A 74-year-old man underwent transesophageal echocardiography to evaluate the possibility of dissection of the descending aorta. The study demonstrated a round lumen that contained an echogenic mass mimicking aortic aneurysm with thrombus. However, computerized tomographic scanning identified the lumen as the pleural cavity containing a collapsed lung. The esophagus was on the right side of the spine, and the transesophageal technique could not visualize the descending aorta.