4. Endemic and sporadic goiter

DEFINITION

• Goitre is enlargement of the thyroid gland, with or without altered thyroid function.
• It may be diffuse or nodular, toxic or non-toxic.
• Endemic goitre traditionally refers to increased prevalence in a population due to iodine deficiency; sporadic goitre occurs without a population-level iodine deficiency and may relate to dyshormonogenesis, goitrogen exposure, autoimmune disease or nodular transformation.
• Goitre is a clinical finding, not a final diagnosis.

THYROID ANATOMY AND PHYSIOLOGY

• The thyroid has two lobes joined by an isthmus, usually lying anterior to the upper trachea.
• It is supplied by superior and inferior thyroid arteries; venous drainage is via superior, middle and inferior thyroid veins.
• The recurrent laryngeal nerves and parathyroid glands are surgically important.
• Follicular cells produce T4 and T3 under TSH stimulation; parafollicular C cells produce calcitonin.
• Iodine is required for thyroid hormone synthesis.
• The hypothalamic-pituitary-thyroid axis regulates secretion by negative feedback.

AETIOLOGY AND CLASSIFICATION

• Causes include iodine deficiency, autoimmune thyroiditis, Graves disease, multinodular goitre, solitary nodules, congenital hormone synthesis defects, pregnancy-related physiological enlargement, drugs such as lithium or amiodarone, and rarely malignancy.
• Classify by diffuse/nodular, simple/toxic, substernal/cervical, and WHO palpation/size grade where relevant.
• Multinodular goitre develops through repeated cycles of follicular hyperplasia and involution, producing nodules, cystic degeneration, haemorrhage and calcification.