is unique to the labia minora.
2, Pathogenesis
The tumor is generally a single, round, solid nodule, soft in texture, covered with normal skin. Occasionally, it may ulcerate, invert, and form a reddish-brown papillomatous mass, which is prone to bleeding and resembles cancerous or inflammatory granulation. The tumor is located in the superficial dermis, close to the epidermis, with a diameter of 0.1~1cm, with an average of 0.8cm, with clear boundaries.
Under the microscope, the morphology is similar to that of papillomas of large ducts in the breast, with many tubular or cystic cavities visible within the tumor, containing interlocking papillary protrusions. The surface has two layers of cells, namely the cavity wall and papilla, which are often lined with a single layer of large eccrine-type high columnar cells. The nuclei are large, palely stained, and the cytoplasm is eosinophilic, often with apocrine secretion; there is also a layer of discontinuously arranged cuboidal epithelial cells around the periphery.