Sir,

Poroid hidradenoma (PH) is a rare benign adnexal tumor of the eccrine sweat glands. It usually presents as a solitary asymptomatic nodule, most commonly at the cephalic extremity.

Herein, we report a case of poroid hidradenoma with atypical localization.

A 63-year-old patient, with a history of hypertension under treatment, presented with a painless tumor on the scrotum existing for five years, which progressively increased in size.

A clinical examination found a polylobed, skin-colored tumor with a pedicled base and an elastic consistency measuring 4 cm in diameter (Fig. 1).

Figure 1: Polylobed pedicled tumor.

Dermoscopy revealed a homogeneous blue area, telangiectasias, and arborized vessels (Fig. 2).

Figure 2: Dermoscopy of the nodule showing a homogeneous blue area, telangiectasias, and arborized vessels.

The patient underwent a biopsy and the excision of the lesion.

The diagnosis of poroid hidradenoma was easily retained on histological examination, showing a pure dermal tumor proliferation, encapsulated, cystic by place, arranged in masses. The tumor cells were monomorphic with eosinophilic cytoplasm (Figs. 3a and 3b).

Figure 3: (a-b) Cystic, encapsulated, pure dermal tumor proliferation with eosinophilic cells.

After one year of follow-up, the patient remained asymptomatic with no signs of recurrence.

Poroid hidradenoma is a rare benign adnexal tumor of the eccrine sweat glands.

It is an uncommon form of eccrine-differentiated hidradenoma according to the WHO classifications of skin tumors, which is itself a rare adnexal tumor [1]. It seems to be more frequent in men than in women, occurring in the sixth and seventh decades of life [2].

Its clinical presentation is nonspecific, in the form of a solitary, asymptomatic, well-circumscribed, red or blue nodule or papule, probably due to the Tyndall effect of the cystic components of the tumor [3]. The surface of the lesion is most often smooth and may occasionally be ulcerated.

The originality of our case lies in the atypical localization. Indeed, the usual localization of poroid hidradenoma is the trunk, thigh, armpits, and limbs [2]. Several cases have been reported in the neck, scalp, back, and vulva [2,4].

The differential diagnosis is made with sweat tumors of dermal nodular architecture (myoepithelioma, mixed tumor, cylindroma, spiradenoma), clear cell tumors (trichilemmoma, metastasis of clear cell carcinoma), and the glomus tumor in its solid form.

Histopathologically, the appearance of the PH is suggestive. It has the architectural characteristics of a hidradenoma, being confined to the dermis without connection to the epidermis and composed of solid and cystic areas, and the cytological characteristics of a poroid neoplasm with small, dark-staining monomorphic poroid cells and larger pale cuticular cells with round to oval uniform nuclei and scanty cytoplasm [5].

However, in the case of doubt, an immunohistochemical study may facilitate the diagnosis, showing the carcinoembryonic antigen (CEA), which is a sensitive marker of cutaneous adnexal tumors and epithelial membrane antigen (EMA), which demonstrates eccrine differentiation. The prognosis of PH is relatively good, with an indolent evolution, yet often unrecognized [6].

Treatment is based on the complete excision of the lesion, which is usually curative. While rare cases of recurrence have been reported in the literature, the emphasis on complete excision remains crucial. Additionally, reported instances of transformation into eccrine porocarcinoma highlight the importance of thorough lesion removal. Despite these considerations, there remains uncertainty regarding the necessity of implementing additional safety margins during excision [7].

Poroid hidradenoma has rarely been reported in the literature. Through our observation, we wish to highlight the interest in complete excision in front of any aspect of a cystic nodule on physical examination or ultrasound.

REFERENCES

1.  Miller R, Ieremia E, Birch J, Chan J. Poroid hidradenoma in the hand:A case report and systematic review. J Cutan Pathol. 2018;45:696-700.

2.  Kumar P, Das A, Savant SS. Poroid hidradenoma:An uncommon cutaneous adnexal neoplasm. Indian J Dermatol. 2017;62:105-7.

3.  Mlika M, Chelly B, Ayadi-Kaddour A, Boudaya S, Kilani T, Mezni FE. Poroid hidradenoma:A case report. Our Dermatol Online. 2012;3:43-5.

4.  Grant MT, Awad MM. Poroid hidradenoma of the scalp in an immunosuppressed patient. J Surg Case Rep. 2019;2019:rjz146.

5.  Chen CC, Chang YT, Liu HN. Clinical and histological characteristics of poroid neoplasms:A study of 25 cases in Taiwan. Int J Dermatol. 2006;45:722-7.

6.  Chiu HH, Lan CC, Wu CS, Chen GS, Tsai KB, Chen PH. A single lesion showing features of pigmented eccrine poroma and poroid hidradenoma. J Cutan Pathol. 2008;35:861-5.

7.  Seo BF, Choi HJ, Jung SN. Eccrine porocarcinoma on the cheek. Arch Craniofac Surg. 2019;20:48-50.