Ductal adenomas of salivary gland showing features of striated duct differentiation ('striated duct adenoma'): a report of six cases

Aims: To describe a salivary adenoma composed largely of unilayered ducts resembling striated ducts, and to differentiate it from similar adenomas, including canalicular and intercalated duct adenoma. Methods and results: Six unilayered ductal adenomas were identified in parotid (four) and palate (two). They were encapsulated, ranged from 0.5 to 3.0 cm and composed of closely apposed ducts with virtually no stroma. The ducts varied in size and showed cysts up to 0.1 cm. The cells were eosinophilic and bland. Prominent cell membranes, reminiscent of 'striations' of normal striated ducts, were seen. The typical epithelial 'beading' pattern with abundant stroma of canalicular adenoma was absent. The tumours expressed keratins (six of six) and S100 (five of six). Smooth muscle actin (SMA) revealed no myoepithelial cells. Two tumours showed focal bilayered ducts with calponin or smooth muscle myosin heavy chain, but the tumours were largely unilayered. Only isolated cells in three tumours were positive with p63; a pattern identical to striated ducts. In contrast, the normal excretory and intercalated ducts all contained diffuse bilayering with basal or myoepithelial markers. Conclusions: Striated duct adenomas are unilayered ductal tumours that recapitulate normal striated ducts.