EUS allows the execution of a high-resolution ultrasonography of the gastrointestinal wall (esophagus, stomach, duodenum, rectum) and of the adjacent structures (mediastinum, pancreas, extrahepatic bile ducts) through a digestive endoscope on the tip of which a smoll echographic transducer has been added.
Last generation sector scan echoendoscopes also permit the execution of an EUS-guided fine needle aspiration (FNA), for adding a cytological, biochemical and immunohistochemical analysis on the target lesion.
Since 1980, when EUS was born, hundreds of publications have confirmed the accuracy, the good clinical impact and the safety of this technique. The exam can be performed on outpatients under conscious sedation, it lasts 15-30 minutes, it is well tolerated and complications are few.
The principal indications of EUS are the following:

• locoregional staging of gastrointestinal malignancies (esophageal carcinoma, gastric carcinoma and lymphoma, rectal carcinoma): prognosis and therapeutic choices of these tumors depend on a precise staging. After the exclusion of distant metastases, EUS (better with FNA) allows a precise determination of both the neoplastic infiltration through the GI wall and the presence of lymph node metastases; an emerging indication is the post-neoadjuvant therapy evaluation. This improvement of diagnostic methods helps in deciding for each patient which is the most useful therapeutic approach among endoscopy, surgery or chemo-radiation; this increases the use of surgery with curative purpose minimizing thoracotomic or laparotomic inspections.
• diagnosis of gastrointestinal subepithelial lesions: both ultrasonographic pattern and wall layer of origin can suggest the differential diagnosis among these lesions such as leiomyoma, stromal tumor, neuroendocrine tumor, lipoma, pancreatic rest, cyst, varice. In doubtful cases Doppler pattern and FNA can help in getting the diagnosis.
• differential diagnosis of solid pancreatic masses (cancer, focal pancreatitis, neuroendocrine tumor, lymphoma, metastasis) according to ultrasonographic aspect and cytological confirmation; locoregional staging, after the exclusion of distant metastases in case of malignancy, for deciding between surgery or palliation.
• differential diagnosis of pancreatic cysts (seruos cystadenoma, mucinous cystadenoma, cystadenocarcinoma, IPMT, neuroendocrine or metastases with a liquid component, pseudocyst) according to ultrasonographic aspect, cytology and biochemistry; these technique can guide the decision among surgery, endoscopic therapy (for pseudocysts) or follow up.
• search of initial signs of chronic pancreatitis.
• diagnosis of common bile duct stones in patients with low-intermediate risk, before programming an ERCP.
• diagnosis and staging of common bile duct malignancy, with the possibility of getting a cytological specimen after a negative endoscopic brushing.
• staging of lung cancer: the easy access to posterior mediastinal lymph nodes makes FNA the optimal method to confirm the presence of metastases, rather than through broncoscopy or mediastinoscopy.
• operative EUS: EUS-guided drainage of pancreatic pseudocysts and EUS-guided neurolysis of celiac plexus (for pancreatic pain).