Poroid Hidradenoma: Case Report and Comprehensive Review of the Literature

Cutaneous adnexal tumors are benign or malignant growths of one of the four normal skin appendages: hair follicles, sebaceous glands, apocrine glands, and eccrine glands. They are classified based on morphological differentiation toward one or more of the listed adnexal structures [1]. Sweat gland tumors, both eccrine and apocrine, are generally considered an uncommon group of benign adnexal neoplasms with a wide histological spectrum [2]. One subcategory of sweat gland tumors is the poroid tumors, including hidroacanthoma simplex, classic poroma, dermal duct tumor, and poroid hidradenoma (PH) [3]. Poroid tumors are characterized by poroid cells which are small round, monomorphous cells with small amounts of cytoplasm that exhibit ductal differentiation (Fig. 1). Here, we further describe the poroid hidradenoma which displays a hybrid of the architectural features of a hidradenoma, namely, tumor cells are entirely intradermal with solid and cystic components and nodular deep expansile growth, but the cytologic characteristics of a poroid neoplasm, meaning they contain predominantly poroid and cuticular cells akin to the small round cells that make up normal eccrine ducts [4, 5].

Although originally described in 1990 [6], the benign adnexal neoplasm PH is understood to be a rare diagnosis in the literature. Therefore, currently no official guidelines exist for its management, and minimal information is accessible regarding PH’s true incidence, natural clinical history, or treatment outcomes. These cutaneous tumors develop primarily from eccrine sweat glands and represent the newest variant of eccrine gland neoplasms [5]. They typically present as a painless, well-circumscribed solitary nodule or papule that often grows over the course of months to years and can have associated itching or mild tenderness [4, 7, 8]. PH can affect a wide range of ages, but with a predilection for the sixth to seventh decade [4]. It has been reported that PHs were most frequently located on the head and neck [7]. However, a systematic review outlining all published cases between 1990 and 2017 [8] demonstrated that nearly 40% of published PHs were on the head and neck, and an equal number (∼40%) of cases were situated on the limbs. The case presented here is that of a PH on the posterior shoulder in a 67-year-old woman. Additionally, we have included a systematic review of the literature describing PH including its presentation, patient demographics, treatment, recurrence, and outcomes (see Table 1 for a comprehensive list of all published reports of PH).

The patient is a 67-year-old woman with an extensive past medical history including (but not limited to) diabetes, cirrhosis, hyperlipidemia, hypertension, hypothyroidism, multinodular goiter, memory loss, chronic joint and low back pain, and iron and vitamin deficiencies secondary to gastric bypass surgery, presenting with a right posterior shoulder lesion. The patient first noticed the lesion 5 years prior and initially described it as a flat, red, scaly lesion. Over the course of 1 year, the lesion increased in size and began to have some concurrent drainage. Over the preceding 5-months, the lesion also changed in color from red to purple. The patient did not have complains of itching and burning at the site of the lesion and denies any associated pain or weight loss. There was no personal or family history of skin cancer.

On physical exam, a 5-mm diameter, light brown, irregular but well-circumscribed lesion was observed on the right posterior shoulder (Fig. 2). Shave biopsy to the level of the dermis was performed and specimen was sent for pathology in formalin. The skin fragment measuring 0.9 × 0.7 × 0.3 cm revealed an adnexal neoplasm extending to the peripheral margin and to biopsy base. Histological evaluation found a dermal predominant adnexal neoplasm with features of both poroma and hidradenoma. The tumor did not display significant nuclear pleomorphism, significantly elevated mitotic rate or infiltrative growth pattern (Fig. 3 and 4). Although the histological features suggested a nonmalignant PH, the patient’s age, the potential for tumor heterogeneity within adnexal neoplasia, and positive margins of the biopsy, conservative re-excision was recommended. Surgical excision was then performed with 1 cm margins for a total excision area of 3.9 × 1.7 × 1.0 cm. Residual lesion contained PH with negative margins. Within the wide excision specimen, there were some atypical features including focally increased mitotic rate, and scant necrosis but not fulfilling criteria for malignancy. Overall, the lesion remained well-defined and symmetrical without infiltrative borders.

A systematic review of the literature was performed to identify all published reports of PH. PubMed and Google Scholar databases were used to identify papers. The search term “poroid hidradenoma” in PubMed yielded in 41 results. Papers were limited to the English language. Titles and abstracts screened to identify papers with confirmed PH diagnoses based on histology. Seven papers were excluded based on titles or abstracts not related to true PH cases (such as other poroma subtypes, hidradenomas of apocrine differentiation, or malignant sweat gland tumors). To ensure all published cases of PH, they were captured in this systematic review, all cited articles (within the 34 articles identified) were also located if not a result of the original search. Articles were further analyzed for the following parameters: patient age, patient sex, location of lesion, duration of lesion, associated symptoms, gross appearance of lesion, diagnostic workup results, differentials stated, treatment, and recurrence of lesion. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000531052).

A total of 32 articles and 74 cases were identified that met the inclusion criteria plus the 1 patient described here (see Table 1). We found that PH affected a wide range of ages (13–81 years) with a mean age of 57 years. The male:female ratio was 1.28:1. PH has also been found at a variety of locations, involving the hands, feet, limbs, trunk, head/neck including face and scalp, back, chest/breasts, abdomen, buttock, and vulva. Signs and symptoms of PH were also broad, but often presented as a slow-growing, painless subcutaneous mass, sometimes with overlying normal pink skin but frequently associated with a dark and/or bluish discoloration. The cystic components of PH can impart a blue hue to the tumors, a characteristic known as Tyndall phenomenon [11, 12, 37]. Treatment was generally excision, and recurrence was found to be uncommon.

PH is one of the four variants of poroid neoplasms characterized by a single or multilobulated nodule contained within the dermis with no connection to the overlying epidermis [27, 38]. These tumors are composed of two types of cells: small, round, basophilic poroid cells and eosinophilic, squamoid cuticular cells with eccrine differentiation [6]. PH is thought to be a benign cutaneous neoplasia with low (<1%) risk of malignant transformation [32]. However, complete surgical excision remains the standard treatment due to possible advancement of pathology from a benign eccrine poroma to eccrine porocarcinoma [39‒41] or development of carcinomatous changes to hidradenocarcinoma [42], as well as to prevent recurrence, and due to its common misdiagnosis for malignant subcutaneous neoplasms.

In fact, although, generally benign most eccrine sweat gland tumors of all types are excised due to misdiagnosis, patient complaints, or malignant potential. These poroid neoplasms may be clinically difficult to differentiate from other cutaneous lesions, as well as from each other, without histological examination. Eccrine poroma, hidroacanthoma simplex, dermal duct tumor, and PH share a common cellular composition of poroid and cuticular cells and have been suggested to exist more on a spectrum of poroid neoplasms with eccrine differentiation rather than as independent entities [6, 43]. In their pioneer article, Abenza and Ackerman defined PH as a fourth additional variant of the poroid neoplasms and defined each subtype according to location of the neoplastic cells and their architecture. Lesions were termed hidroacanthoma simplex when the neoplastic poroid cells were confined entirely within the epidermis and are arranged in ovoid nests. Tumors were given the designation eccrine poroma when the cells involved basal layer of the epidermis and extended into the superficial part of the dermis. Neoplasms were named dermal duct tumor when neoplastic poroid cells were restricted to the dermis and formed of discrete nodules, widely spaced and devoid of cysts. Lastly, when the neoplastic poroid cells are in a tumor with solid and cystic components, contained within the dermis without connection to the epidermis, the neoplasm is called PH. Among the group of eccrine adnexal tumors, PH is thought to be the rarest type [6, 36, 20].

While PH is repeatedly quoted to be a rare diagnosis with very few reported cases, our systematic review reveals the incidence of PH may be underestimated. Here, we have presented the most comprehensive systematic review of reported PH to date (as of January 2022). While <100 cases of PH have been reported since its initial recognition in 1990, the close relationship between poroid neoplasms may complicate recording its true incidence. We have found multiple reports of composite tumors, including PH mixed with eccrine poroma [12, 44], hidrocanthoma simplex [12], and dermal duct tumor [11]. Additionally, we have shown that PH presents with high variability in both characteristics of the presenting lesion and patient population. The slow-growing and often painless nature of PH may lead to patient delay in presentation until size or color change raises concern, or not at all. All of these factors may be leading to underdiagnosis and PH may be more prevalent than previously thought.

Ethical approval is not required for this study in accordance with local or national guidelines. Written informed consent was obtained from the patient for publication of the details of their medical case and any accompanying images.

The authors have no conflicts of interest to declare.

No funding source for this study.

Arrin Brooks: completed the review of the literature and primary author of the manuscript. Mariah Morris: obtained histological data and edited manuscript. Jonathan Cuda: analyzed histological samples and wrote histological descriptions. Armein Rahimpour: edited manuscript. Semeret Munie: performed lesion excision and oversaw the study.

All data generated or analyzed during this study are included in this article and its online supplementary material files. Further inquiries can be directed to the corresponding or senior author.