Thyroid Flashcards
T3 or T4 more active?
T3 (3-8x more potent)
T3 or T4 longer half life?
T3 more active, T4 longer half life
What are the components of a complete thyroid assessment?
- Serum thyroid hormones (TSH, T3, T4)
- Antibodies
- Thyroglobulin
- Thyroid imaging/scans
- Biopsy (FNA)
What are the indications for free T3/T4 testing?
- Secondary or tertiary hyper/hypothyroidism suspected
- Normal TSH levels despite symptoms of hyper/hypo
What increases TBG?
Pregnancy, OCP, acute infectious hepatitis, biliary cirrhosis
What decreases TBG?
Androgens, glucocorticoids, cirrhosis, hyponatremia, phenytoin, ASA, NSAIDs, nephrotic syndrome.
Which Abs raised in Hashimoto’s?
TgAb
Thyroid peroxidase Abs
TSH receptor inhibiting antibodies
Which Abs raised in Grave’s disease?
Thyroid stimulating immunoglobulin (TSI)
What is the the use of plasma thyroglobulin?
Monitor residual thyroid activity post-thyroidectomy (e.g. for thyroid cancer recurrence - normal/elevated levels suggest persistent, recurrent or metastatic disease)
Normal thyroid size?
15-20g
What is the purpose of thyroid ultrasound?
Measure size of gland, solid v cystic nodule, facilitate FNA biopsy
What is the purpose of radioisotope thyroid scan?
With Technetium-99. Test of STRUCTURE.
- order if nodule and pt is hyperthyroid with low TSH
- Differentiates hot (0% chance malignancy) v cold nodules (5% chance malignancy)
What is radioactive iodine uptake scan?
Test of FUNCTION.
- Order if pt is hyperthyroid
- RAIU measures turnover of iodine by thyroid gland in vivo
- Increased uptake = hyperthyroid
- Decreased uptake = gland leaking (thyroiditis); exogenous thyroid hormone intake
Indications for thyroidectomy?
- Malignancy
- Symptomatic goitre
- Medically refractory hyperthyroidism (i.e. Graves)
Thyroidectomy contraindications?
- Uncontrolled Graves (concerns re thyroid storm)
- Pregnancy (postpone surgery IF possible: ind in aggressive ca or airway compromise)
Thyroid embyrology?
Develops from D24.
Arises from endodermal epithelial cells on median surface of pharyngeal floor (foramen caecum).
Descends W7 anterior to hyoid / cricoid to rest anterior to trachea.
What is the pyramidal lobe of the thyroid?
Descent of thyroid marked by thyroglossal duct (tubular structure of thyroid tissue). Usually obliterates W7-10. Persistence of inferior aspect = thyroglossal duct.
Components of thyroid gland?
2 lateral lobes and central isthmus (+/- pyramidal lobe).
Which layer is the thyroid located in?
Middle layer of deep cervical fascia
What does the middle layer of the deep cervical fascia envelop?
- Strap muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles).
- Pharynx, larynx, trachea, esophagus, thyroid, parathyroids, buccinators, and constrictor muscles of the pharynx.
What attaches the thyroid to the thyroid and cricoid cartilages?
Anterior suspensory ligament
What is Berry’s ligament?
Posterior suspensory ligament. Attaches thyroid first and second tracheal ring, and the cricoid cartilage.
What covers the thyroid anteriorly?
Sternohyoid and sternothyroid muscles.
Arterial supply to thyroid?
- Superior thyroid artery (off external carotid artery)
- Inferior thyroid artery (off thyrocervical trunk)
Venous drainage of thyroid?
Superior / middle / inferior thyroid veins.
Join internal jugular or innominate veins.
Which lymph nodes drain the thyroid?
Prelaryngeal, pretracheal, paratracheal and supraclavicular nodes.
Possible locations for parathyroid glands?
Anterior or posterior mediastinum, carotid bifurcation, retro-oesophageal, retropharyngeal or retrolaryngeal regions.
Vascular supply to parathyroids?
Inferior thyroid artery
Complications of thyroidectomy?
- Hypocalcemia 2” to hypoparathyroidism
- Injury to recurrent laryngeal nerve / superior laryngeal nerve
- Neck haematoma
- Infection
- Thyroid storm
Vertebral location of thyroid?
C5 - T1
