[The accuracy of the fine needle aspiration biopsy in 1250 thyroid nodules]

Between 1989 and 1998 a total of 1250 thyroid nodes underwent Fine Needle Aspiration Biopsy (FNAB). Of these 150 went on to surgery with subsequent histological examination which proved positive for malignant neoplasm in 35 nodes. The remaining 115 nodes presented benign lesions. The cytological diagnoses were preventatively broken down into three groups: a) benign; b) malignant; c) suspected malignancy. Group a) included 53 nodes; histology confirmed the diagnosis of a benign lesion in 50 of these nodes (True Negatives), while 3 proved malignant (False Negatives). The cytological diagnosis of malignancy was reached in 24 nodes (group b) and subsequent histology confirmed the malignancy in 18 cases (True Positives) while the remaining 6 nodes tested negative for neoplasm (False Positives). Group c) included those thyroid nodes which cytology classified as follicular neoplasms and for which histology was required to reach a diagnosis of malignancy or benignity; for this reason these cases were not used in the evaluation of diagnostic reliability. Of these 15 (20.5%) proved malignant and 58 (79.5%) benign (44 follicular adenomas and 14 micro-macrofollicular struma nodes). On the basis of the above data, the diagnostic accuracy of FNAB is 88.3%, sensitivity 85.7% and specificity 89.3%. These findings are substantially in agreement with the international literature which considers cytological testing highly reliable. In analyzing the cases which were not confirmed by histology, it was interesting to note that among the 4 false positives--defined as the "presence of atypical cells in a lymphocyte infiltration context"--a full three were thyroadenitis nodes for which the presence of atypical cells is quite common. The three false negative nodes, on the other hand, included two cysts for which cytology did not reveal neoplastic cells. The present experience suggests the following: 1) FNAB is still the most reliable technique for the diagnosis of thyroid neoplasms; 2) the presence of atypical cells in thyroid node lesions is not always indication of a malignancy; 3) cysts must be subject to careful follow-up since they can mask a malignant neoplasm.