Figure 7a. Thymic cyst in an 18-year-old woman with stridor, hoarseness, and dyspnea. (a) Contrast-enhanced axial CT scan shows a hypoattenuating mediastinal mass (arrow) that displaces the trachea and supraaortic vessels anteriorly. (b) US scan shows an anechoic mass (M) extending up through the thoracic inlet behind the thyroid (TH). (c) Photomicrograph (hematoxylin-eosin stain) shows Hassall corpuscles.