Value of ancillary studies in fine needle aspiration cytology of the lung

The importance of ancillary studies in surgical pathology of the lung is well documented. Less well established is the utility of these methods in fine needle aspiration (FNA) cytology of the lung. We reviewed our experience over a two-year period (1990-1991) with the use of ancillary studies in addition to routine light microscopy in FNA of the lung. Three hundred forty-five percutaneous aspirations were performed under radiologic guidance during this period. A diagnosis of malignancy was made in 233 (68%) cases. Thirty-two aspirates provided specific benign inflammatory or infectious diagnoses of mass lesions. Approximately one-half the cases required no additional studies (181/345, 52%). Immunocytochemistry was performed in 50 cases (14.5%), electron microscopy (EM) in 28 cases (8%), microbiologic staining in 42 cases (12%), mucin staining in 72 cases (21%) and cell blocks in 77 cases (22%). Immunocytochemistry and EM were generally used to classify poorly differentiated neoplasms, confirm the diagnosis of bronchioloalveolar cell carcinoma, determine neuroendocrine differentiation and establish primary sites for suspected metastatic malignancies. Immunocytochemistry provided significant additional information in 20 (40%) of the cases in which it was attempted and confirmed the light microscopic impression in an additional 18 cases (36%). Similarly, EM provided significant additional information in 10 cases (67%) and confirmed the light microscopic impression in an additional 4 cases (27%). Microbiologic staining was performed when an infectious etiology was suspected clinically or an inflammatory (especially granulomatous) background was present in the smears. In 11 cases (27%) the staining was positive for organisms. Mucin staining was performed in an attempt to better classify poorly differentiated non-small cell malignancies and was contributory in 68% of the cases. In conclusion, ancillary studies are helpful in confirming the cytologic impression and making a more specific diagnosis in FNA of the lung.