EUS is a specialized test that combines upper endoscopy with sound waves to obtain ultrasound images of the esophagus, stomach, lower intestine, pancreas, liver and bile ducts. A thin, flexible tube with a built-in ultrasound probe is passed through the mouth or anus into area to be examined. The information obtained helps in diagnosing lumps or lesions,, and assists in the staging of various types of gastrointestinal tumors.