Adult-onset linear syringocystadenoma papilliferum over the inguinal fold: a case report with emphasis on mast cell staining pattern.

Syringocystadenoma papilliferum (SCAP) is a rare hamartoma with predominant apocrine differentiation. Clinically, presenting as solitary nodule, nodular plaque, or linear nodules, SCAP usually occurs over the head and neck region in children. Out of these three morphological presentations, the linear type is the most rare. We report herein a case of a 36-year-old man with linear SCAP over the right inguinal fold, for its rarity. Besides the typical histologic features, a marked increase in lesional mast cell concentration as compared to a control specimen obtained from an unaffected site and a strikingly raised number of spreading and degranulated mast cells were demonstrated.