Embryology & surgical anatomyThe 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.

The normal parathyroid gland weighs up to 50 mg with a characteristic orange/brownColour & mobility within the surrounding fat & thymic tissue.

Most adults have four parathyroid glands.

The superior parathyroid is more consistent in position than the inferior.

physiologyThyroxine. 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 .

Thyroglossal cyst

Thyroglossal fistula

Hypothyroidism

Classification:

Autoimmune thyroiditis non-goitrous goitrous

Iatrogenic after thyroidectomy or radioiodine therapy drug induced.

DyshormonogenesisGoitrogens

Secondary to hypothalamic or pituitary diseaseThyroid agenesisEndemic cretinism

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

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.

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

adenomaNeoplastic benign

malignant

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

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 .

Goitre,retrosternal

Goitre,retrosternal

FNAC

FNAC

FNAC