EUS is considered the best single diagnostic technique for the study of the pancreas. In the study of pancreatic tumors it is superior to CT and US, while in large lesions, disrupting pancreatic ducts it is comparable to retrograde cholangiography. In lesions smaller than 3 cm it presents the highest sensitivity (100%). Published reports have demonstrated EUS superiority in the diagnosis of small pancreatic cancers as compared to ultrasonography and CT. Therefore EUS has a fundamental role in the diagnosis of endocrine pancreatic tumours.
In spite of its high sensitivity, EUS has a lower specificity, being able to differentiate benign from malignant masses in only 76% of cases, ranging from 56% to 96%. In pancreatic lesions one the most difficult diagnostic problems is the differentiation between focal pancreatitis and pancreatic cancer. In doubtful cases definitive diagnosis can be obtained by EUS-guided FNAB. Villmann introduced EUS-guided FNAB in 1992 ; this procedure allows the cytological or histological sampling of suspected lesions of pancreas or gastrointestinal tract, or mediastinum. In doubtful cases definitive diagnosis can be obtained by EUS-guided FNAB: this procedure allows the cytological or histological sampling of suspected pancreatic lesions. With the help of EUS-guided FNAB the EUS accuracy for the diagnosis of pancreatic tumor has been improved, and a specificity of 90% and a positive predictive value as high as 100% have been reported. EUS-FNAB is a safe technique, with a complication rate ranging from 1 to 2%, and which is lower in the case of solid lesions (0.5%) than in cystic ones (14%).