What is Endoscopic Ultrasound?
Endoscopic Ultrasound (EUS) combines endoscopy and ultrasound in order to obtain images and information about the digestive tract and the surrounding tissue and organs. Endoscopy refers to the procedure of inserting a long flexible tube via the mouth or the rectum to visualize the digestive tract (for further information, please visit the Colonoscopy and Flexible Sigmoidoscopy articles), whereas ultrasound uses high-frequency sound waves to produce images of the organs and structures inside the body such as ovaries, uterus, liver, gallbladder, pancreas, aorta, etc.
Traditional ultrasound sends sound waves to the organ(s) and back with a transducer placed on the skin overlying the organ(s) of interest. images obtained by traditional ultrasound are not always of high quality. In EUS a small ultrasound transducer is installed on the tip of the endoscope. By inserting the endoscope into the upper or the lower digestive tract one can obtain high quality ultrasound images of the organs inside the body.
Placing the transducer on the tip of an endoscope allows the transducer to get close to the organs inside the body. Because of the proximity of the EUS transducer to the organ(s) of interest, the images obtained are frequently more accurate and more detailed than the ones obtained by traditional ultrasound. The EUS also can obtain information about the layers of the intestinal wall as well as adjacent areas such as lymph nodes and the blood vessels.
Other uses of EUS include studying the flow of blood inside blood vessels using Doppler ultrasound, and to obtain tissue samples by passing a special needle, under ultrasound guidance, into enlarged lymph nodes or suspicious tumors. The tissue or cells obtained by the needle can be examined by a pathologist under a microscope. The process of obtaining tissue with a thin needle is called fine needle aspiration (FNA).
When is EUS useful?
Being a relatively new diagnostic tool the uses for EUS are still being developed and, presently, it is being utilized in some of the following situations:
- Staging of cancers of the esophagus, stomach, pancreas and rectum.
- Staging of lung cancer.
- Evaluating chronic pancreatitis and other masses or cysts of the pancreas.
- Studying bile duct abnormalities including stones in the bile duct or gallbladder, or bile duct, gallbladder, or liver tumors.
- Studying the muscles of the lower rectum and anal canal in evaluating reasons for fecal incontinence.
- Studying ‘submucosal lesions’ such as nodules or ‘bumps’ that may be hiding in the intestinal wall covered by normal appearing lining of the intestinal tract.
Staging of cancer is becoming an important use of EUS. The prognosis of a cancer victim is related to the stage of the cancer at the time of cancer detection. For example, early stage colon cancer refers to cancer confined to the inner surface of the colon before it is spread to adjacent tissues or distant organs. Therefore early stage colon cancer can be completely resected with good chances for cure. However, if cancer is detected at later stages, the cancer tissues have already penetrated the colon wall and invaded neighboring organs and lymph nodes, or have spread to distant organs such as liver and lungs. Complete surgical excision becomes highly unlikely. EUS can provide information regarding the depth of penetration of the cancer and spread of cancer to adjacent tissues and lymph nodes, information useful for staging.
What is the preparation for EUS?
Your doctor will want to know about your health status especially if you have any allergies, other significant health problems such as heart disease, lung disease, diabetes mellitus, etc.You will also be inquired about allergies to iodine or shellfish as, under certain circumstances, iodine containing contrast material may be used. If there is a possibility of fine needle aspiration (FNA), the doctor will want to check your blood for proper clotting. It is important to inform your doctor of any family history of bleeding problems or if you are taking medications that interfere with blood clotting (such as Coumadin) or platelet function (such as aspirin, Motrin, ibuprofen, Aleve, and other NSAIDs). The wisest is to inform you doctor of any prescription or non-prescription medication you might be taking. Antibiotics are usually not required except in patients with certain heart valve problems.
EUS is performed with sedation so you will not be able to return to work or to drive for 24 hours. It also means that you will need someone to take you home as this is usually an out-patient procedure.
You will need to have an empty stomach that means no oral intake for 6 or more hours. In case of a rectal EUS you will probably need to take some enemas or laxatives. In either case, full instructions will be given to you.