Endoscopic Ultrasonography in Benign Pancreatic Disease

Abstract

Since 1980, when endoscopic ultrasonography (EUS) was first developed, it has emerged as a highly accurate test for imaging pancreatic disease.⁵³ EUS combines and modifies the techniques of endoscopy and ultrasonography to diminish the distance between the ultrasound source and the pancreas to provide high-resolution images. In EUS, an ultrasound transducer is incorporated into the tip of a fiberoptic endoscope. Thus, bones, adipose tissue, and air-filled structures, which limit sound wave imaging clarity, can be avoided. In addition, the higher-frequency 7.5- and 12.0-MHz sound waves used in EUS, compared with 3.5 MHz used in standard sonography, result in a greater resolution for EUS. In addition, as with all real-time sonography, the sound wave imaging plane can be oriented at any angle by turning the probe, so as to bring the area of disease into optimal focus, rather than being limited to the parallel sections that are usually 1 cm apart, as is the case for CT scanning and MR imaging. By permitting the visualization of very small lesions, ductal abnormalities, and calcifications, a dramatic improvement in disease characterization and tumor-node-metastasis (TNM) staging over other imaging techniques is now possible. The high accuracy of real-time EUS is primarily the result of its unsurpassed resolution of the parenchyma of the pancreas and its capability to allow for evaluation and integration on the same examination of mucosal, vascular, ductal, and parenchymal abnormalities caused by disease. To obtain information about these four types of abnormalities, four separate tests would otherwise be required: (1) endoscopy to evaluate the mucosa, including the ampulla of Vater; (2) venogram or arteriogram for vascular anatomy; (3) endoscopic retrograde cholangiopancreatography (ERCP) for the pancreatic and bile ducts; and (4) CT scanning, MR imaging, or standard sonography for the parenchyma and surrounding lymph nodes.

Compared with EUS, a successful ERCP provides superior imaging of the common bile duct (CBD) and pancreatic duct; however, when ERCP does not visualize a part of the pancreatic duct or CBD, this area usually is seen well on EUS. Even pancreatography or cholangiography can be performed with EUS-guided puncture and injection of contrast medium into the desired duct when ERCP is unsuccessful and standard EUS does not adequately visualize the ducts.

Successful execution of EUS requires specific equipment and special technique. The Olympus radial and linear imaging units (Olympus America, Inc., Melville, NY) are used widely and considered the most reliable. The head of the pancreas can be imaged by placing the transducer of the echoendoscope in the duodenum. From this location, the uncinate and head of the pancreas up to the neck can be imaged. From the stomach, the pancreatic tail, body, and neck can be imaged. Only limited imaging of the head can be accomplished from the stomach. Accurate imaging of the superior mesenteric vein and artery can be accomplished only from the descending duodenum with a radial echoendoscope. The entire pancreas can be imaged by EUS in almost all patients unless altered anatomy or stenosis of the intestinal lumen is present.

Typically, EUS is used in three situations for the detection and diagnosis of benign pancreatic conditions: (1) chronic pancreatitis; (2) cystic lesions; and (3) diseases related to lithogenic bile, such as stones, sludge, and chronic inflammation. The two primary therapeutic uses of EUS are (1) the aspiration and drainage of a cyst or pseudocyst and (2) the administration of nerve blocks.