Exocrine pancreatic neoplasia

Neoplastic diseases of the exocrine pancreas can be primary or secondary. Primary neoplastic diseases of the exocrine pan­creas can be classified as benign or malignant. Pancreatic ade­nomas are benign tumors, which are usually singular and can be differentiated from pancreatic nodular hyperplasia (Fig­ure 8.12) by the presence of a capsule.

Etiology and pathogenesis

As in humans, the etiology of neoplastic conditions of the exocrine pancreas is unknown in dogs and cats. Neoplastic lesions can lead to the transposition of the organs of the cranial abdomen. However, these changes are subclinical in most cases and the diagnosis is often made as an incidental finding on necropsy examination. In a small number of human patients, the neoplastic growth can actually obstruct the pancreatic duct and cause secondary atrophy of the remaining exocrine pan­creas, leading to EPI. Even though such cases have not yet been reported in the cat and have only been anecdotally re­ported in a single dog, this possibility should be considered and patients presenting with clinical signs compatible with EPI should have their abdomen carefully palpated (Hill S, per­sonal communication, 2007).

In addition to a transposition of abdominal organs, adenocar­cinomas can also be associated with tumor necrosis when the tumor outgrows its vascular supply. Tumor necrosis in turn will cause a local inflammatory response, which can lead to the development of clinical signs of pancreatitis. Finally, exocrine pancreatic tumors can also spread to neighboring or distant organs.

Clinical signs and diagnosis

The presentation of canine and feline patients with exocrine pancreatic neoplasia is nonspecific. In a case series of 58 cats, the clinical signs most commonly reported were anorexia (46%), weight loss (37%), lethargy (28%), vomiting (23%), icterus (14%), constipation (9%), and diarrhea (3%).¹³¹ The clinical signs reported in other cases were polyuria, fever, de-

hydration, a distended cranial abdomen, and voluminous, pale, soft stools.¹³² Polyuria may be a clinical sign of concurrent diabetes mellitus. Obstructive jaundice has also been described in a cat with pancreatic adenocarcinoma.¹³³ A small number of dogs with multifocal necrotizing steatitis have been described that were ultimately diagnosed with pancreatic adenocarci­noma.¹³⁴ Finally, clinical signs related to metastatic lesions have also been reported in some cases of pancreatic adenocarci­noma and may present as lameness, bone pain, or dyspnea. Recently, several cases of paraneoplastic alopecia have been reported in cats with pancreatic adenocarcinoma.^135,136 The reported alopecia consisted of a generalized alopecia of the ventrum, limbs, and face in most cases, with diffuse zones of alopecia in the remaining cats.^135,136

Neutrophilia, anemia, hypokalemia, bilirubinemia, azotemia, hyperglycemia, and elevations of hepatic enzymes have all been reported in affected patients, but the results of routine blood tests may be unremarkable.^131,132 Elevations of serum hepatic enzyme activities and serum bilirubin concentration are identified most commonly.¹³⁷ Hyperglycemia, when present, is related to the concurrent destruction of pancreatic beta cells.

Radiographic findings are also nonspecific in most cases and include a decreased contrast in the cranial abdomen, suggest­ing peritoneal effusion into this area, transposition of the spleen caudally, and shadowing in the pyloric region.¹³² How­ever, in some cases abdominal radiographs can suggest the presence of a mass in the cranial abdomen.¹³⁷ Ultrasonographic examination of the abdomen is very helpful and in most cases a soft tissue mass can be identified in the region of the pan­creas;^44,137,139 although in many cases, continuation of the mass with pancreatic tissue cannot be conclusively identified.¹³⁷ Similarly, neoplastic lesions of the neighboring organs may be falsely presumed to be of pancreatic origin.⁴⁴ Also, patients with severe pancreatitis may show an ultrasonographic mass effect in the area of the pancreas that must not be confused with a pancreatic adenocarcinoma.^42,44

If peritoneal effusion is identified on abdominal ultrasound, a sample should be aspirated and evaluated cytologically. How­ever, in most cases, neoplastic cells do not readily exfoliate into the peritoneal effusion and no neoplastic cells are identi­fied on cytology. Fine needle aspiration or transcutaneous bi­opsy under ultrasound guidance can be attempted when sus­picious masses are identified and has been reported to be successful in approximately 25% of all cases.¹³⁷ The low suc­cess rate of fine needle aspiration is probably due to the lack of exfoliation of pancreatic adenocarcinoma cells.

Therapy and prognosis

Pancreatic adenomas are benign and theoretically do not need to be treated unless they cause clinical signs. However, since the final diagnosis of pancreatic adenocarcinoma is often made by way of a surgical biopsy, a partial pancreatectomy should be performed even in cases of suspected pancreatic adenoma. The prognosis in these cases is excellent.

Patients with a pancreatic adenocarcinoma often present at a late stage of the disease. Metastatic disease at the time of diag­nosis is common in dogs with this disease and has been re­ported to occur in 81% of cats.^131,1408 The most common sites of metastatic disease are the liver, abdominal and thoracic lymph nodes, mesentery, intestines, and the lungs; but various other metastatic sites have also been reported.¹³⁷ In those few cases where gross metastatic lesions are not identified at the time of diagnosis, surgical resection of the tumor may be at­tempted, but owners should be forewarned that clean surgical margins are only rarely achieved. Total pancreatectomy and pancreaticoduodenectomy, though theoretically possible, have not been described in dogs and cats with spontaneous disease. However, one report has detailed the management of dogs after experimental total pancreatectomy.¹⁴¹ Also, extrapolation from human patients suggests a high morbidity and mortality for these procedures.

Figure 8.14.

Pancreatic pseudocyst. This image shows the ultrasonographic image of a pancre­atic pseudocyst in a dog. The pseudocyst is characterized by a large almost com­pletely anechoic structure that is associated with the pancreas. In this patient, the volume of the pseudocyst was estimated at 237 ml. (Image courtesy of Dr. Kathy Spaulding, Texas A&M University, USA.)

Figure 8.15.

Pancreatic abscess. This image shows the ultrasonographic image of a pancreatic abscess in a dog. The abscess is characterized by a large hypoechoic structure. In most cases, pancreatic abscesses are more echoic than pseudocysts. However, in some cases, an abscess and a pseudocyst cannot be differentiated ultrasono­graphically. In contrast to humans, pancreatic abscesses in dogs and cats are usually sterile. (Image courtesy of Dr. Kathy Spaulding, Texas A&M University, USA.)

8.2.3