Sonography of the thymus in healthy children: frequency of visualization, size, and appearance.

OBJECTIVE

The purpose of this study was to determine the frequency of visualization, the size, and the sonographic appearance of the normal thymus on sonograms of children 2-8 years old.

SUBJECTS AND METHODS

Fifty children without symptoms referable to the thymus were scanned through the suprasternal notch and parasternal windows with a Diasonics DRF 100 scanner and a 7.5-MHz probe. The anteroposterior and longitudinal dimensions of the thymus were measured and the echogenicity of the thymus was subjectively assessed and compared with the liver and thyroid gland. No change was made in the time-gain compensation or overall gain settings.

RESULTS

The thymus was completely visualized and measured in 47 (94%) of the 50 patients. The mean anteroposterior and longitudinal measurements were 1.4 and 2.5 cm, respectively, for the right lobe and 1.4 and 2.9 cm, respectively, for the left lobe. On longitudinal sonograms, the right lobe tended to have an inverted teardrop shape whereas the left lobe was either triangular or sickle shaped. The mean absolute dimensions of the thymus changed little with age, although the number of children in each age group was small. The internal echogenicity of the thymus most closely resembled that of the liver.

CONCLUSION

The thymus is clearly and easily visualized on sonograms in the majority of children 2-8 years old, a much later age than reported previously.