Validation of ultrasonography of the thyroid gland for epidemiological purposes

Ultrasonography of the thyroid is often used in epidemiological surveys, th us thorough characterization of the interobserver variation of the differen t parameters obtained is important. Various methods have been used for meas uring thyroid volume, and different formulas have been used for calculation of thyroid volume from the measured dimensions. In this article, two princ iples of thyroid volume measurement are described in detail: the well-known method based on the three axes of each lobe and a new principle based on p lanimetry in two planes. The interobserver variation of the examination and the measuring procedure in itself were tested on 25 participants in a popu lation study. A comparison of postmortem ultrasonography of the thyroid and results of an autopsy was performed. Good correlation and agreement betwee n observers was found for thyroid volume (r = 0.98) and prevalence of thyro id nodules (kappa = 0.72), whereas echogenecity and echopattern showed litt le agreement. The correlation of thyroid volume by ultrasonography to autop sy results was satisfactory (r = 0.93), but the volume tended to be slightl y underestimated even when using the formula pi/6(= 0.52)*length*width*dept h. No major differences were found between the performance of the two princ iples of volume calculation. We conclude that when the measuring procedure is well defined, results of ultrasonography are comparable between observer s for thyroid volume and prevalence of thyroid nodules, but not for echogen ecity or echopattern. The formula of length*depth*width*pi/6 is suitable fo r thyroid volume measurement.