Thryoid Flashcards
During embryology, when does the thyroid develop?
- During the third week of gestation the thyroid forms at the base of the tongue between the first pair of pharyngeal pouches, in an area called the foramen cecum
- Then descends to its usual location and develops into the bilobed organ with an isthmus. The thryoglossal duct obliterates during the second month of gestation.
- Parafollicular cells from the ultimobrachial bodies enter the thyroid during its descent.
- Iodine trapping and T4 synthesis begins during the third and fourth months of gestation
In what percent of the population is a pyramidal lobe of the thyroid present?
80%
What is a pyramidal lobe of the thyroid?
An extra lobe that arises most commonly from the isthmus, although can arise from either lateral lobe (left more common), and ascends as far as the hyiod bone.
How much does a normal thyroid gland weigh?
20-25 grams
What muscles overlie the thyroid gland?
Sternohyoid, sternothyroid, thyrohyoid, omohyoid
What structure lies behind the thyroid gland?
Trachea
What structures lie posterolateral to the thyroid gland?
Common carotid arteries, internal jugular veins, vagus nerves
Where are C-cells located?
Within the fobrovascular stroma of the thyroid follicles
What is the origin of the superior thyroid arteries?
The first branch of the external carotid at the level of the carotid bifurcation
What is the origin of the inferior thyroid arteries?
The thyrocervical trunk of the subclavian artery
What is the thyroidea ima artery?
An accessory artery arising from the brachiocephalic trunk (innominate artery) or aortic arch, which ascends anterior to the trachea to the inferior thyroid. It is present in 3-10% of the population.
What is one anatomic explanation for the relatively high frequency of multifocal tumors of the thyroid?
Intraglandular lymphatics
Describe the venous drainage of the thyroid?
The superior thyroid veins drain to the internal jugular, the middle thyroid veins drain to the internal jugular, the inferior thyroid veins drain to the brachiocephalic veins.
Describe the path of the right recurrent laryngeal nerve.
Branches from the vagus nerve and loops under the right subclavian artery. Then ascends to the larynx posterior to the thyroid gland between the trachea and esophagus. It may be either 1 cm anterior or posterior to the inferior thyroid artery.
Describe the path of the left recurrent laryngeal nerve.
Branches from the vagus lateral to the ligamentum arteriosum, runs inder the aortic arch and then ascends along the tracheoesophageal groove to the larynx.
What is the origin of the sympathetic innervation to the thyroid gland?
Vasomotor innervation from the superior and middle cervical sympathetic ganglia
What is the origin of the parasympathetic innervation of the thyroid gland?
Branches of the vagus via the laryngeal nerves.
What is the function of the recurrent laryngeal nerves?
Innervation of all the intrisic muscles of the larynx except the cricothyroid, and sensory innervation to the mucous membranes below the vocal cords
What are the consequences of damage to the recurrent laryngeal nerve?
Ipsilateral vocal cord paralysis resulting in hoarseness or sometimes SOB due to narrowing of the airway
Describe the formation of thyroid hormone.
Iodide is actively transported into the epithelial cells of thyroid follicles, where it is concentrated to 30x its serum concentration. Iodide is oxidized to iodine and combined with tyrosine within the thyroglobulin molecule, resulting in mono- and di-iodinated tyrosines. Mono- and di- iodotyrosine are then coupled to make T3 or T4 depending on the starting constituents.
What cells synthesize thyroglobulin?
Synthesized and secreted from the endoplasmitc reticulum and Golgi apparatus of the thyroid follicular cells.
What are the effects of TSH within the thyroid gland?
- Thyroglobulin proteolysis, causing the release of bound T3/T4 into circulation (onset within 30 min)
- Iodide trapping
- Increased iodination and coupling forming more thyroid hormones
- Increase size and secretions of thyroid cells
- Changes epithelium from cuboidal to columnar, with increased number of cells along the basement membrane.
What effects does thyroid hormone have on the cardiovascular system?
Increased HR, increased CO, increased blood flow, Increased blood volume, increased pulse pressure without change in the MAP
What are the effects of thyroid hormone on the respiratory system?
Increased respiratory rate, increased depth of respiration.
What are the effects of thyroid hormone on the GI tract?
Increased motility
What are the effects of thyroid hormone on the CNS?
Nervousness and anxiety
What are the effects of thyroid hormone on the musculoskeletal system?
Increased reactivity up to a point, then response is weakened and ultimately results in a fine motor tremor.
What are the effects of thyroid hormone on sleep?
Causes constant fatigue with decreased ability to actually sleep.
What effects does thyroid hormone have on nutrition?
Increases basal metabolic rate, increases the need for vitamins, increases metabolism of carbohydrates, lipids, and proteins, decreases weight.
How long does the stored thryoig hormone in follicles last without any increased thyroid hormone production?
2-3 months.
What is the effect of increased TBG on total and free T4?
Total T4 changes, but free T4 remains the same.
What percentage of patients with a lingual thyroid have other functioning thyroid tissue?
30%
What are the congenital anomalies that affect the thyroid?
Complete failure to develop, incomplete descent (lingual or subhyoid position), excessive descent (substernal thyroid), malformation of branchial pouch, persistent sunys tract remnant of developing gland (can lead to thyroglossal duct cyst), lateral aberrant thyroid
What is a thyroglossal duct cyst, and what is the surgical management?
The most common congenital anomaly of the thyroid gland with generally few symptoms, but may become infected. It is easier to see with the tongue sticking out. Surgical excision involves removing the duct remnant and the central portion of the hyoid bone.
What percent of patients with hyperthyroidism have atrial fibrillation that is refractory to medical management?
10%
What are the six major causes of hyperthyroidism?
- Graves’ Disease
- Toxic nodular goiter
- Toxic thyroid adenoma
- Subacute thyroiditis
- Functional metastatic thyroid cancer
- Struma ovarii
What percent of the population is affected by Graves’ disease?
2% of American women
What is the male to female ratio of Graves’ disease?
1:6
What is the average age of onset of Graves’ Disease?
20-40
What are the most common presenting symptoms of Graves disease?
Present in >90%: Nervousness, increased sweating, tachycardia, goiter, pretibial myxedema, tremor.
Present in 50-90%: Heat intolerance, palpitations, fatigue, weight loss, dyspnea, weakness, increased appetite, eye complaints, thyroid bruit
Other: Amenorrhea, decreased libido and fertility
What are typical labs of hyperthyroidism?
Decreased TSH, increased T3 and/or T4, increased thyroid receptor antibodies (TrAb)
What are the three modalities of treatment for hyperthyroidism?
- Antithyroid drugs
- Ablation with I-131
- Subtotal or total thyroidectomy
What is the most common outcome of radioablation iodine therapy?
Euthyroid within 2 months. Eventually with require thyroid homorne replacement.
What population is Iodine radioablation therapy contraindicated in?
Pregnant women and young children.
What are the medical therapies for hyperthyroidism?
- Beta-blockers for symptomatic relief
- Propylthiouracil
- Methimazole
What are the side effects of antithyroid medications?
Rash, fever, peripheral neurotis
What is Plummer’s Disease?
An eponym for toxic nodular goiter.
What is the treatment of choice for toxic nodular goiter?
Surgery. Medical therapy may alleviate symptoms but is less effective than in Graves’ disease, and ablation has a high failure rate.
What are the three major risks following thyroid surgery?
- Injury to the recurrent laryngeal nerve
- Hypoparathyroidism
- Persistent hyperthyroidism when subtotal thyroidectomy is performed
What are the major precipitators of thyroid storm?
Infection, labor, surgery, iodide administration, or recent radioablation
How does thyroid storm present?
Disoriented, febrile, tachycardic, and often are vomiting and have diarrhea
What is the treatment for thyroid storm?
Fluids, antithyroid medications, beta-blockers, sodium-iodine, Lugol’s solution, hydrocortisone, and cooling blankets.
What is Lugol’s solution?
A source of elemental iodine and potassium iodide.
What are the major causes of hypothyroidism?
Autoimmune thyroiditis, iatrogenic, iodine deficiency, dyshormonogenesis.
When should thyroid hormone replacement be started in a hypothyroid infant?
Immediately. Will decrease the neurologic and intellectual deficits.
What are the signs/symptoms of hypothyroidism in infants/children?
Down’s-like facies, FTT, and mental retardation
What are the characteristic signs/symptoms of hypothyroidism in adults?
80% female, fatigue, weight gain, cold intolerance, constipation, menorrhagia, decreased libido and fertility.
Less common complaints include yellow-tinged skin, hair loss, tongue enlargement
What are the physiologic effects of hypothyroidism?
Bradycardia, decreased CO, hypotension, SOB secondary to effusions
What are the diagnositic hallmarks of hypothyroidism?
H+P, decreased T3/T4, increased TSH in primary hypothyroidism, decreased TSH in secondary hypothyroidism, thyroid autoantibodies, low hematocrit, decreased voltage or inverted T waves on ECG.
What is the treatment for hypothyroidism?
Thyroxine PO, or IV emergently if patient presents in myxedema coma.
What is myxedema coma?
A state of decompensated hypothyroidism. Lab values can be similar to general hypothyroidism, but is stimulated by a stressful event (MI, stroke, drugs, etc). Primary symptoms include altered mental status and hypothermia. Can also present with hypoglycemia, hypotension, hyponatremia, hypercapnia, hypoxia, bradycardia, and hypoventilation.
What are the three most common causative organisms of thyroiditis?
Strep pyogenes, staph aureus, pneumococcus pneumoniae
What are the major risk factors for development of thyroiditis?
Female sex, goiter, thyroglossal duct
What are the signs and symptoms of thyroiditis?
Unilateral neck pain and fever, euthyroid state, dysphagia
What is the treatment for thyroiditis?
IV antibiotics and surgical drainage
What is De Quervain thyroiditis?
Also known as Subacute thyroiditis, it is typically a self limited, non-infectious thyroiditis.
What is the etiology of subacute thyroiditis?
Post-viral URI. Possibly secondary to immune mimicry.
What percentage of patients with subacute thyroiditis become permanently hypothyroid?
10%
What are the common signs and symptoms of subacute thyroiditis?
Fatigue, depression, neck pain, fever, unilateral swelling of thyroid with overlying erythema, firm and tender thyroid, transient hyperthyroidism usually preceding hypothyroid phase
What is the treatment for subacute thyroiditis?
Conservative management. Typically goes away within 6 weeks. Can manage pain with NSAIDs.
What are the major risk factors for developing Hashimoto’s thyroiditis?
Down’s syndrome, Turner syndrome, familial Alzheimer’s disease, history of radiation therapy as child
What are the common signs and symptoms of Hashimoto’s thyroiditis?
Painless enlargement of thyroid, neck tightness, presence of other autoimmune diseases.
What are the common lab findings in Hashimoto’s thyroiditis?
Circulating antibodies against microsomal thyroid cells, thyroid hormone, T3, T4, or TSH receptor.
What is seen on pathology in Hashimoto’s thyroiditis?
Firm, symmetrical, enlargemen; follicular and Hurthle cell hyperplasia; lymphocytic and plasma cell infiltrates
What is the treatment for Hashimoto’s thyroiditis?
Thyroid hormone is first choice. If refractory to medical therapy, partial thyroidectomy is indicated.
What is Riedel’s fibrosing thyroiditis?
A rare disorder in which fibrosis replaces both lobes and the isthmus of the thyroid.
What conditions is Reidel’s thyroiditis associated with?
Other fibrosing conditions such as retroperitoneal fibrosis, and sclerosing cholangitis.
What are the signs and symptoms of Riedel’s thyroiditis?
Euthyroid, neck pain, possible airway compromise, firm, nontender, enlarged thyroid.
How can one diagnose Riedel’s thyroiditis?
Open biopsy is required to rule out carcinoma or lymphoma.
What is the treatment for Riedel’s thyroiditis?
If the airway is compromised, isthmectomy is indicated. Without airway compromise, medically treat with steroids.
What percentage of solitary thyroid nodules are malignant?
15%
What percentage of malignant thyroid nodules present as well differentiated cancers?
90-95%
What are concerning findings on exam for malignant thyroid disease?
Hard, fixed gland, and palpable cervical lymph nodes.
What are the signs and symptoms associated with malignant thyroid nodules?
History of previous head or neck irradiation, family history, age, gender, sudden enlargement of a nodule, compressive complaints.
What is the false positive rate of FNA of a thyroid nodule?
1%
What is the false-negative rate of FNA of a thyroid nodule?
5%
What is the diagnostic modality of choice for thyroid nodules?
FNA
What are the common findings on FNA for a thyroid nodule?
Benign (65%), Suspicious (15%), Malignant (5%), Nondiagnostic (15%).
What is the treatment for a benign thyroid nodule?
US for sizing. Check initial thyroglobulin and then follow over time.
What is the diagnostic algorithm for a suspicious thyroid nodule on FNA?
Obtain I-123 scan: 85% will be cold nodules with a 10-25% chance of being malignant. 5% are hot nodules with a 1% chance of malignancy.
Surgery is indicated if serial T4 levels do not regress and biopsy is worrisome.
What is the treatment for a malignant thyroid nodule on FNA?
Surgery.
What is the treatment for a biopsy proven cyst of the thyroid.
Drain completely (curative in 75% of cases). If larger than 4 cm, complex, or recurrent after 3 drainage attempts, then evaluate for surgery.
What percent of thyroid cancers are papillary?
80-85% in adults. 75% in children.
What percent of thyroid cancers are follicular?
5-10%
What percent of thyroid cancers are medullary?
5-10%
What percent of thyroid cancers are anaplastic?
1%
What is the typical demographic distribution of papillary thyroid cancer?
age 20-40, 2:1 F:M, Hx of radiation
What is the typical demographic distribution of follicular thyroid cancer?
50s, 3:1 F:M, in dyshormonognesis
What is the typical demographic distribution of medullary thyroid cancer?
50-60, 1.5-1:a F:M, Associated with MEN
What is the typical demographic distribution of anaplastic thyroid cancer?
60-70s, 1.5/1 F:M, well-differentiated prior thyroid cancer and iodine deficient.
How can you diagnose papillary thyroid cacner?
FNA and CT or MRI
How can you diagnose follicular thyroid cancer?
FNA and CT or MRI
How can you diagnose medullary thyroid cacner?
FNA, presence of amyloid is diagnostic, and can check immunohistochemistry for calcitonin
How can you diagnose anaplastic thyroid cancer?
FNA
What are the gross characteristics of papillary thyroid cancer?
Intrathyroidal, partially encapsulated, likely to be multifocal, hard, white, areas of necrosis, cystic changes
What are the gross characteristics of follicular thyroid cancer?
Encapsulated tumor, solitary
What are the gross characteristics of medullary thyroid cancer?
Unilateral, mid-upper lobes, familiar tumors are more likely to be multicentric and bilateral
What are the gross characteristics of anaplastic thyroid cancer?
Macroinvasion, clinically perceptible as are regional lymph nodes
What are the histologic characteristics of papillary thyroid cancer?
Papillary projections; pale, abundant cytoplasm; psammoma bodies; Orphan Annie eyes
Describe psammoma bodies. Where are they typically found?
Psammoma bodies are a round collection of calcium. They typically have a laminar appearance, are circular, acellular, and basophilic. They are associated with papillary histomorphology, and are thought to arise from infarction and calcification of the papillary tips, or calcification of intralymphatic tumor thrombi. They are classically associated with papillary thyroid carcinoma, papillary renal cell carcinoma, ovarian papillary serous cystadenocarcinoma, endometrial adenocarcinomas, meningiomas, peritoneal and pleural mesotheliomas, somatostatinomas, and prolactinomas.
What are orphan annie eyes, and where are they typically found?
They are nuclear inclusions in which the nuclei have uniform staining and appear empty. They are typical of papillary thyroid cacners.
What are the histologic characteristics of follicular thyroid cancers?
Solitary and encapsulated 90% of the time.
What are the histologic characteristics of medullary thyroid cancers?
They are of C-cell origin, appear as sheets of cells, stain positive for amyloid and collagen
What are the histologic characteristics of anaplastic thyroid cancers?
Sheets of heterogeneous cells.
What is the route of papillary thyroid cancer metastasis?
Lymphatic
What is the rout of follicular thyroid cancer metastasis?
Hematogenous
What is the route of medullary thyroid cancer metastasis?
- Lymphatic spread to local LNs in the neck and mediastinum.
- Local spread into the trachea and esophagus
What is the route of anaplastic thyroid cancer metastasis?
Aggressive local disease, with 50% of patients having synchronous pumonary metastasis at the time of diagnosis.
What is the treatment for papillary thyroid cancer?
For minimal cancers, lobectomy and isthmectomy are indicated. For more extensive disease total or near-total thyroidectomy are indicated. For LN+ disease modified radiacl neck dissection is indicated. I-131 ablation is appropriate in patients with residual thyroid tissue or LN+ metastasis
What is the treatment for follicular thyroid cacner?
For minimal cancers, lobectomy and isthmectomy are indicated. For more extensive disease total or near-total thyroidectomy are indicated. For LN+ disease modified radiacl neck dissection is indicated. I-131 ablation is appropriate in patients with residual thyroid tissue or LN+ metastasis
What is the treatment for medullary thyroid cancer?
For both sporadic and familial MTC, total thyroidectomy and central neck node dissection is indicated.
What is the treatment for anaplastic thyroid cancer?
- Debulking resection of thyroid and invaded structures
- External radiation therapy
- Doxorubibin-based chemotherapy
What is the prognosis for papillary thyroid cancer?
10 year survival is 74-93%. Prognosis is worse in older patients and those with distant mets. Presence of +LNs is not strongly correlated with overal survival.
What is the prognosis for patients with medullary thyroid cancer?
10 year survival is 70%. Worse in older patients, distant mets, >4cm, and high tumor grade. +LNs are not strongly correlated with overall survival.
What is the prognosis for patients with anaplastic thyroid cancer?
Very poor. Shortest survival time of all tumors from time of diagnosis. Median survival is 14 weeks from initial presentation
What are the variants of papillary thyroid cancer?
Sclerosis variant presents with +LN 100% of the time.
What are the variants of follicular thyroid cancer?
Hurthle cell tumors present as bilateral, multifocal tumors with spread to regional LN.
What is the treatment for Hurthle cell tumors of the thyroid?
Ipsilateral lobectomy, isthmectomy, and central neck dissection. If pathology comes back as carcinoma, total completion thyroidectomy is indicated.
What is the prognosis for medullary thyroid cancer?
10 year survival is 70-80%
