Chapter 22- Thyroid+ Flashcards
What embryologic structures are the thyroid derived from?
- 1st and 2nd pharyngeal pouches
- Tissue from foramen cecum at base of tongue
- Migrates inferior through thyroglossal duct
- 4th pouch contributes c-cells
Where is thyrotropin-releasing factor released from? What does it act on?
Hypothalamus; acts on anterior pituitary gland and causes release of TSH.
Where is TSH released from? What are its effects?
Anterior pituitary gland; acts on thyroid to release T3 and T4
How are TRH and TSH release regulated?
By T3 and T4 via negative feedback loop
Where does the superior thyroid artery originate?
1st branch of external carotid
What is the origin of the inferior thyroid artery?
Thyrocervical trunk; supplies inferior AND superior parathyroids
Where should the inferior thyroid artery be ligated during thyroidectomy?
Close to thyroid to avoid injury to parathyroid glands and nerves
What is the Ima artery?
Occurs in 1%, arises from innominate or aorta and goes to the isthmus
Where do the superior and middle thyroid veins drain?
Internal jugular
Where does the inferior thyroid vein drain?
Innominate (brachiocephalic) vein
How common are nonrecurrent laryngeal nerves?
2-3%, more common on right. Comes right off vagus.
Where does the superior laryngeal nerve run? What does it supply?
Runs laterally to thyroid lobes, close to superior thyroid artery; motor to cricothyroid.
What does loss of superior laryngeal nerve cause?
Loss of projection and easy voice fatigability (opera singers).
Where do the recurrent laryngeal nerves run? What do they innervate?
- Runs posterior to thyroid lobes in the tracheoesophageal groove
- Can track with inferior thyroid artery
- L. loops around aorta.
- R. loops around right sublclavian.
- Provides motor to all of the larynx except cricothyroid (ext br of superior laryngeal n).
What does injury to the recurrent laryngeal nerve cause?
Hoarseness; bilateral injury can obstruct airway needing airway control, laryngoscopy, possibly emergent trach.
Scenario will be a purposefully sacrificed nerve 2/2 invasion, and a nonvisualized contralateral nerve.
What is and where is the ligament of Berry?
Posterior medial thyroid suspensory ligament close to RLNs; use careful dissection around this area.
There are often small branches from the inferior thyroid, so if bleeding occurs, hold pressure and identify the nerve before ligating/cauterizing.
What is the function of thyroglobulin?
Precursor to production of and storage of T3/T4 in colloid.
What is the plasma T4:T3 ratio?
15:1
Is T3 or T4 more biologically active?
T3; most produced in periphery by T4 to T3 conversion by peroxidases
What enzyme links/separates tyrosine and iodine?
Peroxidase (drug target)
What is the most sensitive lab indicator of gland function?
TSH. This is the first lab test for thyroid nodule workup. US and FNA are the other two required tests.
What does thyroid-binding globulin do?
Thyroid hormone transport; T3/T4 also binds albumin
Can be followed postop thyroidectomy after PTC.
Where are the Tubercles of Zuckerkandl?
Most lateral, posterior extension of thyroid tissue; rotate medially to find RLNs; left behind in subtotal thyroidectomies (not done often, only for benign dz)
What do parafollicular C cells produce?
- Calcitonin
- counteracts PTH
- lowers Ca by inhibiting osteoclasts
- increased in MTC
What is the resin T3 uptake measure?
- Measures free T3 by having it bind resin
- Increased uptake = hyperthyroidism or low TBG
- Decreased uptake = hypothyroidism or high TBG
What should TSH levels do with thyroxine treatment?
Fall to 50%
What is a long-term side effect of thyroxine?
Osteoporosis
What is the treatment for post-thyroidectomy stridor and neck swelling?
- Impending airway compromise
- Suspect hematoma
- Emergent bedside decompression
- Re-open neck down past strap muscles
- Secure airway w/ ETT
- OR for wound exploration
- Hx: M w/ Grave’s and previous neck surgery
Symptoms of thyroid storm?
- Ramped up metabolism: Tachycardia, fever
- Numbness, irritability
- Vomiting, diarrhea
- High output cardiac failure
Thyroid storm can be precipitated by what?
Post-op in undiagnosed Grave’s disease, anxiety, excessive palpation of the gland, adrenergic stimulants.
Make sure a Grave’s thyroidectomy is euthyroid pre-op.
Treatment for thyroid storm?
- Beta-blockers
- PTU (propylthiouracil) - blocks T4-to-T3 conversion
- (Methimazole is less hepatotoxic and preferred in non-life-threatening situations, but cannot be administered as regularly; PTU also better in pregnancy)
- Lugol’s solution (KI) - Wolff-Chaikoff effect dec synthesis
- cooling blankets, oxygen, glucose, fluid
What is the Wolff-Chaikoff effect?
High doses of iodine (Lugol’s solution), which inhibits TSH action on thyroid and inhibits organic coupling of iodide, resulting in less T3/T4
What is the 1st step in workup of asymptomatic thyroid nodule?
TSH. Ultrasound can also be done in conjunction. FNA if concern.
Treatment when FNA shows follicular cells?
Thyroidectomy or lobectomy (5-10% malignancy risk)
Treatment when FNA shows thyroid CA?
Thyroidectomy or lobectomy
- lobectomy if <4cm, no extrathyroid extension, no LN mets
- thyroidectomy if >4cm, extrathyroid extension, lymph node mets, >45yr old, hx of radx to head/neck, fam hx of thyroid cancer
Treatment when FNA shows cyst fluid?
Drain fluid; if it recurs, thyroidectomy or lobectomy
Treatment when FNA shows colloid tissue
- Likely colloid goiter; low chance of malignancy (<1%)
- Mgmt: thyroxine, thyroidectomy or lobectomy if it enlarges
Next step in workup of asymptomatic thyroid nodule if FNA is indeterminant (10-25%)?
Redo FNA. Consider thyroidectomy if imaging is concerning.
Treatment for hot nodule on radionuclide study?
- Solitary toxic nodule
- Can attempt Thyroxine for 6mo
- If size does not go down, do lobectomy
Treatment for cold nodule on radionuclide study?
Biopsy and likely thyroidectomy or lobectomy (more likely malignant than hot nodule)
% of thyroid nodules that are benign?
85%
1 cause of goiter?
Iodine deficiency
Treatment for goiter?
Iodine replacement
Definition of nontoxic goiter?
Diffuse enlargement without evidence of functional abnormality
Treatment of nontoxic goiter?
Suppress with thyroxine; 131I, thioamides, subtotal thyroidectomy or lobectomy on side of goiter if medical treatment ineffective
Where does mediastinal thyroid tissue come from?
Most likely from acquired disease with inferior extensions of a normally placed gland
% with pyramidal lobe?
10%; extends from isthmus toward the thymus
Where is a lingual thyroid found?
Thyroid tissue that persists in the are of the foramen cecum at the base of the tongue
Symptoms of lingual thyroid?
Dysphagia, dyspnea, dysphonia
% malignancy risk with lingual thyroid?
2%
Treatment of lingual thyroid?
Thyroxine suppression; abolish with 131I or resection if enlarged
Lingual thyroid is the only thyroid tissue in what % of patients that have it?
70%
Classic sign of thyroglossal duct cyst?
Moves upward with swallowing
Complications of thyroglossal duct cyst?
Can be premalignant, susceptible to infection
Treatment for thyroglossal duct cyst?
Resection; need to take midportion or all of hyoid bone along with the thyroglossal duct cyst
Use of propylthiouracil and methimazole?
Good for young patients, small goiters, mild T3/T4 elevation.
Can be frustrating to get good levels, so patients often end up with surgery or ablation. This treatment is often not definitive.
Mechanism of action of propylthiouracil?
Inhibits peroxidases and prevents DIT and MIT coupling
Side effects of PTU?
- Aplastic anemia, agranulocytosis
- Inc hepatotoxicity compared to methimazole
- Also is not as rapid and does not last as long - requires strict and frequent dosing
MOA of methimazole?
Inhibits peroxidases and prevents DIT and MIT coupling
Side effects of methimazole?
Cretinism in newborns (crosses the placenta), aplastic anemia or agranulocytosis
When is radioactive iodine used?
In patients who are poor surgical risks or unresponsive to PTU.
Can exacerbate Grave’s, and the post-procedural care is a hassle, so many patients opt for surgery if they are candidates.
When is the best time to perform thyroidectomy in pregnant patients?
2nd trimester; decreased risk of teratogenic events and premature labor
Most common cause of hyperthyroidism?
Graves’ disease (80%)
Signs of Graves’ disease?
More common in women; exophthalmos, pretibial edema, a-fib, heart dysfunction, heat intolerance, thirst, increased appetite, weight loss, sweating, palpitations
Cause of Graves’ disease?
IgG antibodies to TSH receptor (long-acting thyroid stimulatory, thyroid-stimulating immunoglobulin)
Diagnosis of graves’ disease?
Scintigraphy shows increased 123I uptake diffusely in thyrotoxic patient with goiter; LATS level, decreased TSH, increased T3/T4
Treatment of Graves’ disease?
Thioamides (70% recurrence), 131I (10% recurrence), subtotal thyroidectomy or total thyroidectomy with thyroxine replacement if medical therapy fails
Preop preparation prior to thyroidectomy for Graves’ disease?
PTU or methimazole until euthyroid, beta-blocker 1 week before surgery, Lugol’s solution 10-15d to decrease friability and vascularity
Indications for surgery for Graves’ disease?
Noncompliant patient, recurrence after medical therapy, children, pregnant women not controlled with medical therapy, or concomitant suspicious thyroid nodule
What is the most common cause of thyroid enlargement?
Toxic multinodular goiter
TFTs seen in toxic multinodular goiter?
Often normal, but can show hyperthyroid labs
Symptoms of toxic multinodular goiter?
Cardiac symptoms, weight loss, insomnia, airway compromise; symptoms can be precipitated by contrast dyes
What is toxic mutinodular goiter caused by?
Hyperplasia secondary to chronic low-grade TSH stimulation
Treatment of toxic multinodular goiter?
131I and thioamides; subtotal thyroidectomy if medical treatment ineffective
Presentation of single toxic nodule?
Women; younger; can cause cervical compression
Diagnosis of single toxic nodule?
Thyroid scintigraphy shows single hot nodule
% of hot nodules that will cause symptoms?
20%
Treatment of single toxic nodule?
131I and thioamides; lobectomy if medical treatment ineffective
Most common cause of hypothyroidism in adults?
Hashimoto’s disease
Cause of Hashimoto’s disease?
Humeral and cell-mediated autoimmune disease (microsomal and thyroglobulin antibodies)
What is the goiter of Hashimoto’s disease caused by?
Secondary to lack of organification of trapped iodide inside gland
Pathology of Hashimoto’s disease?
Lymphocytic infiltrate
Treatment for Hashimoto’s disease?
1st line: thyroxine for hypothyroidism
Partial thyroidectomy if continues to grow, if nodules appear, or compression symptoms occur
What is the most common mechanism of bacterial thyroiditis?
Contiguous spread
Signs/symptoms of bacterial thyroiditis?
Normal TFTs, fever, dysphagia, tenderness
Treatment for bacterial thyroiditis?
Antibiotics; may need lobectomy to r/o cancer in pt with unilateral swelling and tenderness
Signs/symptoms of DeQuervain’s thyroiditis?
Viral URI, tender thyroid, sore throat, mass, weakness, fatigue, elevated ESR
DeQuervain’s thyroiditis is associated with hypo-, hyper-, or euthyroidism?
Hyperthyroidism
Treatment for DeQuervain’s thyroiditis?
- Steroids and ASA
- May need lobectomy to r/o cancer in pts with unilateral swelling and tenderness
What is Riedel’s fibrous struma?
- Infiltrative disease.
- Woody, fibrous component
- Can involve adjacent strap muscles and carotid sheath (most other infiltrative types of thyroiditis are limited to the thyroid)
- Can resemble thyroid CA or lymphoma - need biospy
- Very rare
Complications of Riedel’s fibrous struma?
Hypothyroidism and compression symptoms (only infiltrative type that can locally spread)
Conditions associated with Riedel’s fibrous struma?
Sclerosing cholangitis, fibrotic diseases, methysergide treatment, retroperitoneal fibrosis
Treatment for Reidel’s fibrous struma?
- Treat the infiltration - steroids
- Treat the hypothyroidism, if present - thyroxine
- Treat the compression, if present - isthmectomy or tracheostomy
What is the most common endocrine malignancy in the US?
Thyroid cancer
Characteristics of thyroid tumor worrisome for malignancy?
Solid, solitary, cold, slow growing, hard; male, age >50, previous neck XRT, MEN IIa or IIb
What does sudden growth of thyroid tumor imply?
Hemorrhage into previously undetected nodule or malignancy
How are thyroid adenomas differentiated from carcinomas?
Require lobectomy
What is the cancer risk of follicular adenomas?
No increase in cancer risk; still need lobectomy to prove it is adenoma
What is the most common thyroid carcinoma?
Papillary thyroid carcinoma (80-90%)
Which thyroid cancer is the slowest growing, least aggressive, with the best prognosis?
Papillary thyroid carcinoma
What is the most common tumor following neck XRT?
Papillary thyroid carcinoma
What patient factor predicts a worse prognosis for papillary thyroid carcinoma?
Older age (>40-50y)
Prognosis of papillary thyroid carcinoma is based on what?
- Local invasion
- Spreads to lymph nodes (doesn’t affect prognosis)
- Most common, assd w/ radiation to neck
Papillary carcinoma mets most commonly go where?
Lung
What does pathology of papillary carcinoma show?
- Psammoma bodies (calcium)
- Orphan Annie nuclei (washed out/clear nuclei)
Treatment for <1cm papillary carcinoma (young and with negative nodes)?
Lobectomy. Usually you will do total thyroidectomy.
What are the indications for total thyroidectomy with papillary carcinoma?
Bilateral, multicentricity, history of XRT, positive margins, tumors >1cm
Multifocal disease is common, need to remove it all b/c local invasion is prognostic. Remember that thyroglobulin is used to detect recurrence, and lobectomy prevents this.
Treatment for clinically positive cervical nodes or extrathyroidal tissue involvement with papillary/follicular carcinoma?
- ipsilateral modified radical neck dissection - lvl 2-5 nodes
- central neck dissection - lvl 6 nodes
- path may say aberrant thyroid tissue - this is cancer
Treatment for metastatic disease, residual local disease, positive lymph nodes or capsular invasion with papillary carcinoma?
131I 6 wks after surgery
Ideally want TSH elevated, so hold replacement hormone or give rTSH.
5 year survival with papillary carcinoma?
95%; death secondary to local disease
How does follicular thyroid carcinoma spread?
Hematogenous spread (to bone most common)
What % of follicular carcinoma is metastatic at time of presentation?
50%, just like MTC
What does FNA show with follicular carcinoma?
Often just Follicular cells - 10% chance of malignancy, need lobectomy if this is shown on FNA.
If cancer is shown on the pathology, then consider completion total thyroidectomy unless low risk.
Treatment for adenoma or follicular cell hyperplasia?
Lobectomy
Treatment for follicular carcinoma >1cm or extrathyroidal?
Total thyroidectomy
Also for angioinvasion or distant metastasis
Treatment for follicular carcinoma >1cm or extrathyroidal disease?
Same management as papillary: based on size, extension, nodal involvement
- total thyroidectomy for 4 cm in diameter or greater, there is extrathyroidal extension of tumor, or there are metastases to lymph nodes or distant sites
- 131I 6 wks after surgery for distant metastases, macroscopic tumor invasion, and/or incomplete tumor resection
- levothyroxine for hypothyroidism and suppression of TSH (prevent growth)
5 year survival for follicular carcinoma?
70%; prognosis based on stage
Syndrome associated with medullary thyroid carcinoma?
MEN IIa and IIb
What cells do medullary thyroid carcinoma arise from?
Parafollicular C cells (neural crest); C-cell hyperplasia considered premalignant. This is why calcitonin can be increased in MTC.
Pathology of medullary carcinoma shows what?
Amyloid deposition
What test can be used to look for medullary thyroid carcinoma?
Pentagastrin stim to confirm high calcitonin. This is done in Europe. US sticks to FNA w/ immunohistochemical staining for calcitonin.
50% secrete CEA.
What do you need to screen for when a patient has been diagnosed with medullary carcinoma?
Hyperparathyroidism and pheochromocytoma (MEN II)
Where do follicular carcinoma mets go?
Lung, liver, bone
Treatment for medullary carcinoma?
- Total thyroidectomy w/ central neck node dissection (level 6).
- Positive lateral nodes: add lateral neck dissection (levels 2-6).
- Postop surveillance: calcitonin and CEA q6m x2, then yearly.
When is MRND indicated with medullary carcinoma?
Clinically positive nodes (bilateral MRND if tumor on both sides of thyroid), or with extrathyroidal disease
Treatment for MEN IIa or IIb?
- Ppx thyroidectomy and CND before 2yrs in IIb, or 6yrs in IIa
- Eval for pheo before thyroidectomy
- Adrenalectomy before thyroidectomy
- Hyperparathyroidism should get surgery if symptomatic or marked hyperCa, kidney stones, marked hyperCaUr, bone loss
5 year survival with medullary carcinoma?
50%; prognosis based on presence of regional and distant mets
Hurthle cell mets go where?
Early nodal spread if malignant, bone and lung
Treatment for Hurthle cell carcinoma?
Total thyroidectomy; MRND for clinically positive nodes
Characteristics of patients with anaplastic thyroid cancer?
Elderly patients with long-standing goiter
5 year survival for anaplastic thyroid cancer?
0%; usually beyond surgical management by diagnosis
Treatment for anaplastic thyroid cancer?
Total thyroidectomy for rare resectable lesion; palliative thyroidectomy for compressive symptoms, palliative chemo/XRT
What carcinomas is XRT effective for?
Papillary, follicular, medullary, Hurthle cell
Not anaplastic
What carcinomas is 131I effective for?
Papillary and follicular thyroid cancer only
Side effects of 131I?
Sialoadenitis, GI symptoms, infertility, bone marrow suppression, parathyroid dysfunction, leukemia
When is the best time to 131I scan for mets?
4-6 weeks after thyroidectomy when TSH levels are highest
In your dissection of the thyroid, when should you expect to see the superior parathyroid?
When you are dissecting the lobe free, lateral to medial, lifting the thyroid away, and ligating the superior pole branches. It will be just posterior to the insertion of the RLN. Gently free it from this tissue to preserve it.
In dissecting a thyroid lobe, how can you find the insertion of the RLN?
Find the inferior cornu of the hyoid bone. The RLN enters the cricopharyngeus in close proximity to the cornu. It moves through Berry’s ligament. Once the inferior thyroid artery is identified, look for the RLN, and do not use electrocautery.
During thyroidectomy, how can the inferior parathyroid be identified?
Once the RLN has been identified, the inferior parathyroid can be found on the inferior posterior surface of the thyroid, anterior to the nerve. It’s often attached to the capsule.
What is the treatment for post-thyroidectomy stridor without neck swelling?
- Be sure there is no hematoma
- Secure airway
- Suspect bilateral RLN
- Flexible fiberoptic laryngoscopy
- can see edema, spasm as well
- If extubating, do immediate flex laryngoscopy to document vocal cord fct
- If failed extubation, can retry, but consider trach
What do you do for a post-op thyroidectomy patient with hoarseness?
- if early and w/o compromise, can assume ETT
- if lasts 3 months, do dx laryngoscopy
- lasting 1 year is likely permanent
- paresis should occur at <5% rate
- paralysis should occur at <2% rate
What is the most common side effect of thyroidectomy?
- hypocalcemia
- perioral tingling or numbness, muscle spasm
- can be transient 2/2 manipulation
- fct returns in 6 wks
- auto-transplant fct returns in 12 wks
- supplement patients with calcium and vit D
- neuromuscular findings require IV replacement
Is routine calcium and vit D supplementation required after thyroid lobectomy?
No. Only for total thyroidectomy.
In summary, what are the locations of the important nerves in a thyroidectomy?
- The recurrent nerve is in the paratracheal space behind the thyroid, runs in the tracheoesophageal groove, inserts under the cricopharyngeus muscle at level of cricoid cartilage.
- A nonrecurrent nerve will branch directly off the vagus, but this is rare and generally only occurs on the right side.
- The superior laryngeal nerve can be seen on the larynx near the superior pole of the thyroid.
What are some important questions to ask in patients with thyroid nodule?
- fam hx of endocrine problems
- exposure to radiation
- activity - palpitations, bilateral fine tremor
- compression
Other than US and FNA, what is a necessary test in a patient who presents with a thyroid nodule and decreased TSH?
- get a scintigraphy - distinguish between Grave’s, solitary nodule, multinodular goiter
What are concerning characteristics on thyroid ultrasound in a patient that presents with a nodule?
- microcalcifications
- hypoechogenicity
- taller than wide
- irregular margins
On thyroid US for a nodule, what is the size cutoff for FNA?
1 cm if concerning findings. Absolute cutoff is 1.5 cm.
This is an office procedure.
Bethesda characteristics and follow up for thyroid FNA
- discordant with imaging - repeat FNA now
- benign - repeat US and FNA in 6 months
- nondiagnostic - repeat FNA now, or do genetic tests
- if 2nd indeterminate, can do lobectomy for dx
- follicular cells of undetx sig - repeat FNA now
- follicular neoplasm - lobectomy (can’t r/o ca w/ FNA)
- suspicious - lobectomy w/ possible completion pending path
- malignant - lobectomy or total thyroidectomy
When is RAI administered postoperatively for thyroid cancer?
- extrathyroidal extension
- distant mets
- consider if positive nodes and tumors >4cm
When is central neck dissection recommended for thyroid cancer?
- these are level VI nodes
- clinically positive central nodes
- clinically positive lateral neck nodes
- large tumors >4 cm
- MTC
When is lateral neck dissection warranted for thyroid cancer?
- these are level II-V nodes
- clinically positive lateral neck nodes
How can levothyroxine help prevent thyroid cancer recurrence?
Suppressing TSH can prevent tumor recurrence
In hyperthyroidism, when is PTU indicated?
- currently pregnant women
- thyroid storm
Positive prognostic mnemonic
- Age - younger is better
- Metastasis - none
- Extent - non-invasive
- Sex/Size - female, <4cm; better if <1cm
Treatment for 4cm thyroid differentiated cancer?
- total thyroidectomy
- consider ppx central node dissection (lvl VI) if higher risk
- consider postop RAI if higher risk
- postop thyroid hormone for TSH suppression
- postop thyroglobulin surveillance
What is the role for chemotherapy in thyroid cancer?
- PTL/ thyroid lymphoma
- metastatic/stage IV disease
Can molecular marker testing be used for exclusion of cancer?
No. It is a highly specific test, but not sensitive enough to rule out disease. It is, therefore, a “rule in” test.
What do you do if your thyroid FNA shows up as MTC?
- path shows chromogranin, CEA, no Tg
- gene testing to check for RET
- rule out pheo - resect first if found
- rule out hyperparathyroidism - calcium and PTH
- preop calcitonin and CEA
- preop CT or MRI for distant mets (no PET): chest is common
- central neck dissection along with thyroidectomy
- if abnormal lateral nodes, do lateral dissection (II-VI)
- if elevated calcitonin >200, do bilateral lateral neck dissection
- surveillance w/ CEA and calcitonin
