Adenocarcinoma originating from presumed liver ectopic thyroid in a cat

Area of Science:

• Veterinary Pathology
• Comparative Oncology
• Feline Medicine

Background:

• Ectopic thyroid tissue is uncommon in domestic animals, with rare reports in dogs and cats, typically in prediaphragmatic locations.
• Hepatic tumors in cats are often of non-thyroid origin, making ectopic thyroid tissue a rare consideration.

Observation:

• A 15-year-old domestic shorthair cat presented with a liver nodule diagnosed via ultrasound and fine-needle aspiration as carcinoma.
• Staging via CT scan ruled out primary thyroid tumors or distant metastases.
• Surgical resection (hepatic lobectomy) and histological examination confirmed thyroid adenocarcinoma arising from ectopic tissue within the liver.

Findings:

• Histopathology and immunohistochemistry (thyroglobulin staining) confirmed the diagnosis of thyroid adenocarcinoma.
• The tumor was definitively identified as originating from ectopic thyroid tissue within the liver, with no evidence of primary thyroid neoplasia.
• The cat experienced an uncomplicated surgical recovery.

Implications:

• This case represents the first documented instance of thyroid adenocarcinoma arising from ectopic thyroid tissue within the liver of a cat.
• Highlights the importance of considering ectopic thyroid tissue in the differential diagnosis of feline liver masses, even in unusual locations.
• Contributes to the understanding of rare tumor origins and locations in veterinary oncology.