Endoscopic ultrasonography (EUS) is also known as endosonography. It has a great importance for gastroenterology and it combines both the ultrasound and endoscopic examination.
The examination is derived from the classic ultrasonography when the ultrasound probe is miniaturized and attached to the end of a flexible endoscopic device. This allows to insert the probe deep into the gastrointestinal tract and obtain ultrasound images from within the body. It is usually more accurate than conventional “external” ultrasound with the probe touching the patient's skin, because in endosonography, there are no anatomical structure putting resistance to the signal (subcutaneous fat, muscles, bones, etc.).
The preparation before the procedure depends on what endoscopic method is used. When the doctor performs the endosonography during upper GI endoscopy, the patient should not eat or drink about 6 hours before the examination. When the endosonography is performed during colonoscopy, the patient should fast for a longer period of time and use bowel-cleansing preparation (see the text about colonoscopy). Before the colonoscopic endosonography, the patient is also administered a tranquilizer to make the examination less unpleasant.
In gastroenterology, the endosonography is most commonly used in examination of the upper gastrointestinal tract. The probe is attached to endoscopic device and classic upper GI endoscopy is performed. In addition, the endosonography is less frequently performed during colonoscopy, typically for evaluation of lesions in rectum and left colon.
The examination allows to investigate a variety of mucosal and submucosal lesions of the gastrointestinal tube, particularly to evaluate the local extent (depth of mucosal invasion) of early forms of cancers (esophageal cancer, stomach cancer, rectal form of colorectal cancer) and to differentiate them from benign findings. The endosonography not only gives us information about the tumor mass, but also about affection of local deep lymph nodes. Endosonography is also great for evaluation lesions in nearby gastrointestinal organs such as liver, pancreas and gallbladder. EUS is used in diagnostics of unknown lesions located in pancreas (pancreas cysts, pancreatic cancer) as it enables the doctor to perform a targeted endoscopic biopsy guided by the EUS. The biopsy needle goes through the wall of gastrointestinal tract directly into the lesion.
Advantages and disadvantages
The examination is not invasive (except the necessity of introducing the probe into the gastrointestinal tube) and it is not associated with the use of harmful X-rays. On the other hand, the examination is not sot widely available and it depends on experience and expertise of the examiner.
Endoscopic ultrasonography is a valuable investigative method of hollow organs and their surroundings. It combines better visualization of gastrointestinal lesions with the possibility to take biopsies for histological examination.