Basal cell (monomorphic) and minimally pleomorphic adenomas of the salivary glands. Distinction from the solid (anaplastic) type of adenoid cystic carcinoma in fine-needle aspiration.

Cytologic features of the cell-stroma interface are useful in distinguishing between monomorphic adenomas of the basal cell type and adenoid cystic carcinoma. In basal cell adenomas, the collagenous stroma interdigitates with adjacent cells, whereas in adenoid cystic carcinoma, the two are separated by a sharp smooth border. Furthermore, the stroma of basal cell adenomas can contain rare spindle cells or capillaries, but the cylinders of adenoid cystic carcinoma are acellular. The authors review their experience with five cases of basal cell adenoma, and three cases that were designated "minimally pleomorphic adenomas." The latter group showed the small blue cell pattern of basal cell adenoma at the time of fine-needle aspiration, and histology revealed only small foci of typical pleomorphic adenoma. With the exception of one cystic case, the cell-stroma interface of basal cell adenoma was observed in all eight cases. These cases are contrasted with three adenoid cystic carcinomas with extensive solid (anaplastic) areas. All showed the small blue cell pattern and cell-stroma interface features of basal cell adenoma. Neither showed the smooth-bordered cylinders of adenoid cystic carcinoma. Two of these three were incorrectly interpreted as benign at the time of fine-needle aspiration. The authors suggest that the stroma aspirated from solid adenoid cystic carcinoma represents desmoplastic tumor stroma that mimics the pattern of basal cell adenoma in smear material. Distinction between basal cell adenoma and the solid type of adenoid cystic carcinoma at the time of fine-needle aspiration remains a very difficult problem.