MEDI7302 Study Guide - Final Guide: Cardiac Arrhythmia, Creatinine, Levator Palpebrae Superioris Muscle
Thyroid and Parathyroid
Learning
objectives
Outline the anatomy of the thyroid gland including blood supply and relation to
the recurrent and external laryngeal nerves
Contrast the embryologic derivations of the superior and inferior parathyroid
glands
Understand the pituitary-thyroid hormonal axis
Contrast the natural history and treatment of follicular with papillary thyroid
carcinoma
Explain the natural history and management of medullary thyroid carcinoma
Recognize anaplastic thyroid carcinoma
Explain the causes, natural history and indications for surgery for multinodular
goitre
Describe the management options for hyperthyroid conditions including Grave’s
disease and a toxic adenoma
Recognize the complications of thyroid surgery
Formulate a differential diagnosis for hypercalcaemia
Discuss the investigation and management of primary hyperparathyroidism
Anatomy Macroscopic
Location - anterior triangle of neck (wrapped around larynx and trachea),
superior border is thyroid and cricoid cartilage
Thyroid - 2 lateral lobes, connecting isthmus, pyramid
4 parathyroid glands (2 per side, each side has superior and inferior) on
posterior thyroid lobes
Microscopic
Follicular cells produce, store and release thyroid hormones (T4
thyroxine + T3 tri-iodothyronine)
C-cells produce calcitonin (Ca lowering hormone)
Blood, nerves
Superior thyroid artery (branch off external carotid artery) -> anterior +
posterior branches -> superior pole of thyroid
Inferior thyroid artery (branch off thyrocervical trunk) -> superior +
inferior branches -> inferior pole of thyroid + all parathyroid glands (risk of hyper-Ca if
dissected)
Superior and middle thyroid veins -> IJV
Inferior thyroid veins -> left and right brachiocephalic veins
SNS supply via superior, middle and inferior cervical ganglion of
sympathetic trunk
PSNS supply via superior laryngeal and recurrent laryngeal nerve (CN X)
Anatomical relationships
Vagus nerve -> superior laryngeal nerve -> internal laryngeal nerve
(sensory to laryngeal mucosa) + external laryngeal nerve (motor to cricothyroid)
oExternal laryngeal descends on the larynx (behind sternothyroid)
to supply cricothyroid
Vagus nerve -> recurrent laryngeal nerve
oLeft RLN loops under aortic arch
oRight RLN loops under right subclavian artery
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Embryology Thyroid
Bipartite midline structure derived from primitive pharynx
Thyroid follicular cells arise from foramen caecum (tongue)
Thyroid gland descends midline from foramen caecum -> level of larynx
where it buds laterally
Neural crest cells (4th branchial cleft + ultimobranchial body) give rise to
parafollicular C cells and a small postero-lateral surface projection (Tubercle of
Zuckerkandl)
Parathyroid
Inferior parathyroid gland arises from 3rd pharyngeal arches (weeks 5-6)
-> thymus pulls parathyroids caudally and medially -> thymus and parathyroids lose
connection -> 40% terminate on lower pole of thyroid & 40% terminate within thymus
Superior parathyroid gland arises from 4th pharyngeal arches (weeks 5-
6) -> parathyroid dissociate from pharynx -> attach to thyroid gland migrating caudally,
but less than thymus/ inferior parathyroids -> 80% terminate on posterolateral aspect of
thyroid
Physiology Pituitary- thyroid hormonal axis
Hypothalamus - release TRH
Anterior pituitary gland - release TSH
Thyroid gland - T3 and T4
oReleased thyroid hormone - 90% T4 (inactive) + 10% T3 (more
biologically active)
oT4 is converted to T3 at tissues (mainly liver)
oMost circulating thyroid hormone is bound to plasma protein (eg
thyroxine binding globulin, albumin)
Negative feedback loop to hypothalamus & anterior pituitary gland
Parathyroids
PTH production -> influences Ca and P metabolism
Increase kidney excretion of P (inhibit tubular resorption) + reduce
kidney excretion of Ca (allow tubular resorption)
Stimulate osteoclastic activity in bone to increase Ca and P release into
blood
Activate 1a-hydroxylase enzymes in kidney to convert calcifediol ->
calcitriol (active vitamin D) for intestinal absorption of Ca
Classification of
disorders
Main groups
Thyroid function - hypothyroidism, hyperthyroidism
Thyroid structure - nodular goitre, thyroid plasms
Specific groups
Embryological defects
Benign thyroid nodules
Multinodular goitre
Thyroid cancer
Thyrotoxicosis
Thyroiditis
Clinical workup of
thyroid nodule
Clinically single thyroid nodules
60-70% are benign nodules (simple thyroid cysts, solitary colloid nodules
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or benign follicular adenomas)
30-40% dominant nodule in multinodular goitre
7% thyroid cancers
<7% area of nodularity within thyroiditis
Clinical presentation
Asymptomatic swelling in neck that moves with swallowing
Benign nodule - local pressure symptoms (dysphagia from oesophageal
pressure, persistent cough or stridor from tracheal pressure, hoarse voice from RLN
pressure, SVC obstruction)
Toxic nodule - thyrotoxicosis sx
Investigations
TFTs (TSH, free T4 and T3, TPO Ab, TG Ab, TSH-R [stim] Ab, TSH-R [block]
Ab)
Normal TSH Conduct thyroid US + FNA
biopsy
High TSH Autoimmune inflammation of
thyroid (Hashimoto)
Conduct another blood test on
serum antibodies
Low TSH Nodule is producing high levels
of TH
Conduct thyroid radioisotope
scan
Imaging
Ultrasound Indication - suspected thyroid nodule, nodular
goitre, nodules incidentally found on other imaging
Determine character - cystic, solid, mixed
Radioisotope
I131 scan
Indication - patient with low TSH (scan after
blood test instead of FNA)
Patient takes small dose of radioactive iodine
pill OR technetium scan injection
Determine if thyroid nodule is hot
(autonomous) or cold (non-functional)
Thyroid nodule absorbs radioiodine -
not cancerous, hot/autonomous/toxic nodule
Thyroid nodule doesn't absorb
radioiodine - 5% risk of cancer, cold nodule
FNA
Description Most accurate predictor of thyroid nodule
malignancy
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Document Summary
Outline the anatomy of the thyroid gland including blood supply and relation to the recurrent and external laryngeal nerves. Contrast the embryologic derivations of the superior and inferior parathyroid glands carcinoma goitre. Contrast the natural history and treatment of follicular with papillary thyroid. Explain the natural history and management of medullary thyroid carcinoma. Explain the causes, natural history and indications for surgery for multinodular. Describe the management options for hyperthyroid conditions including grave"s disease and a toxic adenoma. Discuss the investigation and management of primary hyperparathyroidism. Location - anterior triangle of neck (wrapped around larynx and trachea), superior border is thyroid and cricoid cartilage. Thyroid - 2 lateral lobes, connecting isthmus, pyramid. 4 parathyroid glands (2 per side, each side has superior and inferior) on posterior thyroid lobes. Follicular cells produce, store and release thyroid hormones (t4 thyroxine + t3 tri-iodothyronine) Superior thyroid artery (branch off external carotid artery) -> anterior + posterior branches -> superior pole of thyroid.
