Female, 21 years old, currently 35 weeks GA, with suspected thymic mass on ultrasound. A solid, homogeneous, relatively T2 hypointense soft tissue structure is present in the anterior mediastinum where is drapes the great vessels and heart most compatible with thymus tissue. The margins of this tissue are well defined and gently curved as would be expected for thymus. The tissue is at most mildly prominent, with a transverse diameter of 38 to 40 mm. This is reasonably close to the reported normative mean of 36 mm for a GA of 35 weeks as assessed by ultrasound (Cho et al., Ultrasound Obstet Gynecol 2007; 29:634-638). No evidence of any invasive features or cystic spaces is seen. The adjacent tissues of the upper thorax are within normal limits. The airway is visualized and is unobstructed from the level of the pharynx to the carina. No other neck masses are seen. The fetal thyroid is identified as a distinct structure and is normal.
No evidence of any pathologic neck or mediastinal mass lesion is seen. The thymus is identified in its normal anterior mediastinal position. The internal consistency of the gland is unremarkable. Size of the gland is in the range of upper normal. No aggressive or concerning features are seen. These findings most likely represent a normal or at most mildly hyperplastic thymus.The adjacent mediastinal structures are unremarkable. In particular, the airway is patent from the pharynx to the carina.