Endoscopic ultrasonography (EUS) uses the technology of endoscopy to introduce high-frequency ultrasound probes into the upper or lower part of the gastrointestinal (GI) tract to visualize its wall and adjacent structures. EUS identifies and evaluates lesions occurring in the wall of the GI tract, in periluminal (mediastinal, abdominal, and pelvic) lymph nodes , pancreas, the left side of the liver, the spleen, left kidney, left adrenal gland, and at times masses in the most medial parts of lung . EUS is a highly accurate clinical test for the detection, staging, and optimal management of esophageal, gastric, colorectal, pancreatic, and biliary tumors as well as the evaluation of thick gastric folds and benign pancreatic disease.

In the last two decades, EUS -guided fine-needle aspiration (FNA) has empowered EUS as a tool that provides a cytologic diagnosis, being definitive and therapy-guiding for primary tumors such as pancreatic adenocarcinoma and for cancer staging , i.e., in the lung , pancreas, stomach , and esophagus . EUS-FNA changes the therapeutic strategy in up to 15 and 30 % of patients with clinical suspicion of upper GI tract and pancreatic malignancy, respectively. The information provided by EUS-FNA prevents unnecessary surgery in 30 % of patients who have a primary malignancy. In addition, EUS-FNA is minimally invasive, relatively inexpensive, and associated with low risk of complications . Thus, EUS-FNA has become a diagnostic strategy of choice for masses in such sites. Furthermore, EUS and EUS-FNA may prove to be valuable diagnostic modalities that change clinical management in selected critically ill patients in the intensive care unit; transient intraprocedural complications were reported in 9 % of interventions (6 of 63), predominantly related to brief oxygen desaturation. EUS and EUS-FNA have been proved useful in children as young as 5 years old with pancreas and mediastinal masses and when tissue was needed; the procedure is performed under general anesthesia and endotracheal intubation.

EUS-FNA provides an excellent sampling of lymph nodes , pancreatic tumors, and hepatic or left adrenal gland metastases. The overall sensitivity of EUS-FNA varies from 76 to 91 %, the specificity from 84 to 100 %, and the accuracy from 78 to 94 %. Statistical analysis of 5667 EUS-FNAs of various targets showed a specificity of 92.8 % (false positive rate 7.2 %, 27/377 cases with cytohistological correlation) due to epithelial cell contamination, EUS sampling error, and cytology misdiagnosis; scenarios included lymph node sampling in the setting of Barrett’s esophagus with dysplasia or early cancer, pancreas mass in chronic or autoimmune pancreatitis, reactive gastropathy, and nodal sampling for rectal cancer staging ; EUS-FNA samples may be contaminated with cellular elements carried over during transmural needle passage resulting in diagnostic difficulties. Recent analysis shows a pooled sensitivity of 85 % in the EUS-FNA of solid pancreatic masses. Cystic pancreatic lesions have a diagnostic rate of 66 % with the use of EchoBrush. Less favorable results are seen for EUS-FNA of cystic lesions of the pancreas (54 % sensitivity and 93 % specificity) and GI wall masses. Still, the overall accuracy of EUS-FNA in patients with mural masses, who had previously failed endoscopic standard forceps biopsy procedures, is 81 %. The nondiagnostic rate of EUS-FNA of pancreas is wide, ranging from 2 to 48 %; factors will be further discussed in Chap. 2.