endoscopic ultrasound
Endoscopic ultrasound (EUS) is a procedure combining the range of endoscopy with the diagnostic abilities of ultrasound. EUS is used in the imaging of the upper GI tract and surrounding structures as well as the respiratory tract (where it is referred to as endobronchial ultrasound - EBUS). A high-frequency transducer crystal is used, typically in the range of 12-20 Megahertz.
This article will be focusing on the upper GI use of EUS. For the respiratory tract, please refer to the article on endobronchial ultrasound (EBUS).
Radiographic features
Esophagus
Esophagus: in a healthy patient, five layers are seen:
- innermost layer (hyperechoic): superficial mucosal layer corresponding to the interface of the esophageal lumen and the mucosal layer
- second layer (hypoechoic): mucosal layer
- third layer (hyperechoic): submucosal layer
- fourth layer (hypoechoic): muscularis propria
- fifth layer (hyperechoic): esophageal adventitia
Esophageal cancer: endoscopic ultrasound can be used for local TNM staging of esophageal cancer to determine the local invasion of the tumor through the normal esophagus.
Pancreas
Endoscopic ultrasound can be used for aspiration (fine needle aspiration - FNA) of both solid and cystic pancreatic masses.
EUS has been shown to be the most sensitivity image modality on the detection of small functional pancreatic neuroendocrine tumors.
Biliary tree
EUS-guided biliary drainage has been shown as an alternative to percutaneous transhepatic biliary drainage when a conventional transpapillary endoscopic (ERCP) drainage has failed .
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