Assessment of the thymic morphometry using ultrasound in full-term newborns

The size of thymus is variable and depends on age of the individual. Thymus undergoes its maximum development at the time of birth, when it also has the greatest relative weight. The aim of our study was to compare the two ways of expressing the size of the newborns' thymus, the Thymus index and estimated volume of thymus.

The examined group consisted of 212 full-term newborns from Slovakia, Europe. We estimated the length, width and thickness of the left and right lobes. We used these data to calculate the approximate volume of the thymus. We also expressed size of the thymus as a multiple of the transverse diameter of the cranial part of the thymus and the sagittal area of the larger lobe of the thymus, the so-called Thymus index. Bilateral differences in thymus lobes' sizes, as well as the thymus' sizes between sexes and among the newborns of different types of birth were also analysed.

Our results show that (1) the left thymus lobe is longer and thicker than the right lobe; (2) the Thymus index and the estimated volume of the thymus have a strong significant and positive correlation; (3) boys reach significantly higher values of the Thymus index than girls; and (4) when comparing the differences in the thymus size between the newborns born in two different ways (spontaneous and operatively), no significant difference was discovered.

Ultrasound examination is safe, effective and suitable for simple assessment of the thymus size, which has a great variability in children. In other hand, the use of the Thymus index in everyday clinical practice is limited due to different mean values in a number of studies.