Thyroid Flashcards
(37 cards)
Embryology of thyroid
Develops from foramen cecum (base of tongue)
Descends to anterior neck forming thyroglossal duct
Position of the thyroid
Wrapped around cricoid cartilage and superior rings of trachea C5-T1
Within visceral compartment of the neck, surrounded by pre-tracheal fascia
Two lobes
Position of the thyroid
Tow lobes
Overlying cricoid cartilage and superior rings of trachea
C5-T1
Visceral compartment of neck, bound by pretracheal fascia
Blood supply to thyroid
Superior thyroid artery (1st branch of external carotid)
Inferior thyroid artery (thyrocervical trunk, branch of subclavian)
Thyroid ima artery (in 10%, from brachiocephalic trunk)
Venous drainage of the thyroid
Venous plexus Drains into Superior thyroid vein (drains into IJV) Middle thyroid vein (drains into IJV) Inferior thyroid vein (brachiocephalic)
Lymphatic drainage of thyroid
Paratracheal nodes
Deep cervical nodes
Innervation of the thyroid
Sympathetic trunk
Anatomical relations of the thyroid
Right & left recurrent laryngeal nerves run through tracheoesophageal groove passing deep to thyroid to innervate larynx
Type of thyroid cells
Follicular cells: thyroid epithelium: simple cuboidal. Form follicles filled with colloid.
Parafollicular cells.
Function of the thyroid
Endocrine gland
Produces: T3/T4 and calcitonin
Hypothalamic-pituitary-thyroid axis
Hypothalamus detects low T3/T4 conc and releases thyrotrophin-releasing hormone (TRH) into hypophyseal portal system
TRH binds to receptors on thyrotrophic cells of ant pituitary causing them to release TSH
TSH binds to receptors on basolateral membrane of thyroid and induces synthesis and release of thyroid hormone from follicular cells
Functions of follicular cells
Effects of T3/T4
increases BMR Gluconeogenesis Glycogenolysis Lipogenesis Thermogenesis Increases expression of B receptors of cardiac tissue
Functions of parafollicular cells
Produce calcitonin
Effects of calcitonin
Inhibits Osteoclasts, reducing bone resorption
Inhibits renal tubular reabsorption of calcium and phosphate
Opposes effect of PTH
Net effect: reducing Ca2+
Thyroid cancer subtypes
Papillary carcinoma (75%) Follicular carcinoma (15%) Medullary carcinoma (3%) Anaplastic thyroid cancer (5%) Lymphoma (1-2%)
Papillary Carcinoma
Most common (75%). Most commonly 40-50 women. RFs: ionising radiation in childhood
Multiple lesions within gland. Rarely encapsulated.
Histology: papillary and colloid-filled follicles. “Orphan Annie Eye nucleus” (little protein/DNA).
Commonly spread to lymphatics
Good prognosis: 90% 10 year survival
Follicular carcinoma
2nd most common (15%). Usually seen 40-60 women. RF: low dietary iodine.
Focal encapsulated lesions.
Invades blood vessels.
Mets: maematogenous spread: Lungs, liver, bone, brain. Unlikely to invade lymph node.
Subtype: Hurthle cell tumours.
Medullary carcinoma
Rare (3%). RF: MEN2a/2b
From parafollicular cells (more commonly found in superior 1/3).
Histology: spindle shaped cells with amyloids
Raised calcitonin levels. Can secrete VIP/serotonin.
Lymphatic and medullary spread.
Poor prognosis.
Anaplastic thyroid cancer
5%. RFs: elderly
Aggressive: Rapidly growing with early local invasion.
Poor prognosis.
Signs of thyroid cancer
Single hard thyroid nodule.
Local invasion: hoarseness (larynx/RLN), dysphagia (oesophagus).
Usually non-functional (no Sx of hyper/hypothyroid).
Investigation of thyroid cancer
Initial TFTs. Calcitonin
US neck (micro calcifications, hypoechongenicity, irregular margin)
Fine needle aspiration cytology.
Management of thyroid cancer
Surg: Hemi-thyroidectomy, total thyroidectomy +/- neck dissection
Non-surg: radioiodine, external beam radiotherapy, chemo.
Parathyroid glands location
Posterior aspect of the thyroid gland
External to thyroid
Contained within pretracheal fascia
