Anatomy of the thyroid gland

Position of the thyroid gland:

• Infront of the neck
• In the midline
• Infront of the trachea
• Extends up to the thyroid cartilage

Parts of the thyroid gland:

• 2 lobes
• Connected by an isthmus
• infront of the 2nd & 3rd tracheal ring
• Pyramidal lobe
• left end of isthmus

Capsules:

• True capsule (thickening of the connecting tissue)
• False capsule (pretracheal fascia)

Important relations:

Anterior:

Strap muscles

• strenohyoid muscle
• sternothyroid muscle

In surgery, retracting these muscles will expose the thyroid gland

Posterior:

• trachea
• enlargement of thyroid gland can compress trachea and cause difficulty in breathing
• oesophagus

Posterolateral:

• Carotid artery
• Internal jugular vein

Embedded inside the gland:

• 2 pairs of parathyroid gland

Nerves:

Recurrent laryngeal nerve

• Runs in the tracheoesophageal groove
• Passes in between the branches of the inferior thyroid artery
• During surgery, inferior thyroid artery will be clamped. RLN can be accidentally damaged as well.
• 1 side damage: Husky voice
• Both side damage: No voice & Stridor

Venous drainage

• Superior thyroid vein
• drains into internal jugular vein
• Middle thyroid vein
• drains into internal jugular vein
• Inferior thyroid vein
• drains into brachiocephalic vein

Lymphatic drainage

• Pretracheal lymph node
• Paratracheal lymph node
• Deep cervical lymph node

Papillary carcinoma spread thru lymph node

Microscopic arrangement of the thyroid gland

• Arranged as follicles
• lined by cuboidal epithelium
• cells secrete thyroxine
• binds to globulin & stored as thyroglobulin (colloid)
• in between follicles
• parafollicular cells (secrete calcitonin)
• medullary carcinoma arise from here

Development of thyroid gland (embryology)

Migration of thyroid:

Thyroid gland develops as an outgrowth from the foetal pharynx & decends to the neck region.

 

Abnormalities:

• Thyroglossal fistula
• a tract can persist
• Throglossal cyst
• part of the tract can persist
• Ectopic thyroid
• thyroid tissue remain along the tract