Ultrasound-guided fine-needle aspiration of thyroid nodules: does size matter?

Some authors have questioned the benefit of fine-needle aspiration (FNA) of thyroid nodules ≥ 4 cm. They report that the results of the FNA are not as reliable when compared to nodules <4 cm. The aims of this study are to evaluate the accuracy and predictive values of ultrasound-guided FNA (USFNA) of thyroid nodules ≥ 4 cm and compare these findings to nodules <4 cm.

A retrospective study of 998 patients who underwent thyroid surgery between 2006 and 2012 at the McGill University Thyroid Cancer Center was performed. USFNA and post-operative pathology diagnoses of nodules ≥ 4 cm versus those <4 cm were compared. Pre-operative USFNA results were divided into three groups: benign, indeterminate, and malignant/suspicious for malignancy subgroups. Post-operative results were separated into benign and malignant groups.

There were 225 patients with nodules ≥ 4 cm and 773 patients with nodules <4 cm. The sensitivity, specificity, positive predictive value and negative predictive value for USFNA of nodules ≥ 4 cm were 84.62% (CI 71.91-93.10), 91.49% (CI 79.6-97.58), 91.67% (CI 80.0-97.63) and 84.31% (CI 71.4-92.95), respectively. The sensitivity, specificity, positive predictive value and negative predictive value for USFNA of nodules <4 cm were 90.48% (CI 86.1-93.8), 85.92% (CI 75.6-93.02), 95.8% (CI 92.41-97.96) and 71.76% (CI 60.95-81.0), respectively. The difference in diagnostic accuracy of USFNA between both groups was not statistically significant (p>0.05).

This study shows that the sensitivity, specificity, positive predictive value and negative predictive value for USFNA of nodules ≥ 4 cm are similar to that of smaller nodules. It is therefore suggested that these nodules undergo USFNA.