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.
Figure 4. A transverse CT image of malignant canine hepatocellular carcinoma (massive form) provides additional preoperative
information about the feasibility of surgical resection. The tumor (hypointense signal) involves more than 50% of the ventral
aspect of the liver.
Advanced imaging modalities such as CT (Figure 4) and MRI are used in human medicine to better detect and localize hepatic lesions. MRI is an emerging modality in veterinary
medicine, and a recent study in dogs demonstrated differentiation between malignant and benign hepatic lesions with a 100%
sensitivity and 86% specificity. These MRI results support the notion that advanced imaging can be used to accurately differentiate
between benign and malignant hepatic lesions in dogs and will perhaps, in the future, reduce unnecessary biopsy of benign
liver lesions.11
Cytology
Cytologic examination of a sample of the hepatic mass obtained by fine-needle aspiration can provide a definitive diagnosis
with minimal complications (Figure 5). However, the sensitivity of cytology for diagnosing hepatic disorders is reported to be only 33.3%, which is much lower
than the sensitivity of cytology for diagnosing disease processes of other anatomical sites.12 Although hepatic cytology may have low sensitivity for accurately diagnosing nonneoplastic diseases, a good correlation
exists between cytology and histology for neoplastic processes affecting the liver. The accuracy of cytology for diagnosing
hepatic neoplasia is supported by two independent studies, which demonstrate 70% to 100% correlation between cytology and
histology for diagnosing liver epithelial tumors.3,13
Histology
Figure 5. A photomicrograph of a fine-needle aspirate from a large solitary liver mass in a 9-year-old male castrated Labrador
retriever presented for evaluation of abdominal discomfort and inappetence. The cells have a moderate rim of basophilic cytoplasm
with a large round nucleus and prominent nucleoli, consistent with a well-differentiated hepatocellular carcinoma (Wright’s
stain; 500X). (Photograph courtesy of Dr. Anne Barger.)
Despite the ease and relative accuracy of hepatic cytology for identifying neoplastic processes, histologic examination may
be required for the definitive diagnosis of tumors that are poorly exfoliative. With ultrasound guidance, an 18-ga, spring-loaded
biopsy instrument can provide adequate tissue samples for definitive diagnosis in 83.3% to 96.3% of liver samples.14-16 Perform blood work to evaluate for hemostatic disorders before doing a liver biopsy since abnormalities in platelet counts
and coagulation times increase the likelihood of complications.16 A larger bore needle or a pneumatic instrument can be used to increase the chances of retrieving diagnostic samples. Liver
biopsy samples may be collected with biopsy needles, ligatures, biopsy forceps, a Baker's biopsy punch, or an ultrasonically
activated scalpel by using ultrasound-guided, laparoscopic, and surgical approaches. When determining the appropriate biopsy
method for a patient, consider the suspected underlying disease, concurrent disease processes, anesthetic risks, and potential
for complications such as infection and hemorrhage. In general, all biopsy techniques are associated with minimal hemorrhage
when evaluated in normal dogs.14
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