Monomorphic adenomas of salivary glands. Trabecular-tubular, canalicular, and basaloid variants.

Eleven cases of monomorphic adenoma of the salivary glands are interpreted as variants of pleomorphic adenomas (mixed tumors) that lack chondroid or myxomatous components. Nine of these tumors were in the parotid gland and two were on the hard palate. Monomorphic adenomas are usually encapsulated and frequently are partially cystic. Their histologic pattern may be confused with that of adenoid cystic carcinoma, but they grow in an expansile fashion and usually are monolobular. Histologically, they may be divided into trabecular-tubular, canalicular, and basaloid variants. Morphologically, they bear a resemblance to basaloid sweat-gland tumors (eccrine spiradenoma and cylindroma).