The Role of Endoscopic Ultrasound in Pancreatic Diseases

16 Practical GastroenteroloGy • may 2012 IntroductIon Endoscopic ultrasound (EUS) was introduced in 1980, specifically for the purpose of imaging the pancreas.1 The indications for its use have since broadened, and EUS has now become an important tool for not only diagnostic purposes, but also to obtain tissue samples for histologic diagnoses in a variety of gastrointestinal disorders. Indeed, EUS has revolutionized the approach to pancreatic diseases. EUS offers a significant technical advantage over other imaging modalities such as trans-abdominal ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) in the evaluation of the pancreatic disorders, because the close proximity of the pancreas to the gastric and duodenal lumen allows EUS to obtain high-resolution images that are unobstructed by overlying bowel gas. In fact, EUS has been shown to be more sensitive in visualizing solid pancreatic tumors <3 cm as compared to a CT scan2 as well as in identifying small pancreatic lesions as compared to both a CT scan and MRI.3 Additionally, EUS is associated with fewer complications than endoscopic retrograde cholangiopancreatography (ERCP). Further, it can detect features of chronic pancreatitis in the pancreatic parenchyma and ducts that are not adequately visible in any other imaging modality.1 Another added benefit of EUS is its ability to biopsy pancreatic lesions in real time for tissue diagnosis.4 A review of the literature suggests that the overall diagnostic accuracy of EUS-FNA is 76%90% for pancreatic diseases, 82%-100% for lymph node and mediastinal diseases, and 38%-100% for gastrointestinal diseases such as submucosal tumors.5 Currently, the two dedicated instruments used for EUS examination are radialand linear-array ultrasound. The radial system uses a high-frequency (7-12 MHZ) scanner that produces a 360° image that is perpendicular to the long axis of the endoscope. Radial imaging is useful in staging disease processes in hollow visceral organs. However, a major limitation of this system is that FNA cannot be performed. Additionally, radial imaging has limited scanning depth secondary to its high frequency. Linear imaging, on the other hand, uses a lower frequency (5 to 7.5 MHZ) transducer. The linear scope obtains images parallel to the long axis of the endoscope. The benefits of the linear system include the use of a Doppler system and the ability to obtain FNA for tissue diagnosis. This system permits passage of a 19to 25-gauge FNA needle under real-time EUS guidance for tissue diagnosis.