The WHO classification of salivary gland tumours distinguishes three types of monomorphic adenomas (cystadenolymphoma, onkocytoma and 'other types'). In the material of the salivary gland register (1965-1978), 362 monomorphic adenomas were investigated (252 cystadenolymphomas, 5 onkocytomas and 105 cases of 'other types'). In the tumour group of 'other types' the 'salivary duct adenoma' represented the most frequent type (79 of 105 cases=75%). The following determinations were made for the definition and differential diagnosis of the salivary duct adenoma: 1. The salivary duct adenoma was localized predominantly in the parotid gland (57 cases=72%), in the other cases (22 cases=28%) in the minor salivary glands (especially upper lip, cheek and palate). The age peak is in the seventh decade, the female sex predominates with 65%. 2. In the histologic architecture trabecular, tubular and cystic duct formations can be distinguished which are limited by a PAS-positive basement membranelike substance at the outside. There is no mucoid or chondroid stroma such as is found in pleomorphic adenomas. 3. The cytologic structure is characterized by basal reserve cells (basal cells) at the outside and by variably differentiated duct epithelias at the inner side with secret production into the duct lumen. Within the trabecular lumenless formations so-called transformation cells are found. 4. The histologic and cytologic differentiation is comparable with the embryonal stages of the salivary duct system as well as with mature parts of salivary ducts. Tubular and cystic structures represent higher stages of maturation and are found more frequently than trabecular formations which correspond to the early stages of the salivary duct's embryogenesis. 5. The term 'salivary duct adenoma' comprises all monomorphic adenomas with ductlike structures and replaces the many synonyms previously used ('trabecular, tubular, canalicular adenomas; cystadenomas'). Rare types of adenoma which were especially described in the minor salivary glands ('papillary cystadenoma; sialadenoma papilliferum, intraductal papilloma') are also included under the term 'salivary duct adenoma'. 6. The basal cell adenoma is subclassified as a special variant of the salivary duct adenoma. The term 'basal cell adenoma' is only used for adenomas which possess the characteristic structure of basal cells and have a distinctly limited stroma. We found 19 basal cell adenomas (=18%) in the group of monomorphic adenomas of 'other types'. 7. In differential diagnosis, the salivary duct adenoma must be distinguished from the stroma-poor pleomorphic adenoma and from other rare monomorphic adenomas (sebaceous lymphadenoma, clear-cell adenoma, mucous-producing adenoma, etc.). © 1979 Springer-Verlag.
