Poroid hidradenomas – a case series

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Introduction: Poroid hidradenomas (PH) are rare benign skin adnexal tumours with eccrine differentiation. PH have features of both poroma and hidradenoma, and are wholly intradermal. Few PH have been reported in the literature, and here we present two cases of PH localised to the left knee. The common histological examination finding was a circumscribed cyst lined by basaloid cells resembling poroma, with occasional ductal structures. Case reports: Patient 1 is a 27-year-old male who underwent resection of a cyst on the left knee. A fragment of tan tissue was received. Microscopic examination showed a cyst surrounded by fibrous stroma, with no solid component. There was evidence of rupture with granulomatous inflammation and cholesterol clefts. The cyst lining showed basaloid to squamoid cells resembling poroma, with occasional ductal structures. The case was signed out as a poroid hidradenoma. Patient 2 is a 63-year-old male who underwent resection of a cyst on the left knee. A 5 mm cyst was evident macroscopically. Microscopic examination demonstrated a cystic lesion lined by choroid and cuticular type cells. There were duct like structures within the cyst wall, and the cyst contained eosinophilic material. The case was signed out as a cystic poroid hidradenoma.