Purpose: To evaluate measurements of thyroid volume by two different US methods and CT in a blinded design.
Material and methods: Four observers evaluated 27 patients. Observer 1 used US and calculated thyroid volume based on recordings of cross-sections through the gland. Observer 2 used US and calculated the volume of each lobe as a rotation ellipsoid. Observers A and B used CT images and calculated thyroid volume based on recordings of cross-sections through the gland. All measurements were made twice.
Results: The median thyroid volume was 81 ml (range 7-470 ml) evaluated by CT. All three methods had fair reproducibility. When correlating the two different methods using US, an r of 0.837 was found. When correlating data from patients without intrathoracic goitre evaluated by US (Observer 1) and CT, r = 0.945. The method based on a rotation ellipsoid systematically produced smaller thyroid volumes than those of the cross-sectional method. Evaluation by US systematically produced smaller thyroid volumes than CT.
Conclusion: Calculation of thyroid volume based on US recordings of cross-sectional areas is a reproducible method in patients without substernal goitre extension. The US method calculating thyroid volume as a rotation ellipsoid is less reproducible, especially in large goitres. Measurement of thyroid volume using CT should be preferred in goitres with substernal extension.