A Comparison of the Diagnostic Efficiency of Guided Fine Needle Aspiration Cytology Versus Conventional Fine Needle Aspiration Cytology of the Thyroid

Fine needle aspiration cytology (FNAC) is possibly the most useful investigation for the thyroid. However, conventional FNAC (C-FNAC) is limited by a high rate of inadequate samples. Ultrasound guided FNAC (US-FNAC) has been proposed as an alternative. This study aims to estimate the measures of diagnostic accuracy of FNAC as well as to compare US-FNAC against C-FNAC. Patients who underwent FNAC at our for a period of 5 years were selected. This comprised of 237 C-FNAC cases and 173 US-FNAC cases. Out of these 410 cases, 129 cases had cyto-histological correlation. The proportion of inadequate samples, malignant cases as well as indeterminate cases were compared between US-FNAC and C-FNAC. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratios for positive and negative results and odds ratio were estimated for overall FNAC as well as US-FNAC and C-FNAC patients. US-FNAC has a significantly lower proportion of inadequate samples (0.58 vs. 15.19%), as well as a lower proportion of indeterminate samples (1.7 vs. 7.6%) and a higher proportion of malignant cases (6.4 vs. 2.1%). When the inadequate samples were excluded, the results for tests of diagnostic effectiveness for overall FNAC, US-FNAC and C-FNAC respectively ranged between 66.67 and 80% for sensitivity, between 86.05 and 100% for specificity, between 45.45 and 100% for PPV and between 97.37 and 98.7% for NPV. FNAC is a useful test for differentiating malignant from benign lesions. When inadequate samples are excluded, both US-FNAC and C-FNAC are accurate diagnostic tests. However, US-FNAC is a more useful test since it results in a lower number of inadequate samples. Also, US-FNAC results in a greater yield of malignancy and a lower percentage of indeterminates, possibly due to additional information received from ultrasound examination.