Poroid Hidradenoma: Dermoscopic and In Vivo Reflectance Confocal Microscopic Description.

Poroid hidradenoma (PH) is a rare, benign adnexal neoplasm usually presenting as a solitary, well circumscribed, asymptomatic papule or nodule that appears reddish and is occasionally tender. Since 1990, only a few cases of PH have been reported. We present a case of PH on the medial surface of the thigh and describe, for the first time, the dermoscopic and reflectance confocal microscopic (RCM) features in correlation with histology. A 67-year-old woman with unremarkable family or past medical history presented with a nodular lesion on the medial surface of the right thigh. The lesion had appeared 4 months earlier and rapidly enlarged. Physical examination revealed a 7 × 5 mm, non-tender, reddish nodule with clinically distinct margins. Dermoscopy showed central blue-grey pigmented areas, a polymorphous vascular pattern with arborizing, glomerular and hairpin vessels surrounded by white halos. RCM revealed an ovoid, well-outlined tumor, with a central area containing cells with distinctive morphologies, two types of tumor cells, tubular hypo-reflective structures, and rectilinear vessels in the stroma. These findings correlated with histological features, which established the diagnosis of PH. Even though the diagnosis of PH remains histopathological, non-invasive tools, such as RCM, can help rule out several malignancies, therefore reducing surgical-associated comorbidity.