Thyroid Flashcards
What is the role of Thyroid Peroxidase?
Links tyrosine and iodine to form T3 and T4 on thyroglobulin in the thyroid.
-Follicular cells: produce T4 + T3 (more active; most produced in periphery from conversion T4 -> T3)
-Parafollicular C cells: produce calcitonin- lowers calcium
What is thyroglobulin?
Stores T3 and T4 in colloid within the thyroid.
-Level detects recurrence of pap & folic CA after thyroidectomy
What is the function of thyroid binding globulin?
Transports the majority of T4 and T3 in the bloodstream.
Where do T3 and T4 bind?
They bind to thyroid receptors in the nucleus.
What is the T4:T3 serum ratio?
20:1
Which is the more active form of thyroid hormone?
T3 is the more active and potent form.
What is a side effect of thyroxine?
Osteoporosis.
Where do superior parathyroids originate?
From the 4th branchial pouch. Associated with thyroid complex.
-Ectopic most likely to be found in retro or paraesophageal position, 2nd carotid sheath
Where do inferior parathyroids originate?
From the 3rd branchial arch, associated with the thymus.
-Ectopic most likely to be found in thymus, 2nd intrathyroidal
What is the blood supply of the superior thyroid artery?
It is the first branch of the external carotid artery.
What is the blood supply of the inferior thyroid artery?
It branches off the thyrocervical trunk from the subclavian artery. When ligating inferior thyroid artery for thyroidectomy, stay as close to thyroid as possible to avoid injury to parathyroids
Superior laryngeal nerve
Superior laryngeal nerve – motor to cricothyroid (External branch) MC nerve injured in thyroidectomy. Tracks with superior thyroid artery.
- Injury results in loss of projection of voice
- Superior laryngeal nerve (internal branch): sensory to pharynx
Recurrent laryngeal
Recurrent laryngeal – motor to all of larynx except cricothyroid. Tracks with inferior thyroid artery
- Runs in the trachea-esophageal groove
- Left loops around aorta, right loops around innominate
- Unilateral injury can lead to Hoarseness (Vocal cord abducts) or can be asymptomatic (adducts, paramedian position)
- BL injury -> Can either obstruct airway (both cords adducted, in paramedian position) = emergent tracheostomy
- BL injury -> or cause aspiration (both cords abducted)
If recurrent laryngeal nerve injured & not better after 6 weeks -> medialize the vocal cord with silicone wedge injection
-Ligament of Berry- posterior medial suspensory ligament close to RLN
Methamizole & PTU
Methimazole and PTU both inhibit oxidation of iodide to iodine by inhibiting thyroid peroxidase
PTU, propranolol, and steroids inhibits conversion of T4 to T3
-Methimazole: 1st line; inhibits peroxidases (link iodine + tyrosine together) & inhibits iodine-tyrosine coupling; SE= cretinism, aplastic anemia and agranulocytosis
-PTU: inhibits peroxidases & inhibits iodine-tyrosine coupling; OK during pregnancy as it does not cross placenta; SE= aplastic anemia or agranulocytosis
Non-recurrent laryngeal nerve
Right non-recurrent – MC. Arteria lusoria.
- Absent innominate
- R common carotid and subclavian directly off aorta
- R SC artery is retroesophageal and comes off of descending aorta, distal to left subclavian (causes dysphagia lusoria). traverse posterior to esophagus and trachea
Left non-recurrent
- Right sided aortic arch
- L SC directly off aorta
- Ligamentum arteriosum displaced to right
Thyroid nodules
Even if PET scan lights up a thyroid nodule, still follow the guidelines below. Nothing changes.
Best test to assess = US, get this first
Get TSH, T3/T4
If TSH Low: Need to think functional nodule or hyperthyroidism
* Low TSH: ONLY SCENARIO TO GET RADIOACTIVE IODINE UPTAKE SCAN
* If T3/T4 high: hyperthyroidism. Treat. No need for biopsy
* If T3/T/4 normal = subclinical hyperthyroidism: Observe
If TSH normal or high: Need to think cancer or hypothyroidism
* Next, Look at US to see if you need FNA
* Before needle aspiration, must make sure patient is euthyroid
* Perform FNA only if:
1. Nodule ≥ 5 mm and are solid and HYPOECHOIC
2. Nodule > 5 mm AND have any of the following:
- Irregular margins
- Microcalcifications (MOST specific for malignancy),
- Taller than wide shape
- Rim calcifications
- Hypoechoic
FNA indeterminant for thyroid nodule Repeat the FNA
Benign: repeat US in 6-12 months; repeat FNA if it enlarges
Atypia/follicular of Undetermined significant and same on repeat FNA, get molecular testing (lobectomy vs 3 month FNA)
Folicular neoplasm: lobectomy
Thyroid nodule shows colloid on bx = colloid goiter low chance of malignancy. Tx: is thyroxine. lobectomy if continues to enlarge
Thyroid nodule shows normal thyroid tissue and T3/4 elevated likely solitary toxic nodule. If asymptomatic observe. Symptoms methimazole and radioactive iodine
Cystic or spongiform lesions = benign = Do not FNA Cysts!!! Must have solid component
Risk of CA for nodules higher in: Children, <30 years old, history of neck radiation
Thyroid nodules in pediatric have a much higher risk of cancer when compared to adults
PTU: hepatotoxicity
131 – radioactive
123 – thyroid scan
Thyroid storm
-Inc HR, fever, numbness, irritability, v/d, high-output cardiac failure
-MC after surgery in pts w undx Grave’s dz
-Tx= beta blockers, Lugol’s solution (KI), cooling blankets, oxygen, glucose
-Wolff-Chaikoff effect: high dose of iodine -> inhibit TSH action on thyroid; inhibit organic coupling of iodide = less T3 + T4 release
- Lugols solution, given pre-operatively to prevent thyroid storm when operating on Graves
- Aspirin is contraindicated in thyroid storm b/c it decrease t3/t4 protein binding
Goiter
Goiter = thyroid enlargement. MCC is iodine deficiency = replace iodine
Non-toxic multinodular goiter (colloid goiter) - diffuse enlargement but no function abnormality. From low grade TSH stimulation or iodine deficiency
Indications to operate:
- Airway compression (stridor, dyspnea)
- suspicious nodule
- cosmesis
Path shows colloid tissue
Tracheomalacia can occur from compression
Tx: thyroxine
Mediastinal thyroid tissue (substernal goiter) – Mostly from inferior extension of normally placed thyroid gland. (Usually, multinodular goiter).
Blood supply is from cervical, not thoracic
Tx: Surgical resection from cervical incision for ALL, even if asymptomatic - don’t do sternotomy
Pyramidal lobe
Pyramidal lobe: superior extension from thyroid isthmus
-can cause thyroglossal duct cyst= midline cervical mass; moves upward w swallowing; resect bc susceptible to infxn + premalignant
Lingual thyroid
- thyroid tissue in foramen cecum at base of tongue. 2% malignancy. Only thyroid tissue in most.
- These patients are hypothyroid!!
-Sx: dysphagia, dysphonia, dyspnea - Tx: Thyroxine, abolish with radioactive iodine if that fails.
- Resect only if worried about CA.
Toxic multi-nodular goiter
Toxic multi-nodular goiter – will see non-homogenous uptake on thyroid scan – key difference between graves which is homogenous
- Total thyroidectomy 1st line (Only hyperthyroidism to operate first) is BC radioactive iodine is not as effective, has non-hemogenous uptake, but medical treatment should be considered especially in elderly and frail
- Path shows colloid tissue
-Toxic multinodular goiter: F > 50; hyperplasia 2ary to chronic low-grade TSH stimulation; pathology= colloid; can try radioactive iodine but non-homogenous uptake, surgery preferred initial tx
-Single toxic nodule: younger; thioamide + radioactive iodine effective
Solitary Toxic nodule
Usually >3 cm large!!! Young female. methimazole + Radioactive iodine
Graves Disease
Gold standard is radioactive iodine (Contraindicated if exophthalmos, pregnant, breast feeding, thyrotoxicosis)
if doing thyroidectomy. Give methimazole until euthyroid, b blocker, lugols for 14 days prior
Thyroid stimulating immunoglobulin
-Grave’s dz: diffuse uptake of radioactive iodine (RAI), antibodies against TSH receptors
-Exophthalmos, pretibial edema= sx found only in graves
-Sx: a fib, heat intolerance, thirst, inc appetite, weight loss, sweating, palpitations
-Caused by IgG antibodies to TSH receptor, thyroid-stimulating immunoglobulin or thyrotropin receptor
-Dx: low TSH, high T3 + T4; IgG antibodies to TSH receptor, diffuse radioactive iodine uptake
-RAI worsens ophthalmopathy
-Suspicious nodule most common operative reason: preop= methimazole until euthyroid, B blocker, Lugol’s solution for 14 days to decrease friability + vascularity (start only after euthyroid)
Hashimoto’s thyroiditis
Hashimoto’s thyroiditis AKA (chronic thyroiditis) (lymphocytic thyroiditis)
MCC of goiter and hypothyroidism in US
Path shows lymphocytic infiltrate
3x risk of cancer when thyroid nodules are found here
Associated with lymphoma
Antibody: anti-thyroglobulin, anti-microsomal and anti-thyroid peroxidase
-Hashimoto’s: caused by antithyroid antibodies; tx= thyroid replacement
o Acute early stage= thyrotoxicosis
o Humoral & cell-mediated autoimmune disease (microsomal + thyroglobulin antibodies)
o Path= lymphocytic infiltrate
o Goiter= lack of organification of trapped iodine inside gland
