Poroid Hidradenoma: A Two-Case Report and Literature Review

Abstract

Poroid hidradenoma (PH) is a rare benign tumor that shows differentiation of the eccrine sweat gland. It occurs mainly in adults, presenting as a 0.5 to 2 cm-sized intradermal nodule, mostly on the head, extremities, trunk and neck. We report two rare cases of PH, one on the face and the other on the heel. The first patient was a 50-year-old male who had a solitary, skin-colored nodule on his right temple for 6 months. The second patient was a 67-year-old female who presented with a solitary, bean-sized, tender nodule on her left heel for 1 year. The common histological examination finding was a well-circumscribed tumor composed of solid portions and large cystic spaces in the center. The tumor cells consisted of small, monomorphic poroid cells and large cuticular cells in both cases. To our knowledge, only few cases of PH have been reported. Herein, we report two rare cases of PHs with literature review.

INTRODUCTION

Poroid hidradenoma (PH) is a benign neoplasm with eccrine differentiation¹. Typically, PH is a solitary tender nodule with a diameter ranging from 0.5 to 2 cm. It appears skin-colored or slightly reddish, but the presence of cystic parts may confer a blue color on the lesion. It has both solid and cystic components and is restricted within the dermis². We present rare cases of PH in two patients.

CASE REPORT

Case 1

A 50-year-old male presented with a solitary skin-colored nodule on his right temple. The patient recalled first noticing the lesion 6 months before. The lesion had increased in size, but the patient did not complain of tenderness or other subjective symptoms. He had a history of nephrotic syndrome and no history of trauma in the area of the skin lesion. He had no relevant social and family histories. Physical examination revealed a bean-sized, skin-colored, indurated nodule arising from the right temple (Fig. 1A).

Fig. 1. (A) Case 1: A 50-year-old male with a solitary skin-colored nodule on the right temple. (B) Case 2: A 67-year-old female with a 1.5 cm-sized, bluish indurated nodule arising from her left heel.

Case 2

The second case was a 67-year-old female who presented with a solitary tender nodule on her left heel. The lesion had appeared 1 year prior and slowly enlarged over 3 months. The patient had a history of hypertension and no history of trauma in her skin lesion. She had no relevant social and family histories. Physical examination revealed a 1.5 cm-sized, bluish indurated nodule arising from the left heel (Fig. 1B).

Histological examination of two specimens revealed well-circumscribed tumors composed of solid portions and large cystic spaces. Tumors were confined entirely to the dermis and no epidermal connection could be seen. Ductal lumens were filled with eosinophilic materials, They consisted of smaller monomorphic poroid cells with round-to-oval nuclei and larger cuticular cells with a pale cytoplasm in both cases (Fig. 2). In an immunohistochemical study, carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) were both positive in the solid portions and ductal structures in the first case. In the second case, only EMA was positive (Fig. 2). We received the patient's consent form about publishing all photographic materials.

Fig. 2. (A~D) Case 1. (E~H) Case 2. (A) A well-circumscribed tumor composed of solid and cystic components in the mid-dermis and no epidermal connection could be seen (H&E, ×40). (B) Ductal structures are lined by cuticular cells and some poroid cells could be observed (H&E, ×200). (C) A tumor showed positive for epithelial membrane antigen (EMA; ×40). (D) A tumor showed positive for carcinoembryonic antigen (CEA; ×40). (E) A tumor composed of soild and cystic components with no epidermal connection (H&E, ×40). (F) Poroid cells and cuticular cells were mixed in the solid portion of tumors and ductal lumens were filled with eosinophilic materials (H&E, ×200). (G) A tumor showed positive for EMA (×40). (H) A tumor showed negative for CEA (×40).

DISCUSSION

PH is a form of hidradenoma with eccrine differentiation according to the WHO classifications of skin tumors¹. The age of onset ranges widely, with a peak incidence in the seventh decade of life³. No sex or ethnic predilection was reported. The most predominant site of involvement is the head and neck region, followed by the axilla, trunk, and extremities⁴. Miller et al.¹ reported the systematic reviews of PH, which occur more commonly in male, in the head and neck region or limbs. Considering that these neoplasms can be generally asymptomatic or accompanied by mild tenderness, the incidence of PHs might be underestimated in the literature⁵.

Hidradenomas have traditionally been considered to exhibit eccrine differentiation based on histochemical and electron microscopic features². However, recently, subclassification of hidradenomas into two groups, those with apocrine differentiation (known as clear cell hidradenoma) and those exhibiting eccrine differentiation (known as PH), was suggetsted⁶. The former accounts for 95% of all hidradenomas and is composed of clear, polygonal, and mucinous cells with apocrine differentiation. The latter neoplasm, which constitutes 5% of hidradenomas, is characterized by a single or multilobulated dermal nodule with no connection to the epidermis and consists of two cell types, poroid and cuticular cells with eccrine differentiation.

Histopathological examination revealed that PH presents solid and cystic components, and tumor cells restricted to the dermis⁷. The tumor is composed of two types of cells, poroid and cuticular cells. Poroid cells are uniform, small cuboidal cells with an oval-to-round nuclei. Cuticular cells have an abundant eosinophilic cytoplasm with a larger nucleus that shows occasional multinucleation. The cystic spaces are considered as eccrine dilated ducts containing eccrine secretory fluid.

In immunohistochemical studies, epithelial markers such as EMA and cytokeratin are considered related to the cells of the dermal sweat ducts⁵. EMA demonstrates eccrine differentiation⁷. CEA, a sensitive marker of cutaneous adnexal tumors, can also be positive.

The distribution of the lesions varied between the tumor groups. In our literature review, PHs are mostly predominant in the trunk and are not found on the plantar aspect of the foot (Table 1)². A second patient with PH in the plantar area of the foot will be the rare case worldwide.

Table 1. The locations of patients with poroid hidradenoma worldwide including our cases.

Site of the lesion	Number (%)
Trunk	21 (33)
Upper limb	13 (21)
Palm	0 (0)
Lower limb	11 (17)
Plantar aspect of foot (our case)	1 (1)
Head and neck (our case)	12 (19)
Another site	4 (6)

PHs are mostly covered with intact skin; however, approximately 15% of these neoplasms demonstrate ulceration at presentation due to direct trauma or abrasion to the mass². PHs can have a bluish aspect, probably due to the Tyndall effect of the cystic components within the tumors⁵. This confounds the clinician in distinguishing between PH, angioma, melanoma and nevus.

The differential diagnosis of PH includes other poromas (hidroacanthoma simplex, dermal duct tumor, eccrine poroma) and apocrine hidradenomas⁸. Hidroacanthoma simplex is characterized by nests of round cells within normal epidermal cells. Dermal duct tumor is same histopathologic features, but located in the dermis. Eccrine poroma is clear margin between normal epidermal keratinocytes and cuboidal cells with dark nuclei protrudes into the underlying dermis. Apocrine hidradenomas are characterized by mucinous, polygonal and clear cells, and decapitation secretion into the ducts with apocrine differentiation⁸. In addition, some benign subcutaneous neoplasms such as fibroma, fibrolipoma, dermatofibroma, hemangioma, pyogenic granuloma, epidermal cyst, and basal cell epithelioma might be confused with this neoplasm⁸. Therefore, histological examination with a skin biopsy is crucial for the diagnosis of PH.

PH is treated with total excision of the lesion, which is usually curative. These neoplasms are considered benign, because the risk of malignant transformation is less than 1%⁹. Furthermore, the prognosis of PH is relatively good, and recurrence has rarely been reported². Our patients had no complications or recurrence 3 months after the excision.

Until now, only few cases of PHs have been reported. Since 1990, rare cases of PHs have been reported in the literature and only 3 case reports have been published in Korea (Table 2)¹⁰,¹¹,¹². In these reports, the clinical features of patients were similar with those of our patients, except the anatomical sites (thigh, shin, back). Herein, we report two rare cases of PHs.

Table 2. Previous reported cases of poroid hidradenomas in Korean literature.

Case no.	Age (yr)/sex	Trauma history	Duration (yr)	Clinical feature	Site	Author
1	51/Female	-	1	A solitary bluish nodule	Right thigh	Park et al. (2005)10
2	55/Female	-	3	A solitary bluish nodule	Left shin	Kim et al. (2007)11
3	79/Female	-	1	A solitary reddish to bluish nodule	Back	Kim et al. (2015)12
Our case 1	50/Male	-	0.5	A solitary skin-colored nodule	Right temple
Our case 2	67/Female	-	1	A solitary bluish nodule	Left heel

DATA SHARING STATEMENT

Research data are not shared.