Hidradenoma papilliferum is a rare benign tumor of the genital and perianal regions. It is most commonly located on the vulva, although extragenital locations have been described. It has a predilection for women in the fourth and fifth decades of life. Typically, these are small tumors a few millimeters in diameter, but some large tumors have been described. There is no connection to the overlying epidermis or mucosa.
Clinical Findings: Hidradenoma papilliferum is an extremely rare benign tumor located in the dermis. It seen almost exclusively in middle-aged women. The lesions are almost always located in the genital region. They typically manifest as asymptomatic nodules that are discovered incidentally. There are usually no overlying epidermal changes, and the tumor is well circumscribed, freely movable, and firm in consistency. They do not have a connection with the overlying epithelium. In rare instances, they can be tender or pruritic and can bleed or ulcerate. Most of these tumors are found on routine gynecological examination. The most common location is the labia majora. The differential diagnosis of a solitary, firm dermal nodule in the genital region is very broad, and a biopsy for histopathological examination is required in all cases to make the diagnosis. It is essential for dermatologists and gynecologists to be aware of this tumor and the common locations in which it is found.
Pathogenesis: Hidradenoma papilliferum is a tumor that is believed to be derived from apocrine tissue. For this reason, it is considered to be a type of apocrine adenoma. Apocrine glands are found in higher density in the anogenital region, and that may be one reason for the unequal cutaneous distribution of this tumor. The tumor is benign and is closely related to another benign adnexal tumor, the syringocystadenoma papilliferum. The latter tumor is more common on the head and neck, with a predilection for the scalp. Histologically, these two tumors are almost identical, with the major differentiating factor being that the syringocystadenoma papilliferum has a connection to the overlying epidermis. Clinically, the syringocystadenoma papilliferum usually manifest as an ulcerated papule or plaque. Both of these tumors can develop within a nevus sebaceus.
Histology: Hidradenoma papilliferum is a well circumscribed dermal tumor. It almost never has any overlying epithelial abnormalities. The syringocystadenoma papilliferum, on other hand, has a connection with the overlying epidermis. They both commonly arise in conjunction with a nevus sebaceus. On closer inspection, the hidradenoma papilliferum is composed of vascular papillary projections into the center of the tumor lobule. These projections are lined by cells with an apocrine origin that have a columnar configuration. Apocrine secretion (decapitation secretion) is often noted in various sections of the tumor. There is also a thin layer of myoepithelial cells. Within the papillary projections is a background stroma composed of many vascular spaces and lymphocytes.
Syringocystadenoma papilliferum has almost identical central characteristics. Compared with the hidradenoma papilliferum, it has a more dense plasma cell infiltrate and has an attachment to the overlying epidermis, which usually manifests as an invagination of the epidermis into the tumor lobule.
Treatment: A complete excision is diagnostic and curative at the same time. Often, a biopsy is performed to ascertain the diagnosis, followed by the curative complete excision. These are rare and benign tumors. There have been reports of malignant degeneration, but this is exceedingly rare.