Department of Equine and Small Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki
Imaging the 'hidden organ' has always been a challenge due to the anatomical position and the tissue consistency of the canine pancreas. However, visualizing the pancreas is essential to assess morphologic changes of the organ. Imaging techniques for the diagnosis of pancreatic diseases have the following four aims1:
Diagnosis of a pancreatic disease
Assessment of its spatial extension
Differential diagnosis and etiology of the disease
Assessment of indication and viability of surgery
Different imaging techniques that have been used in dogs are radiography, abdominal ultrasound, contrast-enhanced computed tomography (CT), endosonography, endoscopic retrograde pancreatography (ERP) and laparoscopy with pancreatic biopsy. Radiography has proven to be the least sensitive and specific technique to diagnose pancreatic diseases.
Abdominal ultrasound is of low invasiveness, relatively easy accessible and allows good visualization of the normal and diseased canine pancreas when high quality equipment is used by an experienced ultrasonographer.2 Ultrasound can contribute to the diagnosis of inflammation (necrosis), pseudocyst or tumor especially when it is combined with fine needle aspiration for cytology or fluid aspiration from pancreatic pseudocysts.3 Furthermore, ultrasonographic examination can be repeated arbitrarily.1
However, the close association of the pancreas with the stomach and duodenum causes limitation for the sonographic visualization of the organ. Intragastric and intraduodenal gas can disturb or even prevent the imaging of the whole pancreas. Other negatively influencing factors are abdominal pain, and difficulties in sonographic differentiation between necrosis and tumor or between acute and chronic pancreatitis.2 Improvement is expected by using contrast enhanced ultrasound (CEUS), a technique that allows us to assess the extent of morphological changes and to differentiate better between inflammation and neoplasia.4
Contrast enhanced computed tomography (CT) is widely used to diagnose pancreatic diseases in people. It is indicated to differentiate acute from chronic pancreatitis, to assess the severity and extent of inflammatory and neoplastic processes, and to plan surgical procedures. In dogs, CT has been used successfully to describe the appearance of the normal pancreas and to diagnose acute and chronic pancreatic diseases with high accuracy.5-9
However, CT has not been established for routine use in dogs due to difficulties in accessibility, necessity for general anesthesia, and high examination costs.
In humans, endosonography is indicated to search for very small tumors and metastasis in liver and pancreas that can not be visualized by abdominal ultrasound or CT. The technique helps to assess the actual size and localization of tumors due to high sensitivity and the possibility for exact sampling of biopsies out of sonographically abnormal areas. It also helps to assess the necessary extent of surgical interventions.10 The technique has been used in dogs for a limited number of studies that proved its usefulness for imaging the normal and diseases pancreas.11-13 However, endosonography will not be widely available for canine patients due to very high equipment costs.
Endoscopic Retrograde Pancreatography
Endoscopic retrograde pancreatography (ERP) combines endoscopy and fluoroscopy. It has been used for decades in people for diagnosing and staging chronic pancreatitis and pancreatic carcinoma by assessing contrast images of the pancreatic duct system.14 Recent studies in healthy dogs revealed that ERP is feasible also in this species. It was possible to establish reference images and values for the length and diameter of the accessory pancreatic duct for healthy beagles.15 The reported success rate for ERP in dogs with chronic gastrointestinal problems was 70% at the time of the study. Abnormal ERCP findings of pancreatic ducts were documented in 2 dogs with proven pancreatic acinar atrophy.16 The assessment of possible negative side effects of ERP revealed a temporary increase of pancreatic enzyme values in serum but no clinical signs of acute pancreatitis either in healthy dogs or in dogs with chronic gastrointestinal problems.15,17
Laparoscopy is an excellent tool to diagnose and differentiate pancreatic diseases such as chronic pancreatitis, pancreatic adhesions to adjacent organs, and partial pancreatic acinar atrophy. Side effects are minimal and pancreatic biopsy has not been reported to cause systemic complications such as acute pancreatitis. The technique can be recommended especially to diagnose chronic pancreatitis.18-23 Relative high initial investment costs are the only disadvantage of laparoscopy.
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