Introduction

• Most thyroid tumors (~90%) diagnosed pre-mortem are carcinomas:
  • On post-mortem examination up to 50% of thyroid tumors are benign adenomas.
  • Adenomas are consistently small and non-functional.
• Adenomas appear as solid white nodules or cystic structures containing colorless fluid.
• Carcinomas are typically large and irregular with necrotic central areas.
• Carcinomas typically have a tremendous blood supply and hemorrhage readily.
• Signs: typically limited to presence of a ventral cervical mass:
  • Functional adenocarcinoma is rare, signs of hypothyroidism Hypothyroidism.
  • Ectopic thyroid neoplasia can affect tongue base, cranial mediastinum and heart base.
• Diagnosis: radiography, ultrasonography, laboratory tests, cytology or histopathology.
• Clinical stage: CT/MRI, ultrasound, radiography.
• Treatment: surgery, radiotherapy, chemotherapy, possible radio-isotope therapy.
• Prognosis: excellent if complete surgical excision of non-invasive lesion. Up to 6 months if pulmonary metastasis.

Pathogenesis

Etiology

• No inciting cause has been identified for canine thyroid tumors.
• Genetics:
  • In humans there are recognized genetic mutations that predispose to thyroid carcinoma.
  • In dogs there are predisposed breeds from which it can be inferred that there may be an inherited polygenic predisposition.
  • Sporadic reports of multiple endocrine neoplasia; genetic etiology implied.
• Carcinomas can be classified histologically as follicular, solid and medullary:
  • Follicular and solid correspond to thyroxine-producing tissue.
  • Medullary corresponds to parafollicular, calcitonin-producing tissue.
• Most thyroid carcinomas are invasive into local blood vessels, musculature and trachea.
• All carcinomas are histologically malignant but rates of metastasis stated as 38% at diagnosis; up to 80% at death.

Diagnosis

Treatment

Outcomes