The Diagnosis: Nodular Hidradenoma
Nodular hidradenomas (NHs) are rare benign cutaneous adnexal neoplasms first described in 1949 as clear cell papillary carcinomas.1 Since then, various terms have been used to describe this entity, such as eccrine acrospiroma, solid-cystic hidradenoma, and clear cell hidradenoma.2 Review of the literature revealed a female predominance (2:1 ratio) and a mean age at presentation of 37.2 years.3,4 Nodular hidradenoma presents as an asymptomatic, solitary, mobile, firm nodule with intact overlying skin. Rarely, multiple nodules may occur.3 Some tumors display ulceration and serous fluid leakage.5 They occur most commonly on the scalp, face, and upper extremities with an average size of 2 cm.3 Rapid growth of the tumor may signal a malignant change.6
Histopathology reveals a lobulated, circumscribed, symmetrical tumor with dermal nests of epithelial cells that are polygonal with eosinophilic cytoplasm forming ductlike spaces (Figure). However, clear cell changes and squamous differentiation may be prominent features. Cystic spaces may result from tumor cell degeneration. Most tumors are encased by collagenous fibrous tissue and rarely have epidermal attachments.3
  Anastomosing aggregates of squamous cells forming ductlike spaces were viewed on low-power magnification (A)(H&E, original magnification ×10). On higher power there were ductlike spaces and eosinophilic hyalinized stroma entrapped by the bland-appearing squamous proliferation (B)(H&E, original magnification ×20). |
Nodular hidradenoma traditionally has been considered to be of eccrine origin, but more recent literature indicates that the majority of NHs are of apocrine origin. Histologically, apocrine tumors display eosinophilic secretion, mucinous epithelium, squamous or sebaceous differentiation, and decapitation secretion, whereas eccrine tumors are identified by their lack of specific features.3
Nodular hidradenoma may recur after excision. Malignant transformation is rare. In one review, 6.7% (6/89) of NHs were malignant, characterized by abnormal mitoses, nuclear atypia, and necrosis.4 Malignant NH or nodular hidradenocarcinoma behaves aggressively with up to an 86% local recurrence and 60% rate of metastasis within 2 years.6 Survival time is inversely proportional to the size of the tumor and is generally poor, with a 5-year disease-free survival of less than 30%.6,7
Treatment of NH is achieved through primary excision or Mohs micrographic surgery; however, treatment of nodular hidradenocarcinoma is controversial and typically begins with wide local excision but may involve lymph node dissection if necessary. Use of adjuvant chemotherapy and radiation therapy for metastases warrants more clinical studies, as it is a rare occurrence.6 Our patient planned to undergo a total excision of the benign nodule once she healed from the biopsy; however, she was lost to follow-up, as she moved out of state.