a. The ultrasonography image acquired on the transverse plane reveals cervical extension of the thymus (arrows) located anterior to the cervical trachea (asterisk) in a one-year-old boy. The thymic length was measured on the same plane in mm. Note the typical ‘starry sky’ appearance of normal thymus tissue.Fig. 1b. On the longitudinal plane, the cervically extended thymus tissue (arrows) is just below the thyroid lobe (asterisk).