Evaluation the Relationship Between Thyroid Nodule Size with Malignancy and Accuracy of Fine Needle Aspiration Biopsy (FNAB)

INTRODUCTION: Some studies have shown largest thyroid nodule size, especially ≥4cm that can predict malignancy and reduce fine needle aspiration biopsy (FNAB) accuracy. Therefore, this study is designed to evaluate relationship between thyroid nodule sizes with malignancy and its effect on FNBA accuracy. MATERIALS AND METHODS: a retrospective analytical study design aims to investigate all patients with thyroid nodules who referred to surgery department of Imam-Khomeini Hospital of Mazandaran University of Medical Sciences in Sari from 20 March 2008 to 22 March 2014. We collected patient’s demographic data, nodules size, FNAB reports and final pathology (after surgery) reports from their medical records. All data were analyses performed by SPSS18. RESULTS: 167 patients (153 women) with mean age of 41.56±13.24 years old were enrolled for this study. In final pathology; 38 patients (22.8%) had malignant nodules. The mean age of patients with or without malignant nodules were 34.93±11.86 and 42.37±12.26 years old, respectively (P=0.002). The mean size of benign and malignant nodules were 2.91±1.29 cm and 3.38±1.86 cm, respectively (P=0.15). 25.2% of <4 cm nodules and 17.9% of ≥4 cm nodules were diagnosed as a malignant (P=0.29). FNAB was done on 95 patients that reported benign in 60 patients (63.2%), malignant in 18 patients (18.9%) and suspicious in 17 patients (17.9%). Positive and negative results of FNAB in all nodules were 3.5% and 6.3%, in <4cm nodules were 5.8% and 6.2% and in ≥4cm nodules were zero and 6.7%, respectively. The sensitivity, specificity, Positive predict value (PPV), negative predict value (NPV) and overall accuracy (OA) of FNAB in all nodules were 76.19%, 96.49%, 88.88%, 91.66% and 91.02%, and in <4cm nodules were 78.57%, 94.11%, 84.61%, 91.42% and 89.58%, and in ≥4cm nodules were 71.4%, 100%, 100%, 92% and 93.33%, respectively. CONCLUSION: the results of this study revealed that the size of the thyroid nodules is not reliable at predicting malignancy and should not be applied in medical decision making. FNAB showed good specificity but the sensitivity was low in our study. In ≥4cm nodules; FNAB sensitivity was decreased and accompanied by higher false-negative results. Furthermore, FNABs with suspicious results were associated with high probability of malignancy.