MR imaging of large multinodular goiters: observer agreement on volume versus observer disagreement on dimensions of the involved trachea.

OBJECTIVE MR imaging and sonography are considered to be among the most reliable methods available for estimating goiter volume. Our aim was to assess the observer variability of MR imaging for estimating the volume of a large multinodular goiter and the dimensions of the related trachea. Additionally, we compared the goiter volume estimates from MR imaging with those from sonography. SUBJECTS AND METHODS The effect of high-dose (131)I therapy on the thyroid gland and the impact on the trachea in 23 patients with a large multinodular goiter (range in volume, 100-703 mL) were monitored by observers unaware of duplicated measurements on MR imaging (n = 68) before, 1 week after, and 1 year after (131)I therapy. In goiters exclusively cervically located (n = 12), cross-sectional planimetric sonographic measurements (n = 24) were performed simultaneously with MR imaging. RESULTS The mean intraobserver difference for the MR imaging measurements of goiter volume was 2.1 mL (1.4%, p = 0.32), and the coefficient of variation (CV) +/- SD was 3.6% +/- 2.6%. The mean interobserver difference was 0.4 mL (0.3%, p = 0.86), and the CV +/- SD was 4.1% +/- 3.5%. Compared with MR imaging, sonography underestimated goiter volume; the mean percentage difference between the volume estimates on MR imaging and those on sonography (volume estimated on MR imaging - volume estimated on sonography) was 19.5% (95% limits of agreement: -22.2% to 83.7%), and the CV +/- SD was 15.0% +/- 12.4%. The mean interobserver difference in the MR imaging measurement of tracheal volume along the goiter extension was 7.4% (95% confidence interval: 4.0-10.8%) and that of the smallest cross-sectional area of the trachea was 7.9% (95% confidence interval: 2.9-13.2%). The corresponding CV +/- SD were 8.1% +/- 6.6% and 10.3% +/- 10.3%, respectively. CONCLUSION For the estimation of goiter volume, MR imaging has low intra- and interobserver variations. In contrast, the determination of tracheal dimensions using MR imaging has a high variability and, thus, is imprecise. Sonography significantly underestimates thyroid volume compared with MR imaging in patients with a large goiter.