The superior sinus of the pericardium: CT appearance.

On computed tomography, a mass-like density is often observed, just posterior to the ascending aorta, that occasionally has been mistaken for mediastinal lymph node enlargement. Cadaver studies confirmed this retroaortic structure to be an extension of the pericardial cavity, the superior sinus. Current anatomic texts sometimes depict this space without description. Anatomic studies revealed the presence of a superior sinus in all of the 28 cadavers studied. The mean cross-sectional diameter of the sinus in a coronal plane was 2.5 cm with a range from 1.2 to 3.8 cm. Retrospective review of 116 consecutive adult chest computed tomographic examinations disclosed its presence in 49%. In 15% of the total, the size of the sinus was sufficiently large potentially to simulate mediastinal lymphadenopathy. This normal variant has a characteristic location, shape, and attenuation value by CT that should allow recognition and prevent misinterpretation.