ISSN 2398-2969      

Thyroid gland: neoplasia

icanis
Contributor(s):

Gerry Polton


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

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pack L, Roberts R E, Dawson S D & Dookwah H D (2001) Definitive radiation therapy for infiltrative thyroid carcinoma in dogs. Vet Radiology & Ultrasound 42 (5), 471-4 PubMed.
  • Théon A P, Marks S L, Feldman E S & Griffey S (2000) Prognostic factors and patterns of treatment failure in dogs with unresectable differentiated thyroid carcinomas treated with megavoltage irradiation. JAVMA 216 (11), 1775-1779 PubMed.
  • Brearley M J, Hayes A M & Murphy S (1999) Hypofractionated radiation therapy for invasive thyroid carcinoma in dogs - a retrospective analysis of survival. JSAP 40 (5), 206-210 PubMed.
  • Klein M K, Powers B E, Withrow S J et al (1995) Treatment of thyroid carcinoma in dogs by surgical resection alone: 20 cases (1981-1989). JAVMA 206 (7), 1007-1009 PubMed.

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