Inter-Observer Variation in Ultrasound Measurement of the Volume and Diameter of Thyroid Nodules

ABSTRACT

OBJECTIVE: Thyroid nodule measurement using ultrasonography (US) is widely performed in various clinical scenarios. The purpose of this study was to evaluate inter-observer variation in US measurement of the volume and maximum diameter of thyroid nodules. MATERIALS AND METHODS: This retrospective study included 73 consecutive patients with 85 well-defined thyroid nodules greater than 1 cm in their maximum diameter. US examinations were independently performed by using standardized measurement methods, conducted by two clinically experienced thyroid radiologists. The maximum nodule diameter and nodule volume, calculated from nodule diameters using the ellipsoid formula, were obtained by each reader. Inter-observer variations in volume and maximum diameter were determined using 95% Bland-Altman limits of agreement. The degree of inter-observer variations in volumes and the maximum diameters were compared using the Student's t test, between nodules or = 2 cm. RESULTS: The mean inter-observer difference in measuring the nodule volume was -1.6%, in terms of percentage of the nodule volume, and the 95% limit of agreement was +/- 13.1%. For maximum nodule diameter, the mean inter-observer difference was -0.6%, in terms of percentage of the nodule diameter, and the 95% limit of agreement was +/- 7.3%. Inter-observer variation in volume was greater in nodules of 1 cm should not be considered as a real change in size.