Benign Neoplasms Neoplasms of Dermal Appendages

Papillary Hidradenoma (Hidradenoma Papilliferum)

Hidradenomas are benign sweat gland tumors that may raise the issue of malignancy with both clinicians and pathologists (Fig. 10A and B). The clinician may observe a flesh-colored or blue nodular lesion, frequently with central umbilication, usually less than 1 cm. Hidradenomas may become ulcerated, exposing bright red papillary tissue (22), hence raising the concern for malignancy. Histologically, the lesion is composed of tightly packed cystic and glandular spaces lined by a two-cell layer, an inner cuboidal and an outer myoepithelial cell layer. The tightly packed glands may mislead the observer to consider an adenocarcinoma; however, closer observation shows the characteristic apocrine "snouts" of the inner layer, and the presence of the myoepithelial layer, confirming the true nature of the lesion, which may also be found in the axilla (Table 10).


Trichoepitheliomas and other related adnexal neoplasms of hair follicles (trichoblas-toma, trichodiscoma, trichomyxoma, trichofibroma, and trichofolliculoma) are

Table 9 Micropapillomatosis Labialis



Clinical appearance

Differential diagnosis




Multiple small uniform



tosis labialis

papillary projections of



inner labia minor/introitus

Introitus Folliculitis

Figure 10 Hidradenoma. (A) Low-power view shows a well-circumscribed lesion. (B) On higher power, the spaces are seen to be lined by a double layer, inner epithelial and outer myoepithelial.

benign tumors (Fig. 11A and B). They may rarely occur on the vulva (23,24). Trichoepitheliomas may be single or multiple and are usually less than 1 cm, flesh-colored papules or nodules (25). They may be seen on histologic section to arise from hair follicles, in which case invasion may be mistakenly diagnosed. The lesions may be confused with basal cell carcinomas because of the similarity of cell type; however, trichoepitheliomas lack ulceration or inflammatory tissue reaction and are often associated with keratinous cysts (25). Trichoepitheliomas may also raise concern of malignancy because of the active mitotic rates that may be present (Table 11) (23).


Syringomas are benign neoplasms of eccrine sweat glands (Fig. 12). The lesions are small and frequently multiple, flesh-colored papular lesions that may occur in a variety of locations (26). When on the labia majora, they are frequently bilateral. Histologically, they are composed of intradermal solid or cystic nests of epithelial cells. Cystic spaces may be lined by one or two layers of flat-to-cuboidal pale cells (22). The lesions often have a characteristic comma shape (Table 12).

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