Liver disease is common in dogs and liver tumors are one of many potential causes of canine liver disease. Liver tumors in dogs occur in many different forms. Canine hepatic tumors may be primary tumors, derived from the liver itself, or they may be metastatic, derived from another body tissue and spread to the liver from that tissue. Liver tumors may be malignant (cancerous) or benign (non-cancerous). Canine liver tumors can also take on different shapes, including:
- massive - a solitary localized lesion within the liver
- diffuse - affecting the entire area of the liver in an even distribution pattern
- nodular - numerous discreet lesions located within the liver
Types of Canine Liver Tumors
The most common types of liver tumors seen in dogs are:
- hepatocellular carcinoma (malignant)
- hepatocellular adenoma (usually benign)
- hepatoblastoma (rare)
- biliary carcinoma (malignant)
- biliary adenoma (benign)
- neuroendocrine (carcinoid) tumors (rare)
- hemangiosarcoma (a malignancy of blood vessels, a common secondary tumor)
- fibrosarcoma (a malignancy of fibrous tissue)
- osteosarcoma (a bone malignancy)
- leiomyosarcoma (a smooth muscle malignancy)
Primary Versus Metastatic Liver Cancer in Dogs
Liver tumors can be primary or metastatic. Malignant liver cancer is more likely to be metastatic than primary and the most common tissues of origin are:
- the pancreas
- the intestinal tract
- the spleen
Metastasis indicates that the cancer has already had the opportunity to spread and, therefore, in most cases, the prognosis with metastatic cancer is poor because the cancer is already advanced.
The prognosis for primary liver tumors depends on the type of tumor involved, whether the tumor is benign or malignant, and whether the lesion is massive, diffuse or nodular. Benign tumors carry a much better prognosis than do malignant cancers of the liver.
Massive liver tumors are more likely to be amenable to surgical correction than are diffuse or nodular tumors.
Diagnosis of Liver Disease in the Dog
Diagnosing liver disease of any type involves blood testing, including complete blood counts and blood chemistry profiles. Liver disease may cause changes in the red blood cell counts if there are clotting deficits present or if the dog is anemic. Blood chemistry profiles may reveal elevations in liver enzymes such as ALT (alanine aminotransferase) or ALP (alkaline phosphatase), elevations in bilirubin levels and decreases in the blood urea nitrogen. Blood protein levels may be altered as may electrolyte levels, depending on the individual dog's symptoms. Other blood tests that are often used to evaluate liver function include bile acids and sometimes ammonia levels.
Radiographs of the abdomen can reveal changes in the overall size and shape of the liver and may give valuable clues that the liver is diseased. However, abdominal ultrasound allows more accurate evaluation of the texture of the liver. Abdominal ultrasound can be used to determine where liver tumors are located, how many tumors are visible, how much normal liver tissue is left, whether local lymph nodes appear normal and whether surgical resection of a tumor is likely to be useful.
Specific Diagnosis of the Type of Canine Liver Tumor or Liver Cancer
Actual diagnosis of the type of tumor invading the liver will likely involve a needle aspirate or a biopsy of the abnormal liver tissue. A needle aspirate involves collecting cells from the abnormal liver tissue to be examined microscopically. The needle aspirate is often performed using ultrasonic guidance and is minimally invasive but may yield less specific results than a liver biopsy.
A liver biopsy involves collecting a piece of liver tissue for microscopic examination. With a liver biopsy, the architecture of the specimen is retained and diagnosis is often more specific and more reliable than a needle aspirate sample. However, a liver biopsy is a more invasive test than a needle aspirate and results may take longer to obtain because the sample preparation is more extensive. The risks of complications with a liver biopsy are higher than those of a needle aspirate and include abnormal bleeding due to clotting deficits.
The diagnosis of a liver tumor in a dog can involve many different variables, including whether the tumor is benign or malignant, whether the lesion is primary or metastatic, what specific type of tumor or cancer is involved and how the lesion or lesions are distributed within the liver. Prognosis ranges from good for benign localized liver tumors to very guarded or poor with malignant and/or metastatic cancers of a diffuse or nodular nature.
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