These tumors are usually slow-growing masses which are commonly diagnosed as an incidental finding on ultrasonography or at postortem and rarely cause clinical disease.
Hepatic adenoma are characterized by a characteristic well-circumscribed and demarcated growth similar to nodular hyperplasia and can grow quite large. They are usually single, may be quite large (up to 20 cm) and often exhibit a pedunculated attachment.
These tumours occur with a higher frequency than the malignant counterpart, and usually occur in dogs over 10 years of age.
Adenomas consist of a friable, highly vascular parenchyma, and rupture with subsequent haemoperitoneum may be the clinical presentation.
These tumors rarely causes physical symptoms until the interfere with normal hepatic function and may then cause abdominal distension, ascites, lethargy, anorexia and weight loss.
Diagnosis is usually achieved with radiographic or ultrasonographic imaging. With ultrasonography, these tumors may exhibit malignant contrast-enhanced characteristics and results should be interpreted cautiously. A fine-needle biopsy should be interpreted histologically for evidence of adenocarcinomatous changes.
Histologically, these tumours may be difficult to distinguish from nodular hyperplasia or even normal liver tissue. Histologically, encapsulation and compression of adjacent hepatic parenchyma are characteristic features. Immunohistochemical staining with cytokeratin and hepatocyte paraffin 1 may help achieve a definitive diagnosis.
A differential diagnosis includes biliary cystadenoma, hepatic carcinoma, hepatic lymphoma, hepatitis, nodular hyperplasia, vacuolar change, fibrosis, metastatic neoplasia, necrosis, hepatic lipidosis, round cell tumour, steroid hepatopathy, extramedullary haematopoiesis and secondary metastases (e.g. hemangiosarcoma).
Complete surgical resection is curative but by the time of diagnosis high tumour burden may make this unachievable. Chemotherapy may be the only option in the treatment of unresectable hepatocellular adenoma, using doxorubicin.
The prognosis for respectable hepatocellular adenomas is good, and survival times of up to 2 years have been reported.
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