Hepatocellular adenoma in dogs, also referred to as "hepatoma," is a benign tumor originating in the liver. It is commonly found in senior dogs over the age of ten. This type of tumor tends to invade the cells that line the surfaces of the body (epithelial cells). Although categorized as benign, this tumor has the potential to rupture causing anemia and weakness in affected dogs. Removal of the tumor is the standard practice considering the risks for rupture, and the aggravating factor, that, on x-rays or ultrasound, this tumor may be challenging to differentiate from hepatocellular carcinoma, the malignant version.
Hepatocellular Adenoma in Dogs
Hepatocellular adenoma is a benign tumor of epithelial origin. The word "hepato" derives from the Greek word for liver, while the word "cellular"indicates that this is a cancer affecting the cells, in this case, the epithelial cells known to line the surface of the liver.
The term "adenoma," on the other hand, indicates a benign tumor that forms from glandular structures in epithelial tissue.
Affected dogs are typically over the age of 10 and no particular dog breeds appear to be predisposed. Dogs with this type of tumor may not exhibit specific symptoms, but when they do, the signs tend to be quite vague and non-specific.
Signs may include lethargy, loss of appetite, vomiting, diarrhea, increased drinking, increased urination and abdominal distension and pain. Several of these signs are often seen when the tumor grows large and ends up pressing on the stomach.
How large is too large though? Generally, if the mass is found only on one lobe, since dogs are equipped with 6 liver lobes, this tells us that it is not very large and only takes up at least 16 percent of the liver, explains veterinarian Dr. B.
However, regardless of size and the fact of being benign, hepatocellular adenomas in dogs may end up acutely rupturing which leads to potentially life-threatening leakage of blood in the peritoneal cavity (the space within the abdomen that contains the intestines, the stomach, and the liver) with its associated weakness and shock-like symptoms (pale gums, rapid pulse, rapid breathing, dizziness).
Diagnosis of Canine Hepatocellular Adenoma
Many dogs are found to have this tumor by accident, in other words, they are seen for something else, and the finding is incidental.
Blood work may reveal a regenerative anemia if there is recent bleeding from the mass or there can be non-regenerative anemia as seen in anemia of chronic disease.
Other bloodwork abnormalities may include increased white blood cell count and mild to markedly high levels of liver enzymes (ALP, ALT, AST).
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The tumor can be detected on x-rays (a mass may be seen altering the liver's normal silhouette) and ultrasound (a solitary mass or multiple masses are found), but solely based on these imaging techniques, it can be challenging to differentiate from hepatocellular carcinoma (the malignant version), hepatic nodular hyperplasia and hepatic abscesses. A CT scan may provide additional information by detecting additional lesions.
Fine needle biopsy done during an ultrasound may not be very insightful. It is reported to be only 33.3 percent percent accurate when performed on masses on the liver, which is much lower compared to other anatomical sites. It can certainly help identify atypical cells, but won't provide a definite answer as to whether the tumor is benign or low-grade malignant. However, this test may prove to be somewhat helpful in excluding certain types of cancers such as lymphomas.
Definite diagnosis of hepatocellular adenoma in dogs is obtained only by exploratory surgery accompanied by removal of the mass along with the lobe (liver lobectomy) which is then submitted to histopathology for microscopic examination and diagnosis.
Generally, hepatocellular adenomas in dogs present as single, well-circumscribed, roundish nodules that are less than 10 centimeters in diameter but occasionally may be found to be over 20 centimeters. The nodules are usually yellow-brown in color, quite vascular and friable which makes them prone to rupturing.
Treatment of Hepatocellular Adenoma
Surgical removal is the treatment of choice especially with masses that are large, cause symptoms or impact organ function. A CT scan conducted prior to surgery helps provide important pre-surgical information about the surgery's feasibility.
Adenomas that rupture and bleed require emergency care so to prevent shock and to stabilize the dog preventing him from bleeding out. Blood transfusions may be needed to restore excessive blood loss.
Emergency exploratory surgery performed by an experienced surgeon is typically performed without major consequences to the liver. The good news is that the liver is capable of regenerating itself, and with removal of large masses in healthy dogs provided with supportive care, it is expected to regenerate fairly quickly (generally within 6 to 8 weeks). Failure to perform surgery may lead to massive abdominal hemorrhage.
Interestingly, the size of the tumor is not a negative prognostic factor considering that up to 75 percent of the liver can be surgically removed with no significant impact on the liver's overall functionality. Dogs presenting with large solitary liver tumors that turn out being hepatocellular adenomas therefore usually have a good prognosis after surgery which is ultimately considered curative.
For further reading:
- Dog liver cancer biopsy procedure and costs
- Life expectancy of dogs with hepatocellular carcinoma
- Causes of enlarged liver in dogs
- How steroids affect the dog's liver
- Dog cancer spread to the liver
- Life expectancy in dogs with liver cancer
- Drugs toxic to dog's liver
- Blackwell's Five-Minute Veterinary Consult: Canine and Feline, edited by Larry P. Tilley, Francis W. K. Smith, Jr.
- Magne ML, Withrow SJ. Hepatic neoplasia. Vet Clin North Am Small Anim Pract. 1985;15:243–256
- Thamm DH. Hepatobiliary tumors. In: Withrow SJ, MacEwen EG, eds. Small Animal Clinical Oncology, 3rd ed. Philadelphia: WB Saunders, 2001:327–334