Causes of false results in transthoracic fine needle lung aspirates.

To evaluate the causes of false-negative and false-positive results in transthoracic fine needle aspirates (TFNAs), we reviewed our experience with this technique over the 20-year period from 1972 to 1991. For 488 TFNAs satisfactory for cytologic interpretation, tissue diagnoses were subsequently obtained by biopsy, resection or autopsy in 218 cases (56 benign and 162 malignant). In 11 cases, TFNA was positive for malignancy, and the biopsy was negative. Review of these cases disclosed that the TFNAs were true positives (specificity, 100%) and that the biopsies failed to sample the lesion. There were 18 false-negative results by TFNA, for a sensitivity of 90%, all as a result of failure to sample the lesion. TFNA is a highly specific and sensitive technique for diagnosis of benign and malignant lung masses. False negatives are the result of failure to sample the lesion. False positives are uncommon but can be avoided if the cytopathologist is aware that benign reactive lesions may mimic malignancy on cytology.