Hepatic Neoplasia

• Primary hepatic tumours are rare (less than 1.5% of all canine tumours and 1.0-2.9% of all feline tumours) * However, the liver is a common site of metastatic tumours due to the rich blood supply (hapatic portal vein and hepatic artery)
• In dogs, metastasis to the liver is 2.5 times more likely than primary neoplasia
• In cats, primary hepatobillary tumours are more frequent than metastatic tumours
• Malignant tumours are more common in dogs
• Benign tumours are more common in cats
• Malignant primary tumours include:
  • Hepatocellular carcinoma
  • Cholangiocellular carcinoma
  • Gall bladder carcinoma
  • Haemangiosarcoma
  • Mast cell tumour
  • Hepatic carcinoids (neuroendocrine)
• Benign tumours include:
  • Hepatocellular adenoma (hepatoma)
  • Cholangiocellular adenoma
  • Gall bladder adenoma

Note: Distinction must be made between all hepatic tumours and benign nodular hyperplasia that is frequently observed in the older canine. The most significant primary tumours in the dog are hepatomas, hepatocellular and cholangiocellular carcinomas and hepatic carcinoids. Hepatocellular carcinomas and cholangiocellular carcinomas are the most significant in cats.

Diagnosis

Symptomatic in approximately 75% of dogs and 50% of cats, particularly if malignant.

Clinical signs

• Usually non-specific:
  • Weight loss
  • Inappetance
  • Lethargy
  • Polyuria-Polydipsia
  • Vomiting
  • Ascites
• Neurological Signs - seizures, ataxia and weakness occur less frequently. They may be due to metastasis to the central nervous system, hepatic encephalopathy or hypglycaemia which can occur as a paraneoplastic syndrome
• Icterus - Particularly in dogs with extrahepatic cholangiocellular carcinomas and diffuse carcinoids

Physical Examination

• Cranial abdominal mass - palpable in up to 75% of cats and dogs

Haematology and Biochemistry

• Usually non-specific. The following are frequently observed in dogs:
  • Mild non-regenerative anaemia - cause idiopathic, however anaemia of chronic disease, inflammation, red blood cell sequestration and iron deficiency may play roles
  • Leukocytosis - resulting from the associated inflammation and necrosis that can occur with large liver masses
  • Thrombocytosis - potential causes include production of thrombopoietin as a parneoplastic syndrome, iron deficiency, inflammatory cytokines and anaemia
• Elevated hepatic enzymes - likely due to hepatocellular damage or biliary stasis though the extent of enzyme increase is not proportional to severity of liver damage
• Hypoalbuminaemia
• Hyperglobulinaemia
• Hypoglycaemia - can occur as a paraneoplastic syndrome where there is increased utilisation of glucose or increased production of hormones with insulin-like activity.
• Elevated pre- and postprandial bile acids

• The following have been observed in cats:
  • Azotaemia
  • Elevated hepatic enzymes
  • Elevated serum bilirubin - particularly in those with hepatocellular carcinoma

Plain Abdominal Radiography

Hepatomegaly and rounding of the margins of the liver may be observed. Alternatively a cranial abdominal mass may be visible with displacement of the stomach caudally and laterally with massive hepatic neoplasms. Occasionally mineralisation of the biliary tree is observed in dogs with cholangiocellular carcinoma. Three thoracic views should also be taken to assess lung metastasis although this is uncommon at the time of diagnosis.

Ultrasonography

Advised to evaluate the condition of surrounding structures. It also allows classification of the mass as massive, nodular or diffuse. Doppler techniques can also be utilised to assess the vascular structure of tumours. Guided fine-needle aspirates or core biopsies can also be taken at this time (a coagulation profile is highly recommended prior to performing a liver biopsy due to risk of haemorrhage). If the lesion is solitary and massive surgical resection without preoperative biopsy is usually undertaken as diagnosis and treatemnt are accomplished in one procedure.

Advanced Imaging

CT and MRI are more sensitive in detecting small lesions and confirming the relationship of the mass with surrounding tissues and vasculature.

Abdominocentesis

Cytological examination of the sediment may reveal neoplastic cells. Effusions are usually modified transudates and haemorrhage may indicate tumour rupture.

Signalment and Description

Hepatocellular Tumours (Hepatocellular carcinomas (HCC) and Hepatomas)

• HCC occurs more frequently in dogs and hepatomas more commonly in cats. They are the most common primary liver tumour in dogs and the second most common in cats.
• Male dogs over 10 years old are the most frequently affected by HCC and Miniature schnauzers may have a breed predisposition.
• Regional lymph nodes (hepatic and diaphragmatic nodes), peritoneum and lungs are the most frequent sites of metastasis in dogs with nodular and diffuse HCC.
• Metastatic rate for dogs with massive HCC: 0-37%
• Metastatic rate for dogs with nodular and diffuse HCC: 93-100%
• Hepatomas are usually incidental findings and non-significant

Cholangiocellular Tumours (Bile duct carcinomas and adenomas)

• Bile duct carcinomas are the most common malignant hepatobillary tumours in cats and the second most frequent in dogs and females may be predisposed
• Intrahepatic carcinomas are more frequent in dogs. In cats there have been reports of both equal occurrence of intra-and extrahepatic tumours and of a extrahepatic dominance.
• Bile duct carcinomas are aggressive with metastasis to particularly the regional lymph nodes and lungs frequently being observed in dogs and diffuse intraperitoneal metastasis and carcinomatosis being common in cats.
• Bile duct adenomas (also known as biliary or hepatobiliary cystadenomas) are common in cats, particularly males.
• Bile duct adenomas are non-significant unless they of sufficient size to compress surrounding soft tissue structures

Carcinoids (Neuroendocrine Tumours)

• Usually occur in younger animals compared with other primary hepatobiliary tumours.
• Primary tumours are aggressive and often affect more than one liver lobe and metastasise most frequently to the regional lymph nodes, the lungs and peritoneum.

Sarcomas (Haemangiosarcoma (HSA), Leiomyosarcoma, Fibrosarcoma)

• HSA is the most common hepatic sarcoma in cats
• Leiomyosarcoma is the most common hepatic sarcoma in dogs
• These tumours are aggressive and metastasis to the spleen and lungs is frequently observed.

Treatment

Surgery

Surgical excision is adivsed for hepatic adenomas, bile duct adenomas and massive hepatocellular carcinomas. Nodulectomy or lobectomy can be used for focal tumours of one or more lobes. Diffuse tumours and widespread nodular disease carry a worse prognosis.

Chemotherpay

Not currently recommended for primary hepatic neoplasia. Some metastatic sarcomas, for example haemangiosarcomas, may show some response.

Radiotherapy

Not reported. Surrounding abdominal organs may show poor tolerance.

Prognosis

The mean survival time for massive hepatocellular cacinomas following surgery is approximately 1 year. Otherwise the prognosis is poor for other malignant and metastatic tumours. If successfully excised the prognosis for benign tumours is good.

References

• Morris J, Dobson J (2001) Gastrointestinal Tract, in Small Animal Oncology, Blackwell Science, pp 137-140
• Withrow S.J, Vail D.M (2007), Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, fourth edition, Missouri, Saunders Elsevier, pp 483-489