Midline pericardial cyst in the posterior mediastinum: sonographic and computed tomographic correlation.

A chest radiograph revealed an incidental finding of a large mediastinal mass located in the midline posterior to the lower aspect of the heart. The computed tomogram and sonographic examinations of the chest showed the mass to be cystic in nature, contiguous with the heart, and anterior to the displaced distal esophagus. At surgery this proved to be a pericardial cyst. The unusual location of this entity, which has never before been documented, now behooves us to include pericardial cyst and diverticulum in the differential diagnosis of mediastinal masses, posterior to the heart.