An endoscopic ultrasound (EUS) is a direct ultrasound examination of the inside of a body cavity or organ, using an ultrasound transducer inside an endoscope (a small, flexible tube with a light and a lens on the end.) Dr. Joseph Romagnuolo, a gastroenterologist, gives an overview of the endoscopic ultrasound and explains how it is used to determine cancer staging, and reviews what the patient should expect for the procedure.