SONOGRAPHIC STUDY OF THE THYMUS IN INFANTS AND CHILDREN

Because of variability in the size of the thymus, imaging in children is a challenge. Difficulties ill differentiating an abnormal mediastin al mass from a normal thymus may lead to unnecessary investigations. W e performed a prospective sonographic study of the normal thymus in 14 0 infants and children aged newborn to 8 years to determine the size o f the normal thymic gland. Patients were classified into five groups b y age: 1) less than 6 months. 2) 6-12 months, 3) 13-24 months, 4) 25-4 8 months, 5) more than 48 months. The thymus was scanned through the s uprasternal, transsternal. and parasternal windows with a Sonos 1000 s canner and a 5.5-MHz sector probe. The thymus was visualized in at lea st one of thee three windows and the width and thickness were measured in 133 of the 140 cases. The mean +/- standard deviation width and th ickness were 3.67 +/- 0.64 cm and 130 +/- 0.25 cm in boys and 3.45 +/- 0.59 cm and 1.20 +/- 0.26 cm in girls (p = 0.047 and p = 0.033 in wid th and thickness , respectively). Regression analysis demonstrated an increase, mainly in the width. with increasing age (width = 3.48 + (0. 05 x age) cm, p = 0.009), indicating on increase of 0.05 cm per year. In conclusion, tile thymus was clearly and easily visualized on sonogr ams in the majority of children we studied. This study established the normal size range of tile thymus in children less than 8 years old.