Comparison of utility of intraoperative examination and fine needle aspiration biopsy in thyroid lesions. Analysis of discrepant cases in aspiration biopsies

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 indicati on of intraoperative examination (IOE) (macroscopic examination, cytology a nd frozen section), has recently been questioned. Objective. To compare the accuracy of the FNAB and IOE, in those patients with nodular thyroid disea se who undergo thyroidectomy. As well as to analyse the, discrepant cases b y 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 Medi cas y Nutricion. Salvador Zubiran (INCMNSZ). In all cases the diagnosis est ablished from paraffin embedded tissue sections was considered to be the go ld standard. The cytologyc smears and the histologic sections of the discre pant cases were reviewed. Results. One thousand and fourteen IOE were done during two consecutive years; from these cases, 136 (13.4%) were thyroid le sions. Half of the thyroid lesions (69 cases) corresponded to carcinomas, t he 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 9 0% (CI: 90.4-96.7). The positive predictive value of 100% and 91.6%, negati ve 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 perf ormed, IOE and FNAB showed similar percentages in all the cases, including the follicular adenomas and carcinomas. The causes of false positive and fa lse negative cases by FNAB, reproduce what has been written in the literatu re. Conclusions. FNAB preoperative examination is adequate for the selectio n of patients that undergo thyroidectomy. Nevertheless, IOE should be done in most of the cases, and routinely in those cases with inconclusive FNAB r esults and in cases of follicular tumor.