SkIndia Quiz 25: A solitary nodule on the right buttock.

REPORT OF A CASE

A 31-year-old otherwise healthy female presented with a six month history of a slowly growing solitary nodule on her right buttock. On physical examination there was a solitary firm, fixed, red to violaceous nodule with a diameter of 5 mm × 8 mm on the right buttock [Figure 1]. The overlying skin appeared slightly eroded with some surface maceration. There was a history of occasional bleeding with minor trauma, but no history of tenderness was mentioned. Physical examination was unremarkable. The lesion was completely excised and sent for histological examination.

Figure 1

Solitary small red to violaceous nodule on the right buttock

MICROSCOPIC FINDINGS AND CLINICAL COURSE

Histological examination demonstrates a solitary, dilated, cystic, dermal nodule with papillary projections toward the luminal spaces. The lumina was lined with a double layer of cells consisting of an inner layer of secretory cells and an outer layer of small cuboidal cells. A portion of the luminal cells showed evidence of decapitation secretion. The tumor was completely separated from the epidermal surface [Figures 2–4].

Figure 2

Tumor is surrounded by a fibrous capsule of connective tissue and composed of cystic space and papillary projections (H and E, ×40)

Figure 4

The inner columnar cells show evidence of active decapitation secretion. (H and E, ×400)

Cystic and tubular structures lined with double layer of cells (H and E, ×100)

ANSWER

Diagnosis: Ectopic hidradenoma papilliferum.

Hidradenoma papilliferum (HP) is a rare, benign, cystic papillary tumor[1] originating from the apocrine gland. The tumor typically presents in the third to fifth decades of life; there is a lack of reports of HP ocurring prior to puberty, thought to be related to expression of estrogen receptors found in the tumor. HP is most commonly reported in the anogenital region, particularly the vulva, of caucasian women.[2] There is only a single report of a perianal HP occurring in a male.[3] The anogenital predilection of HP is thought to be associated with the increased abundance of regional apocrine sweat glands, particularly the mammary-like glands;[4] 90% of papillary hidradenomas and the majority of anogenital sweat glands express estrogen and progesterone receptors. Interestingly these receptors represent a reliable marker for differentiating anogenital sweat glands from classic apocrine sweat glands and explains why papillary hidradenomas occur almost exclusively in the female anogenital region.[5]

When the tumor arises in nonanogenital regions, it is referred to as an ectopic HP. Ectopic HP typically occurs in older patients, with a 1:1 male to female ratio. Most cases occur in the external ear and eyelid where there are apocrine glands;[1] other sites such as the forehead, face, postauricular area, scalp, axillae, arm, thigh and back have also been reported.[3] Interestingly, there are no previously reported cases of ectopic HP presenting over the buttock.

Hidradenoma papilliferum present as a red, firm well circumscribed solitary nodules of approximately 0.5 cm in diameter.[13] Although infrequent, multiple lesions may appear in a unilateral distribution with an incidence of 5%.[4] Frequently, these tumors are asymptomatic,[1] although some may become tender and ulcerate. Bleeding with minor trauma may also occur. Elevated lesions tend to be cystic and umblicated. Duration of lesions was reported to vary from one year to six years before histological diagnosis was established.[3]

There are four histological subtypes of HP: Tubular, cystic, papillary and syringocystadenoma papilliferum-like.[4] Microscopic examination usually demonstrates a well-circumscribed solitary subcutaneous tumor surrounded by a fibrous capsule, with a cystic and tubular component. The cystic lumina is typically lined by a double or single layer of cells with basal cuboidal myoepithelial cells, and apical secretory cells. The apical cells commonly display a conspicuous “decapitation” pattern,[1] as was depicted in our case. The presence of active decapitation secretion in HP highlights the apocrine origin of the tumor.[2] Syringocysadenoma papilliferum, an important differential, presents as a cystic invagination extending downward from the epidermis with numerous papillary projections and invaginations of the cyst wall. Syringocystadenoma papilliferum is directly connected to the epidermal surface, differentiating it from HP. Other tumors in differential diagnosis of HP are tubular apocrine adenoma and clear cell (apocrine) hidradenoma.[1]

Malignant transformation in HP is rare, although focal areas of squamous metaplasia may occur. HP generally has a favorable prognosis and there is a low risk of recurrences with surgical excision, the treatment of choice for both anogenital and ectopic HP.[12]