Pancreatitis in Dogs and Cats

Pancreatitis refers to inflammation of the exocrine pancreas and is the most common exocrine pancreatic disorder in dogs and cats, being divided into acute or acute necrotizing, and chronic [1–5]. The differences between acute and chronic pancreatitis are histologic and not necessarily clinical.

Acute pancreatitis is associated with varying degrees of inflammation, necrosis, and edema, whereas chronic pancreatitis histologically demonstrates irreversible and progressive fibrosis and acinar loss [2–5]. Although several causes have been reported, in most cases it is considered idiopathic [2–4]. Histopathology is the gold‐standard method of diagnosing pancreatitis but is not commonly performed due to its invasive nature. A presumptive diagnosis is usually made by a combination of clinical signs and clinicopathologic and diagnostic imaging findings. Pancreatitis has been reported to be one of the most common causes of portal vein thrombosis in dogs and CT angiography is the gold‐standard method for the diagnosis of portal vein thrombosis [6, 7].

The major radiographic sign of pancreatitis is loss of peritoneal detail with increased soft tissue opacity in the right cranial abdomen which is a result of focal peritonitis (Figure 26.7). Other signs include a mass effect in the right cranial abdomen and a persistent gas‐filled proximal descending duodenum, termed a “sentinel loop sign.” The proximal duodenum may also be displaced ventrally or laterally, appearing to have a broader curvature, and the pylorus of the stomach may be displaced toward the left. However, none of these signs are specific for pancreatitis and radiographs may appear normal.

Ultrasound is usually the imaging modality of choice to diagnose pancreatitis in dogs and cats, but CT has been performed more often recently. Ultrasound findings in acute pancreatitis include an enlarged, possibly mass‐like pancreas with hypoechoic parenchyma, adjacent hyperechoic mesentery, and peritoneal effusion [18–10] (Figures 26.8–26.15). With pancreatic necrosis, there may be irregular hypoechoic and hyperechoic areas and nonenhanced pancreatic tissue [11] (Figure 26.16). The hypoechoic areas within the pancreas are usually caused by inflammation, hemorrhage, necrosis or edema, and the hyperechoic areas are usually caused by fibrosis [2]. Other ultrasound findings include cystic‐like or cavitated lesions, dilation of the pancreatic duct, especially in cats, duodenal or gastric thickening with or without loss of layering and corrugation of the duodenum, and extrahepatic biliary obstruction [1, 9, 10] (Figure 26.10). It is important to remember that dilation of the pancreatic duct in cats can also be associated with aging [12, 13]. Ultrasound may also be normal in cats and dogs and may be normal in the initial stages in dogs [9, 10].

A study evaluating ultrasonographic monitoring in 38 dogs with clinically suspected pancreatitis found that approximately one‐third of the dogs did not have ultrasound findings of acute pancreatitis at the first ultrasound but did on the second examination performed 40–52 hours later [14]. The authors suggested waiting at least 52 hours after admission to perform ultrasound on a dog suspected of having acute pancreatitis [14]. In a study evaluating 25 cats with B‐mode and contrast‐enhanced power and color Doppler ultrasonography of the pancreas, vascularity and blood volume for all Doppler methods were significantly higher in cats with pancreatic disease compared to normal cats [15]. B‐mode ultrasound findings in the diseased cats included hypoechogenicity of the pancreas compared to the liver, irregular contour, presence of masses, nodules or cysts within the pancreas, inhomogeneous pancreas, hyperechoic mesentery, and free fluid. Eight cats in the study had pancreatitis, four had nodular hyperplasia and four had neoplasia. Also in this study, significantly higher values were found with postcontrast compared to precontrast color or power Doppler ultrasound [15].

In a study evaluating contrast‐enhanced ultrasound (CEUS) of the pancreas in healthy dogs and dogs with acute pancreatitis, the mean pixel and peak intensity of the pancreatic parenchyma in dogs with pancreatitis was significantly higher than that of dogs with normal pancreas, suggesting CEUS can be useful for diagnosing canine pancreatitis and pancreatic necrosis [16]. In a similar study evaluating CEUS in 23 dogs with naturally occurring pancreatitis and 12 normal dogs, of all the parameters evaluated, a significant difference was found only for peak time, with dogs with pancreatitis having a prolonged peak time compared to control dogs [17]. The study suggests CEUS can be used in dogs for the detection of pancreatic perfusion changes as a possible sign of pancreatitis.

Computed tomographic findings are similar, including an enlarged pancreas with ill‐defined borders and homogeneous or heterogeneous enhancement, adjacent peritoneal effusion possibly with fat stranding, thickening of the adjacent duodenum and/or gastric wall, dilated gall bladder and biliary tract due to compression and obstruction by the enlarged pancreas [8, 10, 18] (Figures 26.14–26.17). In a study evaluating the use of CT angiography in sedated dogs with suspected pancreatitis, an enlarged homogeneously or heterogeneously enhancing pancreas with ill‐defined margins were the main findings [18]. In addition to these findings, three out of 10 dogs had portal vein thrombi. Not surprisingly, the portal vein thrombi seen with CT was not found on US on any of the dogs (given the challenge of examining the portal vein with US in dogs). The authors also found that three out of four dogs with heterogeneous enhancement had overall poorer outcome compared to the dogs with homogeneous enhancement, concluding that the heterogeneous enhancement may correspond to necrotic or fibrotic nonenhancing regions in the pancreas. However, the overall number of dogs with heterogeneous enhancement is very small and a larger number of cases would need to be studied for meaningful conclusion of this finding [18].

Another study compared the use of computed tomography angiography (CTA) with ultrasound in the diagnosis of acute pancreatitis in dogs and concluded that CTA did not significantly identify pancreatitis better than ultrasound. However, it allowed visualization of the entire pancreas and detected portal vein thrombosis and biliary mineralization significantly better than ultrasound [10].

Acute pancreatitis has been associated with pulmonary complications in dogs [19, 20]. A study evaluated 26 dogs presenting with acute pancreatitis and found 21 of the 26 had clinical and radiographic signs of pulmonary disease, including alveolar and interstitial pattern, indicative of acute lung injury or pneumonia [20]. In a study evaluating the accuracy of CT for the diagnosis of feline pancreatitis, only two of the 10 cats had CT changes consistent with pancreatitis, which were described as enlarged pancreas and reduced contrast in the surrounding fat in one of the cats [21]. In this study, visualization of the pancreas was considered difficult on CT and not possible without intravenous contrast administration. In a recent study evaluating 21 cats with pancreatitis, the pancreas was seen on CT in 18 out of 19 cats, but differences in pancreatic dimensions were not seen in cats with pancreatitis compared to normal cats. Measurements included diameter, contour, enhancement, and pre‐ and postcontrast density [8]. These two studies suggest lack of support for the use of CT in the diagnosis of pancreatitis in cats [8, 21].

There are very few reports on the use of magnetic resonance imaging (MRI) for evaluation of the pancreas. With MRI, the pancreas is assessed by evaluating the intensity changes on T1‐ and T2‐weighted sequences, the contrast enhancement, the presence of pancreatic and common bile duct dilation, and by evaluating the surrounding soft tissues for the presence of fluid and inflammation indicating peritonitis. Magnetic resonance cholangiopancreatography has been used to image the biliary tract and pancreatic duct in normal cats and in cats with cholangitis and pancreatitis [22]. MRI findings in cats with pancreatitis included enlargement, pronounced signal intensity abnormalities with T1 precontrast hypointense and T2 hyperintense pancreatic parenchyma (normal pancreas in cats is T1 hyperintense and T2 hypointense), contrast enhancement, and dilated pancreatic duct [22].

The diagnosis of chronic pancreatitis is very challenging, and the differentiation of acute and chronic pancreatitis may also be challenging [1–4]. With chronic pancreatitis, radiographs are usually normal. With ultrasound, the pancreas may be normal or decreased in size, with mixed echogenicity, nodular lesions and hyperechoic shadowing lesions corresponding to fibrosis and/or mineralization [1, 9, 10]. In cats, enlargement or irregularity of the pancreatic ducts may be seen as well as dilated common bile duct if there is partial or complete common bile duct obstruction. Pancreatitis in cats may be seen associated with hepatic lipidosis, cholangitis, diabetes mellitus or inflammatory bowel disease [3, 4].

Concurrent pancreatitis, inflammatory bowel disease, and hepatic lipidosis is a medical condition in cats called triaditis [3, 4]. Ultrasound signs associated with triaditis in addition to those seen with pancreatitis include diffuse hyperechoic liver and changes in the small intestine layering and/or thickness (see Triaditis below).

Pancreatitis cannot be reliably differentiated from pancreatic neoplasia based on imaging alone and sampling is needed for definitive diagnosis.