Basal-cell adenoma of parotid. Difficulty of differentiation from adenoid cystic carcinoma on aspiration biopsy

Two cases of basal-cell adenoma (basaloid monomorphic adenoma, dermal analogue tumor) seen in a one-year period were subjected to fine needle aspiration biopsy and subsequent histologic confirmation. Two cases of adenoid cystic carcinoma occurring in the parotid region were selected for comparison; a great similarity between the two types of tumors was noted. On aspiration smear both lesions consisted of clusters and sheets of uniform, small, regular cells with scant basophilic cytoplasm and regular round or oval bland nuclei. The smears contained varying amounts of homogeneous, pale, eosinophilic stromal substance within and around the cell clusters. Individual cell differences between the two lesions were minimal, with the adenoid cystic carcinomas tending to exhibit more nuclear hyperchromatism and irregularity; the architectural arrangements of the cell clusters and the stromal substance permitted differentiation between the two lesions.