Primary hepatic and biliary tract tumors in dogs and cats: An overview
Since many of the clinical signs of hepatobiliary tumors are nonspecific, these tumors may be advanced at diagnosis. However, using the correct diagnostic tools, including cytology, tissue biopsy, and abdominal imaging, may lead to an earlier diagnosis and a better outcome.
Definitively diagnosing hepatobiliary tumors in dogs and cats
Figure 1. A ventrodorsal abdominal radiograph of a 7-year-old dalmatian presented for evaluation of elevated liver enzyme
activities and painless abdominal distention. A large cranial abdominal mass effect (white arrows) with caudal displacement
of the intestines is identified. Surgical biopsy confirmed a diagnosis of massive hepatocellular carcinoma.
In addition to performing complete blood counts, serum chemistry profiles, urinalyses, coagulation profiles, and hepatic function
tests when investigating possible hepatobiliary tumors in dogs and cats, you will need to perform diagnostic imaging. Cytology
and histology are needed to make a definitive diagnosis.
Imaging
Abdominal radiography and ultrasonography as well as advanced imaging modalities can be used to help identify an abdominal
mass.
Radiography
Figure 2. A lateral abdominal radiograph of a 7-year-old female spayed domestic shorthaired cat with a benign hepatic adenoma.
A subtle mass effect is present (white arrows).
In clinical practice, abdominal radiography is often the most convenient method for evaluating hepatomegaly or a palpable
abdominal mass. A common radiographic pattern associated with hepatobiliary tumors is a cranial abdominal mass with caudal
and lateral displacement of the stomach.1,2 Although a mass effect is infrequently detected with biliary carcinomas, most hepatomas (hepatocellular adenomas) and up
to 100% of hepatocellular carcinomas in dogs are discernible as a hepatic mass on radiographs (Figure 1).1-3 With feline hepatobiliary tumors, a mass effect is identified radiographically in only 60% of cases (Figure 2).4 Other radiographic findings consistent with hepatobiliary neoplasia in dogs include intraperitoneal fluid and mineralization
within the biliary system.1,5
Ultrasonography
Figure 3A & 3B. Similar ultrasonographic appearances of a (3A) benign canine hepatocellular adenoma and (3B) malignant canine
hepatocellular carcinoma (massive form). Both benign and malignant tumors produce sonographically evident mass effects, often
appearing as mixed echogenic lesions.
Abdominal ultrasonography is routinely used to identify hepatic parenchymal changes. When evaluating hepatic masses ultrasonographically,
quantify and localize the masses, characterize their echogenicity, identify their distribution (solitary or diffuse), and
look for evidence of cystic or vascular components. However, the ultrasonographic appearance of benign lesions such as nodular
hyperplasia and many malignant lesions may be similar in dogs (Figures 3A & 3B).6-8 The difficulties in ultrasonographically differentiating between benign and malignant hepatic lesions have been recently
reported. In one study, the ultrasonographic interpretation of 22 canine hepatic lesions resulted in a correct diagnosis in
only 50% of cases, with more than 35% of focal benign lesions being ultrasonographically classified as neoplastic.9 Although the ultrasonographic appearances of hepatic lesions are often nonspecific, some studies have attempted to characterize
ultrasonography findings most consistent with liver cancer. Some lesions identified ultrasonographically within visceral organs
may take on a halo effect and are called target lesions because of a hypoechoic rim surrounding an isoechoic to hyperechoic
center. Target lesions are associated with malignancy, with a positive predictive value of 74% for a focal lesion and 81%
for multiple lesions.10
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