[Comparison of the usefulness of intraoperative examination and fine needle aspiration biopsy in thyroid lesions. Analysis of discordant cases in aspiration biopsy].

INTRODUCTION: Fine-needle aspiration biopsy (FNAB) is currently considered the most reliable and cost effective examination for diagnosis of solitary thyroid nodules prior to surgery. Because of its great utility the indication of intraoperative examination (IOE) (macroscopic examination, cytology and frozen section), has recently been questioned.

OBJECTIVE: To compare the accuracy of the FNAB and IOE, in those patients with nodular thyroid disease who undergo thyroidectomy. As well as to analyse the, discrepant cases by FNAB.

MATERIAL AND METHODS: The results of IOE and FNAB were compared in a period of two years (1997-98) at the Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán (INCMNSZ). In all cases the diagnosis established from paraffin embedded tissue sections was considered to be the gold standard. The cytologyc smears and the histologic sections of the discrepant cases were reviewed.

RESULTS: One thousand and fourteen IOE were done during two consecutive years; from these cases, 136 (13.4%) were thyroid lesions. Half of the thyroid lesions (69 cases) corresponded to carcinomas, the others were follicular adenomas (13 cases) and non-neoplasic lesions (54 cases). The analysis of the copacity to discriminate between malignant and benign diseases with IOE and FNAB demonstrated sensitivity of 89% (CI: 78.2-95.1) and 97.7% (CI: 86.8-99.9), specificity of 100% (CI: 93.1-100) and 90% (CI: 90.4-96.7). The positive predictive value of 100% and 91.6%, negative predictive value of 90.4% and 97.3%, and equal accuracy (94.6% and 94.1% respectively). When the analysis of capacity to stratify diseases was performed, IOE and FNAB showed similar percentages in all the cases, including the follicular adenomas and carcinomas. The causes of false positive and false negative cases by FNAB, reproduce what has been written in the literature.

CONCLUSIONS: FNAB preoperative examination is adequate for the selection of patients that undergo thyroidectomy. Nevertheless, IOE should be done in most of the cases, and routinely in those cases with inconclusive FNAB results and in cases of follicular tumor.