Solitary syringoma. Report of five cases and clinicopathologic comparison with microcystic adnexal carcinoma of the skin.

Five cases of solitary syringoma (SS) were found by the authors in a search of adnexal neoplasms seen over an 18-year period. These tumors all occurred in adults as mobile, flesh-colored, circumscribed papules of the facial skin, measuring < or = 5 mm in greatest dimension. Each was cured by simple punch or shave biopsy excision. Comparison with nine histologically similar variants of microcystic adnexal carcinoma (MAC) showed that the latter lesions differed from SS in that they showed much deeper invasion, with regular involvement of the underlying subcutis and perineural or vascular-adventitial infiltration. Moreover, SS was wider than it was deep on microscopic examination, whereas the converse pertained to MAC. Knowledge of the typical clinicopathologic attributes of these two tumor types should prevent clinicians and pathologists from confusing them with each other.