The pancreas is a large, relatively flat, white-to-pink-colored organ that develops from an outgrowth of the primitive foregut. It is a combined endocrine and exocrine gland in close association with the upper duodenum. During development, exocrine and endocrine elements are both derived from differentiation of duct epithelium. Depending on the species, the gross anatomical pattern of the pancreas presents as either a “mesenteric” or a “compact” type. The pancreas is invested by a very thin connective tissue capsule and divided into lobules, which in turn are formed from dense accumulations of exocrine glands that often surround islets of Langerhans. Individual lobules are defined by the thin connective tissue capsule extending into the parenchyma in the form of septa. These septa and associated interlobular connective tissues support blood and lymph vessels, nerves, ganglia, and pancreatic ducts. Arteries that supply the pancreas divide into arterioles within this space and distribute to individual lobules.

The pancreas is a difficult organ to evaluate by most abdominal imaging methods. In veterinary medicine, survey radiographs of the abdomen have traditionally been the initial imaging procedure of choice. Radiographic signs suggestive of pancreatic abnormalities include a soft tissue dense mass or loss of peritoneal detail in the right cranial abdomen and small amounts of duodenal gas accumulation indicative of functional ileus. An upper gastrointestinal tract series is helpful to confirm pancreatic masses that cause duodenal fixation or displacement, increased width of the cranial duodenal flexure, or thickening and deformity of the adjacent duodenum or stomach. However, the radiographic findings may be equivocal or normal in many cases of pancreatic disease.

Ultrasonography was one of the first modalities that enabled direct visualization of the pancreas in humans, and its use was quickly applied to animals. More recently, computed tomography, magnetic resonance imaging, and scintigraphy have played major roles in assessing pancreatic disease in humans. The preliminary use of these modalities to image the pancreas has also been described in animals.1-10 Fiberoptic technology has enabled the use of endoscopic retrograde cholangiopancreatography and endoscopic ultrasonography for pancreatic evaluation in humans. The potential applications and preliminary experience with endoscopic retrograde cholangiopancreatography and endoscopic ultrasonography of the pancreas have also been described in animals.11-17 The expense and availability of specialized equipment, as well as the need for anesthesia, have currently limited the routine use of these techniques in small animals. Ultrasonography is still the primary means for imaging the pancreas in the dog and cat because of its wider availability.

Ultrasonography complements but does not replace abdominal radiography for the work-up of the acute abdomen. Radiography is important for evaluating peritoneal detail, bowel patterns, and the displacement of viscera by large abdominal masses. Radiography is also useful for detecting gastrointestinal foreign bodies, free abdominal air, and bone abnormalities. Ultrasonography is better for evaluating pancreatic or other small abdominal masses, identifying focal fluid collections, and recognizing metastasis to adjacent organs or lymph nodes. In addition, ultrasonography is superior to radiography when there is a large amount of abdominal fluid. The discovery of a mass in the pancreatic region, with concurrent lymphadenopathy, metastasis, or other abnormalities, helps narrow the differential diagnosis and establish a prognosis for the acute abdomen. If necessary, material for cytologic analysis can be obtained from the pancreas, lymph nodes, or potential metastatic lesions by guided aspiration. Serial follow-up ultrasound examinations allow an accurate determination of treatment response.

Although there are many advantages to pancreatic ultrasonography, the technique also has significant limitations. These include poor visualization of the normal pancreas and interference from gas or barium in the gastrointestinal tract. Proper preparation of animals, judicious use of transducer pressure to displace overlying gas-filled bowel, and positional studies can usually overcome the limitations of bowel gas. Ultrasound examinations should always be performed before procedures causing aerophagia and before a barium series because of the high reflectivity of air and barium. The examination should be repeated if a diagnostic study cannot be obtained. The lack of abnormalities on an ultrasound examination of the pancreatic region does not exclude pancreatic disease, but it helps rule out significant anatomic abnormalities. In spite of these limitations, ultrasound has gained an important place in the diagnostic work-up of almost all cases of suspected pancreatic disease.

The normal canine or feline pancreas can be difficult to see as a distinct structure on ultrasound studies, but the surrounding anatomy, as described later, helps localize its position.18-23 Fat within and surrounding the pancreas is probably responsible for the high echogenicity of this region. In some cases, the pancreas is not visualized, but newer ultrasound equipment has allowed more frequent identification of the pancreas in dogs and cats. The acoustic output and gain settings of the scanner should be kept as low as possible to decrease overall reflectivity of the region and permit the greatest chance for visualizing the pancreas.

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