Endoscopic ultrasonography, or EUS, allows your physician to examine the lining and walls of your upper and lower gastrointestinal (GI) tract. It is also helpful in evaluating internal organs that lie close to your GI tract including the gall bladder and pancreas. With the patient sedated, Dr. Castillo will advance a thin specialized flexible tube into the mouth (or anus if the lower GI tract is being examined). He will then perform an ultrasound from the inside of the GI tract (in contrast to traditional ultrasounds which are generally performed outside the body). The study is used to evaluation conditions such as abdominal pain, weight loss, and possible conditions related to gallstones. It is often used to further evaluate an abnormality described on CT scan or prior endoscopy, helping to clarify the nature of the problem and whether or not the abnormality invades into deeper layers of the GI tract. To prepare for the test, patients are usually instructed to no eat or drink for 6 hours prior to the exam. Possible complications of the test include bleeding or perforation. For more information, please refer to the ASGE (American Society for Gastrointestinal Endoscopy) website.