Introduction

A definitive diagnosis of pancreatitis can be quite challenging in small animals. This may in part be due to the wide clinical range of cases (patients may be subclinical or may present with peracute disease), the vague clinical signs seen in cats, and a traditional lack of diagnostic tests that are both sensitive and specific for pancreatitis.

Traditionally, it has been thought that in dogs approximately 2/3 of pancreatitis cases are acute, while in cats 2/3 have been reported to have chronic disease.¹ Chronic pancreatitis is more difficult to assess sonographically than acute due to lack of secondary changes such as a hyperechoic peripancreatic mesentery, severe enlargement and decreased echogenicity of the pancreas as well as free fluid and duodenal rigidity. The diagnosis of feline pancreatitis is a complicated one and should be based on a combination of clinical signs, blood results including feline pancreatic lipase inhibition (fPLI) and ultrasound. The sensitivity of ultrasound alone for diagnosing pancreatitis in cats is low, ranging from 11-35%. Currently, there are no universally agreed upon guidelines or parameters for diagnosing feline pancreatitis with ultrasound. However, attention to pancreatic size, echotexture and peri-pancreatic changes and the presence of multi-organ disease help support the diagnosis.

Clinical Signs

Cats, even with severe pancreatitis, present with nonspecific clinical signs. Especially remarkable is the low incidence of vomiting and abdominal pain, both of which are common clinical signs in human and canine pancreatitis patients. Recently, assays for measurement of pancreatic lipase immunoreactivity in dogs and cats (cPLI and fPLI, respectively) have been developed and validated.^2,3 Many different cell types in the body synthesize and secrete lipases. In contrast to catalytic assays for the measurement of lipase activity, use of immunoassays does allow for the specific measurement of lipase originated from the exocrine pancreas.

Imaging

Transabdominal Ultrasound

Ultrasonography is currently one of the most commonly used tools for the diagnosis of pancreatitis in dogs and cats. Ultrasound is widely available today, but the sonographic examination of the pancreas is highly user dependent. An excellent knowledge of anatomy as well as experience is required to both locate the pancreas and interpret its appearance.⁴ Excessive gas in the gastrointestinal tract, as well as deep thoracic conformation, may inhibit the visualization of all parts of the pancreas. Obese animals pose an additional barrier even for experienced sonographers. Furthermore, animals with pancreatic disease often have abdominal pain and resent transducer pressure in the region of the pancreas and analgesia and sedation may be necessary. These limitations have provoked interest in other imaging modalities such as computed tomography, magnetic resonance imaging, nuclear scintigraphy, contrast enhanced sonography and endosonography. However, these methods are not yet well established in veterinary medicine.

The sonographic appearance of chronic pancreatitis in dogs and cats has not been well described. The pancreas may be of normal size or enlarged with a heterogenous appearance. Hyperechoic foci with acoustic shadowing may represent mineralizations. In cats, multiple hypoechoic round foci of a few millimeters in diameter may also be recognized. These may represent nodular hyperplasia or dilated pancreatic ducts.⁵ Cavities of the pancreas in dogs and cats are typically either due to abscesses or pseudocysts and appear as anechoic or hypoechoic cavities, possibly with a thickened wall.⁶

A number of investigators have attempted to assess the sensitivity and specificity of ultrasound compared to other imaging modalities for diagnosing pancreatitis in cats, however, with greatly varying results.^7,8,9 Ultrasound will most likely remain one of the most important diagnostic tools in both dogs and cats as it allows not only assessment of the pancreas, but also that of other organs that may be involved in the inflammatory process.

Examination of the feline pancreas is similar to that in dogs. Identifying important landmarks is critical to localizing the pancreatic limbs as the pancreatic parenchyma can be difficult to differentiate initially from the surrounding mesentery. It may have indistinct margins and be isoechoic with the mesentery in the normal situation. In cats, the left lobe of the pancreas and body are easier to see than the right (the opposite in dogs). Pancreatic ducts are easier to see in cats than dogs. Also, the major duodenal papilla is the common entrance of the pancreatic and common bile duct in cats, which is not the case in dogs.

The main landmark for identifying the left lobe and body in the cat is the portal vein. The pancreatic body lies directly ventral to the portal vein caudal to the stomach. The left lobe is caudal to the stomach and cranial to the transverse colon on the left side of the portal vein. It may continue caudally for a small distance to the level of the splenic hilus. The pancreatic duct is more commonly identified in cats and is seen as a small anechoic tubular structure in the body and left pancreatic lobe. The right lobe of the pancreas is small in the cat and is more difficult to identify. It is adjacent to the duodenum and follows it caudally. A small pancreatic duct can also be identified in it. The major duodenal papilla appears as a small nodule attached to the duodenal wall close to the cranial flexure.

The following are parameters that should be assessed when investigating the feline pancreas:

 Pancreatic size:

 The left and right limbs as well as the body should be examined and measured for thickness in the sagittal plane.

 Normal: Body: 0.5-0.9 cm thick, Left lobe: 0.4-1.0 cm thick, right lobe: 0.3-0.6 cm.

 Abnormal: In acute disease, the pancreas may become enlarged as in dogs. However, this finding is much more inconsistent in cats. In chronic disease the pancreas may be of normal size or smaller. Unremarkable changes do not rule out pancreatitis in cats.

 Pancreatic size does not increase with increasing age.

 Pancreatic echogenicity:

 Normal: Iso- to hypoechoic with the mesentery.

 Abnormal: The pancreas usually becomes hypoechoic in acute disease. In chronic disease the pancreas may have a normal, hypo or hyperechoic appearance.

 Pancreatic echogenicity does not change with increasing age.

 Pancreatic echotexture:

 Normal: Finely textured.

 Abnormal: Often the pancreas appears heterogeneous. It can become nodular with irregular borders. Nodular hyperplasia has the appearance of small hypoechoic distinct nodules throughout the parenchyma. It is commonly seen in older cats. Nodules may be up to 1cm in diameter and the pancreas may be enlarged.

 Pancreatic duct size:

 Normal: 0.5-2.5mm diameter.

 Too little is known about the size of the duct in disease. However, there is a slight increase in size of the duct in older cats.¹⁰

 Liver, hepatobiliary system and small intestines:

 In cats, the liver and small intestines may also be affected in a combined set of inflammatory diseases called 'triaditis'. This is due to the presence of cholangiohepatitis and inflammatory bowel disease along with the pancreatitis. The intestinal walls may appear mildly thickened and the mucosa hyperechoic. The muscularis layer may appear thickened and hypoechoic. The liver may be enlarged, diffusely hyperechoic or hypoechoic. Hepatic tissue sampling is indicated in such instances, as well as intestinal biopsy, to rule out neoplasia.

Endosonographic Ultrasound

Endosonography (EUS) of the pancreas via a transgastric approach allows excellent visualization of the entire pancreas in cats since interference with air is prevented and the transducer can be brought into close proximity with the pancreas.¹¹ At the University of Bern, Switzerland, the authors have examined a series of both normal cats and those suspected of having pancreatitis. EUS could be performed with repeatable results in normal cats and the entire pancreas could be easily visualized. This was also the case for cats with pancreatitis where EUS allowed superior resolution of the pancreas compared to transabdominal ultrasound. Nodules, abscesses, irregular borders and inhomogeneities of the pancreas, not detected by transabdominal ultrasound, could be identified with EUS.

Contrast Enhanced Ultrasound

One study has described the appearance of contrast enhanced Doppler ultrasound in cats with histologically proven pancreatitis. It was shown that cats with pancreatitis have an increased vascularity and perfusion and abnormal vascular anatomy could be shown in two cats with pancreatic tumors. More work is warranted in this promising field.

References

1.  Isler D. Uebersicht ueber die wichtigsten Erkrankungen bzw. Todesursachen der Katze. Sektionsstatistik 1965-1976. 1978.

2.  Steiner JM, Wilson BG, Williams DA. Development and analytical validation of a radioimmunoassay for the measurement of feline pancreatic lipase immunoreactivity in serum. Can J Vet Res 2004; 68(4): 309-314.

3.  Steiner JM, Teague SR, Williams DA. Development and analytic validation of an enzyme-linked immunosorbent assay for the measurement of canine pancreatic lipase immunoreactivity in serum. Can J Vet Res 2003; 67(3): 175-182.

4.  Etue SM, Penninck DG, Labato MA, Pearson S, Tidwell A. Ultrasonography of the normal feline pancreas and associated anatomic landmarks: a prospective study of 20 cats. Vet Radiol Ultrasound 2001; 42(4): 330-336.

5.  Wall M, Biller DS, Schoning P, Olsen D, Moore LE. Pancreatitis in a cat demonstrating pancreatic duct dilatation ultrasonographically. J Am Anim Hosp Assoc 2001; 37(1): 49-53.

6.  Hines BL, Salisbury SK, Jakovljevic S, DeNicola DB. Pancreatic pseudocyst associated with chronic-active necrotizing pancreatitis in a cat. J Am Anim Hosp Assoc 1996; 32(2): 147-152.

7.  Saunders HM, VanWinkle TJ, Drobatz K, Kimmel SE, Washabau RJ. Ultrasonographic findings in cats with clinical, gross pathologic, and histologic evidence of acute pancreatic necrosis: 20 cases (1994-2001). J Am Vet Med Assoc 2002; 221(12): 1724-1730.

8.  Gerhardt A, Steiner JM, Williams DA, Kramer S, Fuchs C, Janthur M, Hewicker-Trautwein M, Nolte I. Comparison of the sensitivity of different diagnostic tests for pancreatitis in cats. J Vet Intern Med 2001; 15(4): 329-333.

9.  Forman MA, Marks SL, De Cock HEV, Hergesell EJ, Wisner ER, Baker TW, Kass PH, Steiner JM, Williams DA. Evaluation of serum feline pancreatic lipase immunoreactivity and helical computed tomography versus conventional testing for the diagnosis of feline pancreatitis. J Vet Int Med 2004; 18(6): 807-815.

10. Larson MM, Panciera DL, Ward DL, Steiner JM, Williams DA. Age-related changes in the ultrasound appearance of the normal feline pancreas. Vet Radiol Ultrasound 2005; 46(3): 238-242.

11. Morita Y, Takiguchi M, Yasuda J, Kitamura T, Syakalima M, Hashimoto A. Endoscopic and transcutaneous ultrasonographic findings and grey-scale histogram analysis in dogs with caerulein-induced pancreatitis. Vet Q 1998; 20(3): 89-92.