Objective: To audit the accuracy and impact on the frequency of operation of fine needle aspiration cytology of isolated thyroid swellings.
Design: Prospective analysis over six years of cytological predictions compared with histological findings.
Setting: Thyroid clinic serving the Grampian region.
Patients: 395 Consecutive patients presenting with an isolated thyroid swelling, 307 of whom underwent surgical excision. Analysis was confined to a subgroup of 283 patients with satisfactory aspirates who were operated on.
Results: The positive predictive value of aspiration cytology for detecting malignant disease was 100% and the sensitivity 83%. The sensitivity for the detection of neoplasia (frank malignancy together with follicular adenomas) was 76%. The specificity was 58% and the overall accuracy 69%. Recalculation of data in previous papers with strict criteria showed the accuracy of aspiration cytology to be variable and lower than is widely accepted. Since the introduction of aspiration cytology 21% fewer operations for isolated thyroid swellings have been performed.
Conclusions: As a basis of selection for surgical excision of isolated thyroid swellings according to prediction of neoplasia fine needle aspiration cytology is less reliable than is widely accepted. It is an adjunct to management rather than a definitive test, and negative cytological results do not exclude neoplastic disease. Further study should take account of the implications of repeated clinic attendances for review and aspiration as these may culminate in delayed surgical treatment.