Two decades have elapsed since publication of the first papers describing the examination of the pancreas via the stomach and the duodenum using an ultrasound probe fixed to an endoscope tip. Initial attempts to image the pancreas in this fashion proved difficult and frustrating, but they were promising enough that instrument makers and gastrointestinal endoscopists persisted in developing increasingly effective devices.
Called "a marriage of inconvenience" in a 1987 editorial in the Lancet, endoscopic ultrasonography is now available in most academic medical centers and in many large community hospitals. The 13th International Symposium on Endoscopic Ultrasonography, to be held October 4-6, 2002, in New York City, will devote a major forum to issues involving the imaging of pancreatic neoplasms.
Endoscopic Ultrasound and the Pancreas
Endoscopic ultrasound has proved to be a good marriage after all. It is an accurate method for locoregional staging of gastrointestinal neoplasms and for evaluation of extrinsic mass lesions close to the gastrointestinal tract. The entire pancreas, including the uncinate process, head, body, and tail, can usually be scanned through the stomach and the duodenum. Because the transducer is close to the pancreas, interference from the abdominal wall and bowel gas is eliminated. Higher-frequency ultrasound with shorter penetration can be used, producing images with greater clarity and detail. The development of endoscopic ultrasound-guided fine-needle aspiration (FNA) of the pancreas has provided a new means by which to obtain cytologic material and tumor markers and to improve diagnostic yield and accuracy.
Drs. Levy and Wiersema have written a superb review of the current experience and evidence supporting the use of endoscopic ultrasound in the diagnosis and staging of pancreatic cancer. They present extensive data indicating that the technique is very accurate for the detection of pancreatic masses, identifying more than 90% of them. The negative predictive value is in the same range, so that a negative endoscopic ultrasound examination of the pancreas is very helpful when body imaging with computed tomography (CT) or magnetic resonance imaging (MRI) is equivocal. The authors also provide recent evidence that endoscopic ultrasound remains helpful in detecting or ruling out pancreatic masses even with the improvements in helical CT scanners and MRI technology.
Guiding Management Decisions
A persistent problem for endoscopic ultrasound imaging is the difficulty in differentiating a neoplastic mass in the pancreas from focal pancreatitis. The difficulty is compounded because chronic pancreatitis increases the risk of developing carcinoma of the pancreas, and because pancreatic cancers often create a surrounding inflammatory and desmoplastic reaction. Fine-needle aspiration using endoscopic ultrasound guidance has been a major advance in helping to solve this dilemma. While a negative cytology does not rule out the possibility of a malignancy, a positive cytology is highly specific and can help guide a patient to surgical or combined-modality therapies.