BACKGROUND: Carcinoid is a neoplasm of neuroendocrine cells that mostly originates in the gastrointestinal and pulmonary systems, and so far, there have been sporadic cases of its primary type in the liver of animals.
OBJECTIVES: Only sporadic reports have been published on primary hepatic involvement by neuroendocrine tumors in dogs, and these neoplasms can be challenging to distinguish from more common hepatic tumors such as hepatocellular carcinoma. Accurate diagnosis relies on a combination of distinctive histomorphologic features and specific immunohistochemical markers like synaptophysin, which aids in differentiating neuroendocrine tumors from other hepatic malignancies.
METHODS: Two dogs were referred to the Veterinary Hospital, Faculty of Veterinary Medicine, University of Tehran. Case 1 was a 9-year-old spayed female Terrier presented with two large hepatic masses detected by ultrasonography and CT scan. Case 2 was a 13-year-old male dog with a history of recurrent vomiting and a single hepatic mass identified on abdominal ultrasonography. Following surgical resection, the specimens were fixed in 10% neutral buffered formalin, routinely processed, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Immunohistochemistry with anti-synaptophysin antibody was performed for confirmation.
RESULTS: In Case 1, ultrasonography and CT scan revealed two well-demarcated hyperechoic and heterogeneous hepatic masses. Histologically, the neoplastic tissue consisted of uniform round to polygonal cells arranged in rosette-like, nested, and ribbon-like patterns within a delicate fibrovascular stroma with minimal stromal reaction and a low mitotic count (2/10 HPFs). In Case 2, a well-circumscribed hepatic mass measuring approximately 5 × 3 cm was identified. Histopathology showed similar carcinoid architectural patterns, but with a higher mitotic count (15/10 HPFs), vascular invasion, and hepatic lymph node metastasis. Both cases demonstrated strong cytoplasmic immunoreactivity for synaptophysin, confirming the diagnosis of primary hepatic neuroendocrine tumor (carcinoid).
CONCLUSIONS: This report presents a rare case of primary neuroendocrine tumor of the liver in two dogs. The minimal stromal reaction observed further supports the neuroendocrine nature of the tumor. This case highlights the importance of integrating histopathology and immunohistochemistry for precise diagnosis, which is critical for prognosis and treatment planning in veterinary oncology.