Hepatic neuroendocrine tumor
Neuroendocrine cells, which produce peptides and amines, are distributed in many organs and tissues. The most common sites are the respiratory and digestive tracts. In the past, these cells were called 'APUD' (amine precursor uptake and decarboxylation) cells. They were thought to be neuroectodermal in origin, arising from the neural crest. At present, these neuroendocrine cells, especially the epithelial-associated cells, are considered to be endodermal in origin and are designated as diffuse endocrine system.
Hepatic neuroendocrine tumors arise from the diffuse neuroendocrine system and range in clinical appearance from benign carcinoids to the aggressive neuroendocrine carcinoma (Merkel cell carcinoma).
In dogs, primaru neuroendocrine tumors can arise in sites such as the intestines, esophagus, nasal cavity, skin, bile duct, gallbladder, liver, and nasopharynx. Peritoneal carcinomatosis and metastasis to regional lymph nodes occurs frequently.
Hematological analysis often shows leucocytosis, elevated ALT, ALP, hyperalbuminemia and increased albumin/globulin ratio. Prothrombin and activated prothrombin times should also be evaluated to asses clotting function.
A definitive diagnosis requires histopathological examination of biopsied tissue. These tumors stain positively with Grimelius silver as well as the immunohistochemical markers synaptophysin, neuron-specific enolase and chromagranin-A.
A differential diagnosis would include hepatic adenoma, cholecystitis, hepatitis, hepatic carcinoma, bile duct carcinoma, liver flukes (especially Clonorchis sinensis), hepatic adenoma and secondary metastatic lymphoma.
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