Hidradenoma
Key Points
Most hidradenomas are probably of apocrine rather than eccrine origin
Fifty percent of hidradenomas harbor the t(11;19) translocation: the fusion of MECT1 gene on chromosome 19p13, with the MAML2 genes on chromosome 11q21
Definitive treatment is via complete excision with clear margins
Hidradenomas are generally benign lesions
Recurrences are possible if the lesion is incompletely excised
The malignant potential is rare or negligible
The malignant variety is called hidradenocarcinoma and may occur de novo, or less commonly on top of a benign hidradenoma
The human skin contains several million sweat glands (also termed “sudoriferous glands”), which are small tubular structures in the skin that are concerned with the production of sweat, and of which there are two types, the water-producing eccrine sweat glands, which express their secretion by exocytosis (merocrine secretion), and the oil-producing apocrine sweat glands, which express their secretions by a process of apical decapitation of the secretory cells.1,2,3,4,5,6,7,8,9,10 The glandular portion of both types is located in the dermis. The eyelid apocrine-pilosebaceous glands (also termed apocrine glands of Moll) are only observed at the eyelid margin, and they open into the infundibulum of the pilosebaceous unit (the hair follicles) leading to the surface of the skin.1,4,5,9,10 However, eccrine sweat glands are not associated with hair follicles, and they open directly onto the epidermal surface via a long straight ductule, which has an apical intraepidermal portion (the acrosyringium).10 Eccrine sweat glands are located in the pretarsal and preseptal regions but not in the eyelid margin. Although the human skin contains far more eccrine sweat glands than their apocrine counterpart, the eyelid is one of the few regions in the body where apocrine sweat glands (glands of Moll) are abundant. Both glands could be a source of origin of several sweat gland cystic swellings and neoplasms that are mostly benign but may rarely be malignant.1,2,3,4,5,6,7,8,9
Hidradenomas are relatively rare benign adnexal neoplasms arising from the tubular secretory epithelium of the sweat glands, but they are of uncertain eccrine or apocrine derivation.1,2,3,4,5,6,7,8,9 The condition is alternatively known in the literature as eccrine hidradenoma, apocrine hidradenoma, clear cell hidradenoma, nodular hidradenoma, eccrine acrospiroma, solid-cystic hidradenoma, or nodulocystic hidradenoma.3,4,8,11 This nomenclatorial complexity, besides its uncertain origin (eccrine vs apocrine vs both), has led to significant confusion in the literature when dealing with the condition and probably reflects the different approaches between pathologists in interpreting the histologic features of the disease.3
Etiology and Pathogenesis
The cellular origin of hidradenoma is controversial. The understanding of this rare neoplasm and its ultrastructural features has evolved over the years from the more traditional outlook in older textbooks, which considered these neoplasms to be of an exclusive eccrine origin. Currently, the consensus is to separate adnexal neoplasms of glandular or ductal origin into eccrine or apocrine hidradenomas, even though it is sometimes impossible to identify whether a lesion is displaying eccrine or apocrine differentiation.8,11 Although it is currently accepted that hidradenomas can show either an eccrine or apocrine architecture, the apocrine characteristics are the predominant histological subtype that is demonstrable in the majority of lesions.4,5,8,11,12 This is particularly true in the periocular region where it has been demonstrated recently that apocrine tumors are far more common than their eccrine counterparts, a histological subtype that may turn out to be extremely rare in the eyelids.4,5
The common denominators of apocrine glandular differentiation are the presence of decapitation secretions and intracytoplasmic zymogen granules. However, the identification of glandular components in follicular or sebaceous neoplasms, even in the absence of either defining feature (decapitation or zymogen granules), almost certainly represents apocrine differentiation. This premise is supported by embryologic evidence because the apocrine glands, hair follicles, and sebaceous glands have a shared origin from pluripotential germinative cells present in the follicles. All three structures are histologically integrated as the apocrine-pilosebaceous unit.3,8,11,13 However, there is no single microscopic finding that is ultimately specific for eccrine glandular differentiation. When the hallmarks of apocrine disease are absent (decapitation secretion, intracytoplasmic zymogen granules, or accompanying follicular or sebaceous differentiation), an eccrine origin may be suspected but the lack of
these findings is not definitive. It may not be entirely implausible to suggest that the diagnosis of an eccrine hidradenoma may be one of exclusion.3,11 What complicates matters further is that neither enzymatic studies nor electron microscopy or even immunohistochemical studies are of much help to elucidate the subtype of hidradenoma.11 Therefore, the current consensus supports a presumed apocrine morphological predominance of hidradenomas.3,4,5,8,11
these findings is not definitive. It may not be entirely implausible to suggest that the diagnosis of an eccrine hidradenoma may be one of exclusion.3,11 What complicates matters further is that neither enzymatic studies nor electron microscopy or even immunohistochemical studies are of much help to elucidate the subtype of hidradenoma.11 Therefore, the current consensus supports a presumed apocrine morphological predominance of hidradenomas.3,4,5,8,11
The histogenesis of hidradenomas is largely unknown, and only one genetic mutation has ever been described in patients with hidradenoma.14,15 Some hidradenomas feature a t(11;19) translocation, which involves the fusion of both the mucoepidermoid carcinoma translocated 1 gene (MECT1, 19p13) and the mastermind-like 2 gene (MAML2, 11q21).11,14,15 It is estimated that about 50% of patients with hidradenoma have the CRTC1-MAML2 gene fusion, which is particularly common in the clear cell variant of hidradenomas.15 There are no other known predisposing factors, although some authors note that trauma may accelerate the rate of growth of hidradenoma.3
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