Accuracy of fine-needle aspiration biopsy of the thyroid combined with an evaluation of clinical and radiologic factors

Fine-needle aspiration biopsy (FNAB) of thyroid nodules is an operator-inte rpreter-dependent procedure whose diagnostic accuracy has deficiencies, esp ecially concerning indeterminate and negative results. There are reports in the literature of up to a 15% definitive diagnosis of carcinoma in the fir st category of cytology and an 11% false-negative rate in the second catego ry. With these facts in mind, a prospective study was done at the Institute Nacional de Cancerologia, Mexico City, to determine whether one or several clinicoradiologic factors were associated with a final pathologic diagnosi s of carcinoma, thereby increasing the diagnostic accuracy of thyroid FNAB. In total, 200 cases were reviewed, and 159 patients underwent surgery. Our study group comprises these 159 patients. The only clinical factor associa ted with false-negative results was size greater than or equal to 4 cm, wit h no statistical significance for the other factors analyzed. A comparison was done between clinical factors of patients who had indeterminate results in the aspirate and those of patients who had a definitive diagnosis by pe rmanent section of the thyroid carcinoma, where an association was found be tween malignancy and tumor size greater than or equal to 4 cm, irregular bo rders, fixed lesions, and heterogeneity on ultrasound. We conclude that in the presence of a negative cytology result, with tumor size greater than or equal to 4 cm, close follow-up is indicated, and a new thyroid FNAB should be performed in 6 months. If the nodule persists or grows, a surgical proc edure should be considered. In the case of an indeterminate cytology result and in the absence of those factors associated more frequently with a path ologic result of carcinoma, a conservative approach could be indicated with clinical followup and repeat thyroid FNAB in 6 months to 1 year.