Chapter 22- Thyroid Flashcards
What embryologic structure is the thyroid derived from?
1st and 2nd pharyngeal pouches
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?
Off 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
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 vein
How common are nonrecurrent laryngeal nerves?
2-3%, more common on right
Where does the superior laryngeal nerve run? What does it supply?
Runs lateral 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 does the recurrent laryngeal nerve run? What does it supply?
Runs posterior to thyroid lobes in the tracheoesophageal groove, can track with inferior thyroid a., L. loops around aorta, R. loops around right sublclavian; provides motor to all of the larynx except cricothyroid
What does injury to the recurrent laryngeal nerve cause?
Hoarseness; bilateral injury can obstruct airway needing emergent trach
Where is the ligament of Berry?
Posterior medial suspensory ligament close to RLNs; careful dissection
That is thyroglobulin?
Stores 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
What is the most sensitive lab indicator of gland function?
TSH
What does thyroid-binding globulin do?
Thyroid hormone transport; T3/T4 also binds albumin
Where are the Tubercles of Zuckerkandl?
Most lateral, posterior extension of thyroid tissue; rotate medially to find RLNs; left behind in subtotal thyroidectomies
What do parafollicular C cells produce?
Calcitonin
What is the resin T3 uptake measure?
Mesures 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 postthyroidectomy stridor?
Open neck and remove hematoma; can result in airway compromise
Symptoms of thyroid storm?
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
Treatment for thyroid storm?
Beta-blockers, PTU, Lugol’s solution (KI), 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?
Thyroid function tests: if elevated, give thyroxine (nodule should regress within 6mo); if not elevated, proceed to FNA
2nd step in workup of asymptomatic thyroid nodule when TFTs are normal?
FNA (determinant in 75-90%)
Treatment when FNA shows follicular cells?
Thyroidectomy or lobectomy (5-10% malignancy risk)
Treatment when FNA shows thyroid CA?
Thyroidectomy or lobectomy
Treatment when FNA shows cyst fluid?
Drain fluid; if it recurs, thyroidectomy or lobectomy
Treatment when FNA shows colloid tissue
Most likely colloid goiter; low chance of malignancy (<1%); treatment: thyroxine, thyroidectomy or lobectomy if it enlarges
Next step in workup of asymptomatic thyroid nodule if FNA is indeterminant (10-25%)?
Radionuclide study
Treatment for hot nodule on radionuclide study?
Thyroxine for 6mo; if size does not go down, lobectomy
Treatment for cold nodule on radionuclide study?
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
What is a primary vs. secondary goiter?
Primary (rare): vessels originate from innominate artery; secondary: vessels originate from superior and inferior thyroid arteries
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
Lungual 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
Mechanism of action of propylthiouracil?
Inhibits peroxidases and prevents DIT and MIT coupling
Side effects of PTU?
Aplastic anemia, agranulocytosis
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
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, atrial fibrilation, heart dysfunction, heat intolerance, thirst, increased appetite, weight loss, sweating, palpitations
Cause of Graves’ disease?
IgG antibodies to TSH receptor (long-activng thyroid stimulatory, thyroid-stimulating immunoglobulin)
Diagnosis of graves’ disease?
Increased 123I uptake diffusely in thyrotoxic patient with goiter; LATS level, decreased TSH, increased T3/T4
Treatment of Graves’ disease?
Thioamides (70% recurrenc), 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?
Normal
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 scan
% 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; partial thyroidectomy if continues to grow, if nodules appear, or compression symptoms occur
What is the most common cause 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?
Woody, fibrous component that can involve adjacent strap muscles and carotid sheath; can resemble thyroid CA or lymphoma (need biospy)
Complications of Riedel’s fibrous struma?
Hypothyroidism and compression symptoms
Conditions associated with Riedel’s fibrous struma?
Sclerosing cholangitis, fibrotic diseases, methysergide treatment, retroperitoneal fibrosis
Treatment for Reidel’s fibrous struma?
Steroids and thyroxine; may need isthmectomy or tracheostomy
What is the most common endocrine malignancy in the US?
Thyroid cancer
Characteristics of 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 malignany
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 factor predicts a worse prognosis for papillary thyroid carcinoma?
Older age (>40-50y)
Prognosis of papillary thyroid carcinoma is based on what?
Local invasion
Papillary carcinoma mets most commonly go where?
Lung
What does pathology of papillary carcinoma show?
Psammoma bodies (calcium) and Orphan Annie nuclei
Treatment for <1cm papillary carcinoma?
Lobectomy
What are the indications for total thyroidectomy with papillary carcinoma?
Bilateral, multicentricity, history of XRT, positive margins, tumors >1cm
Treatment for clinically positive cervical nodes or extrathyroidal tissue involvement with papillary/follicular carcinoma?
Ipsilateral MRND
Treatment for metastatic disease, residual local disease, positive lymph nodes or capsular invasion with papillary carcinoma?
131I 6 wks after surgery
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%
WWhat does FNA show with follicular carcinoma?
Follicular cells; 10% chance of malignancy, need thyroidectomy
Treatment for adenoma or follicular cell hyperplasia?
Lobectomy
Treatment for follicular carcinoma >1cm or extrathyroidal?
Total thyroidectomy
Treatment for follicular carcinoma >1cm or extrathyroidal disease?
131I 6 wks after surgery
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; C-cell hyperplasia considered premalignant
Pathology of medullary carcinoma shows what?
Amyloid deposition
What test can be used to look for medullary thyroid carcinoma?
Gastrin; caused an increase in calcitonin
What do you need to screen for when a patient has been diagnosed with medullary carcinoma?
Hyperparathyroidism and pheochromocytoma
Where does follicular carcinoma mets go?
Lung, liver, bone
Treatment for medullary carcinoma?
Total thyroidectomy with central neck node dissection
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?
Prophylactic thyroidectomy and central node dissection at age 2
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
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
