Atypical Clear Cell Hidradenoma: Case report and a brief review of the literature

Clear cell hidradenoma (CCH) is an uncommon adnexal neoplasm that usually behaves in a benign fashion. However, it may present diagnostic and therapeutic challenge when atypical histologic features and persistent clinical progression are present. We report the case of a 39-year-old woman with a slowly enlarging left shoulder lesion that had initially been diagnosed on superficial shave biopsy as benign eccrine poroma. Despite this benign interpretation, the tumor enlarged over 18 months, developed violaceous discoloration, and bled intermittently after minor trauma. Magnetic resonance imaging (MRI) demonstrated a well-circumscribed, enhancing, solid-cystic dermal and superficial subcutaneous mass. Wide local excision revealed a clear cell hidradenoma with atypical features, including solid and cystic architecture, clear glycogen-rich cells, poroid cells, focal necrosis, scattered mitotic activity, subcutaneous extension, and positive deep and peripheral margins. Immunohistochemistry (IHC) supported adnexal differentiation, and molecular testing was negative for MAML2 rearrangement. 
This case illustrates the limitations of superficial sampling, the importance of correlating pathology with continued clinical change, and the need for complete excision and close surveillance when hidradenoma demonstrates worrisome but not frankly malignant features. It also reinforces the value of multidisciplinary review in guiding definitive management.