2. Embryology & surgical anatomy The thyroglossal duct develops from the median bud of the pharynx. The foramen caecum at the base of the tongue is the vestigial remnant of the duct. The parathyroid glands develop from the third & fourth pharyngeal pouches. The parafollicular cells( C cells ) from the neural crest. The normal thyroid gland weighs 20-25 g. The functioning unit is the lobule supplied by single arteriole & consisting of 24-40 follicles lined with cuboidal epithelium. The follicle contains colloid in which thyroglobulin is stored. The arterial supply is rich & anastomoses occur between the main thyroid arteries & branches of the tracheal & oesophageal arteries. There is an extensive lymphatic network within the gland. The subcapsular plexus drains principally to the central compartment juxtathyroid nodes, paratracheal nodes & nodes on the superior & inferior thyroid veins & from there to the deep cervical & mediastinal groups of nodes.

3. The normal parathyroid gland weighs up to 50 mg with a characteristic orange/brown Colour & mobility within the surrounding fat & thymic tissue. Most adults have four parathyroid glands. The superior parathyroid is more consistent in position than the inferior.

4. physiology Thyroxine. T3 & T4 are bound to thyroglobulin within the colloid. In the serum, they are bound to serum proteins: albumin, TBG & TBPA. The small amount of hormone that remains free in the serum is biologically active. T3 is quick acting( within a few hours ), whereas T4 acts more slowly( 4-14 days ). Parathyroid hormone (PTH) secreted by the parathyroid gland, controls the level of serum calcium & extracellular fluid. Calcitonin is secreted by parafollicular C-cells, it is a serum marker for recurrence of medullary thyroid cancer.

5. Thyroglossal cyst

6. Thyroglossal fistula

7. Hypothyroidism Classification : Autoimmune thyroiditis non-goitrous goitrous Iatrogenic after thyroidectomy or radioiodine therapy drug induced. Dyshormonogenesis Goitrogens Secondary to hypothalamic or pituitary disease Thyroid agenesis Endemic cretinism

8. Fetal or infantile hypothyroidism CRETINISM. Adult hypothyroidism: signs : bradycardia cold extremities dry skin & hair periorbital puffiness hoarse voice symptoms : tiredness mental lethargy cold intolerance weight gain constipation menstrual disturbance carpal tunnel syndrome

9. Thyroid function tests show low T4 & T3 levels with a high TSH. High serum levels of TPO antibodies are characteristic of autoimmune disease. Treatment : oral thyroxine 0.10-0.20mg as a single daily dose.

10. Thyroid enlargement The term goitre is used to describe generalised enlargement of the thyroid gland. Solitary or isolated swelling(nodule): a discrete swelling in one lobe with no palpable abnormality elsewhere. 70% Dominant nodule: discrete swelling with evidence of abnormality elsewhere. 30% Classification of thyroid swelling: Simple goitre – diffuse hyperplastic: physiological, pubertal, pregnancy. multinodular goitre. Toxic diffuse: Graves’ disease multinodular adenoma Neoplastic benign malignant

11. Inflammatory Autoimmune : chronic lymphocytic thyroiditis Hashimoto’s thyroiditis Granulomatous :De Quervain’s thyroiditis Fibrosing : Reidel’s thyroiditis Infective: acute – bacterial, viral chronic – TB, syphilis Other Amyloid

12. Thyroid nodules Are present in 3-4% of adult population in the UK & USA. Are three to four times more frequent in women than men. Diagnosis: the importance of thyroid nodules lies in the increased risk of neoplasia. 15% of isolated swellings prove to be malignant. 30-40% are follicular adenoma. remainder are non neoplastic. Investigations : Thyroid function. Autoantibody titres. Isotope scan. 80% are cold nodules but only 15% prove to be malignant. Ultrasonography. FNAC. CXR. CT & MRI. Laryngoscopy. Core biopsy.

13. Goitre,retrosternal

15. FNAC