Fine Needle Aspiration of Pleomorphic Adenoma and Adenoid Cystic Carcinoma of Salivary Gland Origin

OBJECTIVE: To determine the cytologic similarities, distinctive features and diagnostic problems on fine needle aspiration in patients with pleomorphic adenoma (PA) and adenoid cystic carcinoma (ACC) of salivary gland origin. STUDY DESIGN: We reviewed the preoperative cytology and histologic sections in 22 patients in whom the resected specimens were diagnosed as PA (17 cases) or ACC (5 cases) of salivary gland. RESULTS: Concordant results were noted between cytologic and histologic diagnoses in 20 cases (91%) and discordant results in 2 cases (9%). Both discordant aspirates had been diagnosed as PA; however, their resected specimens were diagnostic of ACC. Although there were cytologic features common to both tumors, each had a unique relationship of epithelial cells to stroma. Aspirates in PA showed cell clusters with a "sunburst" appearance caused by peripheral spindled cells streaming into a fibrillar myxoid stroma. In ACC well-delineated, tightly cohesive, basaloid cells surrounded mucoid/hyaline globules or clear spaces in a honeycomb pattern. CONCLUSION: The cytologic distinction between PA and ACC in most cases was easily made on adequately cellular aspirates. In the two aspirates with discordant results, diagnostic difficulty resulted when the distinctive relationship between epithelial cells and extracellular matrix was not recognized in sparsely cellular specimens, in part due to lack of observer familiarity with the different patterns.