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228 Cards in this Set
- Front
- Back
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THYROID - BRILL - FRIDAY FEB 2
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at what day in utero does formation of the thyroid start, and what happens?
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day 24 - evagination of the tongue base - descends in the midline of the neck forming the thyroglossal duct
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what happens to the thyroglossal duct?
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involutes prior to birth
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what is the thyroid gland like morphologically?
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two lobes conneted by an isthmus
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what % have a pyramidal lobe?
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50%
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what things may be left along the course of descent of the thyroid gland (3)?
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1) aberrant thyroid gland; 2) ectopic thyroid tissue; 3) thyroglossal duct cysts/sinus tracts
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where may aberrant thyroid glands be (2)?
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1) lingual; 2) subhyoid
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what may happen to thyroglossal duct cysts/sinus tracts (2)?
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1) infection; 2) rarely cancer
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what other unusual thing can happen in development of the thyroid gland?
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excessive descent --> substernal thyroid
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PHYSIOLOGY
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what are lobes divided into, and what are these divisions composed of?
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thyroid gland is divided into lobules composed of follicles, where hormones are produced and stored
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besides T3 and T4, what hormone is produced in the thyroid, and where?
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parafollicular or C cells synthesize and secrete the hormone calcitonin
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what is the name of T3, and the name of T4?
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T3 - triiodothyronine; T4 - thyroxine
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by what process are T3 and T4 formed (what reaction on what molecule?
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post-transcriptional iodination of thyroglobulin
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at what specific location do iodination and coupling reactions occur?
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luminal cell membrane of follicular cells
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in what form is the hornome stored?
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as colloid
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in what form is most T3 and T4 in circulation?
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bound to plasma proteins (TBG, transthyretin, albumin, pre-albumin) for transport
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what type of receptors do T3 and T4 interact with, and what is the result?
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they interact with nuclear receptors in peripheral tissues --> increase in basal metabolic rate
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what is T3 and T4 formation controlled by, and where does it come from?
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T3, T4 formation controlled by TSH released from anterior pituitary in response to trophic factors from the hypothalamus
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how are TRH and TSH levels controlled?
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negative feedback from T3, T4
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GOITER
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what type of enlargement is a goiter, and what is it secondary to?
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hyperplastic enlargement of the thyroid secondary to impaired T3, T4 synthesis
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what does the impaired synthesis of T3, T4 lead to?
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increased TSH levels, which cause hypertrophy and hyperplasia of follicular cells
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what classes of goiters are there (2)?
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1) diffuse non-toxic (simple) goiter; 2) multinodular goiter
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what part of the gland does diffuse non-toxic goiter involve?
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all
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what are the two forms of diffuse non-toxic goiter, and which is more common (bold)?
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1) endemic; 2) sporadic
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when is simple goiter endemic?
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when it is present in more than 10% of the population
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what causes endemic goiter (2)?
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1) low levels of iodine in soil, water, diet; 2) goitrogens in diet
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what sex/age is most likely to get sporadic goiter?
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young adult female
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what causes it (2)?
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1) ingestion of substances that interfere with hormone synthesis; 2) hereditary enzymatic defects
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how are these defects inherited?
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autosomal recessive
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what is the goiter called, when it is hereditary?
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dyshormogenetic goiter
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in most cases, what is the cause of sporadic goiter?
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in most cases, cause not apparent
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what happens in multinodular goiter?
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recurrent hyperplasia and involution
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what does this lead to?
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irregular enlargement with nodules and cysts
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what happens secondary to rupture of cysts, follicles, and vesicles (3)?
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1) hemorrhage; 2) scarring; 3) calcifications
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what type of problems do goiters cause in the neck?
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mass effect compressing neck structures
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how do they relate to neoplasms?
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they can mask or mimic neoplasms
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how do most goiters affect hormone deficiency, and what is the term for this?
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most are euthyroid - the increase in mass overcomes hormone deficiency
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what problem happens in a minority of goiters related to hormone production and what is this called?
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Plummer's syndrome - a minority develop hyperfunctioning nodule, resulting in toxic multinodular goiter
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hwo does this syndrome differ from Graves disease?
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this syndrome does not have the skin and eye changes of Graves disease
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how often are goiters associated with hypothyroidism?
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rarely
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HYPERTHYROIDISM (THYROTOXICOSIS)
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what is the most common cause?
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hyperfunctioning of the gland
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what else can cause it (2)?
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1) ingestion of exogenous substances (Synthroid, iodide); 2) leakage of hormone from non-hyperactive gland
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what various organ systems does thyrotoxicosis affect (6)?
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1) cardiac; 2) neuromuscular; 3) dermatologic; 4) GI; 5) ocular; 6) skeletal
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what are the cardiac effects (5)?
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1) tachycardia; 2) palpitiations; 3) arrhythmias (A-fib); 4) cardiomegaly; 5) CHF
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what neuromuscular problems are caused by thyrotoxicosis (list - one bold term we definitely must know, plus others)?
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hyperreflexia, tremors, hyperactivity, anxiety, poor concentration, forgetfulness, insomnia, proximal muscle weakness, wasting
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what dermatologic problems are caused by thyrotoxicosis (list - one bold term we definitely must know, plus others)?
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heat intolerance, warm/moist/flushed skin with increased sweating, hyperpigmentation, acropathy (thick fingers and toes)
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where is there hyperpigmentation?
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over extensor surfaces
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what problems are caused in the gastrointestinal system (3)?
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1) increased gut motility; 2) increased appetite; 3) overeating
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what happens to weight?
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weight loss despite increased food intake
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what causes ocular problems?
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sympathetic overstimulation
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what pocular problems are caused (3)?
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1) wide, staring gaze; 2) lid lag
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what problems are caused in the skeleton (2)?
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1) osteoporosis; 2) increased fractures
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what is the most common cause of thyrotoxicosis, and what % of cases does this account for?
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diffuse toxic hyperplasia (Graves disease) - 85% of cases
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what are other common causes (2)?
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1) toxic multinodular goiter (Plummer's syndrome); 2) toxic adenoma
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what are what are three uncommon causes we must know?
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1) choriocarcinoma/hydatidiform mole (extrathyroidal uterine/ovarian neoplasms); 2) TSH-secreting pituitary adenoma (rare); 3) struma ovarii (ovarian teratoma with ectopic thyroid)
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how can neonates get thyrotoxicosis?
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associated with maternal graves disease
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can thyroiditis and/or thyroid carcinoma cause thyrotoxicosis?
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yes
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what does primary thyrotoxicosis mean?
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abnormality of gland itself
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what drugs can be used to treat thyrotoxicosis (4)?
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1) beta blockers; 2) propylthiouracil; 3) methimazole; 4) iodide (paradoxically)
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what other treatments can be used (2)?
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1) radioiodine ablation; 2) surgery
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GRAVES DISEASE
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what type of disorder is Graves disease?
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autoimmune
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what three things does it induce?
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1) thyrotoxicosis with diffuse hyperplasia of gland; 2) ophthalmopathy; 3) sometimes dermopathy
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why is the eye pushed forward (3)?
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1) fatty infiltration; 2) deposition of hydrophilic mucopolysaccharides; 3) periorbital edema
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why is there lid retraction?
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swollen and fibrotic extraocular muscles
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what does incomplete closure of the eye lead to (2)?
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1) keratitis; 2) corneal ulceration
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what can happen to the optic nerve?
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compression
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what type of immune reaction is Graves disease mediated by?
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T cell mediated autoimmune phenomenon - immune reaction against thyroid follicular antigens that are also found in retro-orbital space
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what is the dermopathy termed, and where doesit generally occur?
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usually occurs ove shins or feet, and is termed "pretibial myxedema"
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why is pretibial myxedema a confusing term?
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because myxedema is usually associated with hypothyroidism
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what happens to the skin, and why?
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becomes thickened and indurated because of thickening of the dermis by deposition of glycosaminoglycas and ilymphocyte infiltration
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what problems are unique to Graves disease (3)?
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1) diffuse hyperplasia; 2) ophthalmopathy; 3) dermopathy
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what is the female to male ratio in Graves disease?
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7 to 1
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what HLA alleles is Graves disease associated with (2)?
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1) B-8; 2) DR-3
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what etiological agent is found in the serum of patients with Graves disease (name and what they are)?
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TSI - thyroid stimulating immunoglobulin - they are IgG immunoglobulins that bind to TSH receptors, stimulate adenyl cyclase activity, and increase release of thyroid hormonses
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what are the possible courses of symptoms (2)?
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1) wax and wane; 2) lead to thyroid storm (medical emergency if untreated)
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what are drugs used for thyrotoxicosis (2)?
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1) propylthiouracil; 2) methimazole
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what are other treatments (2)?
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1) radioiodine; 2) surgery
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HYPOTHYROIDISM
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what are the three classes of hypothyroidism?
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1) primary (gland); 2) secondary (pituitary or hypothalamic); 3) tertiary/central (hypothalamic disease)
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what happens if hypothyroidism is present in infancy?
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cretinism
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what is this manifested by (5)?
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1) short stature; 2) retardation; 3) coarse facial features; 4) protruding tongue; 5) umbilical hernia
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what can be done about this?
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preventable if treated early
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what happens if thyroid deficiency occurs during early fetal development (3)?
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1) deaf-mutism; 2) spasticity; 3) severe mental retardation
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what can cause thyroid deficiency during early fetal development (3)?
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1) thyroid agenesis; 2) severe iodine lack; 3) congenital biosynthetic defect
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what is hypothyroidism termed in an older child or adult?
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myxedema
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what is the most characteristic sign of myxedema?
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cold intolerance
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what happens to reflexes?
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slowed
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where is hair lost, particularly?
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especially on the outer third of eyebrows
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what type of edema is there and where?
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peri-orbital, peripheral non-pitting edema
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what color does skin turn, and why?
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yellow, secondary to sluggish conversion of carotenes to vitamin A in the intestine
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what can happen to the voice?
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hoarseness
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what can happen to the GI system?
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constipation
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what can happen to the heart?
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cardiomyopathy
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what are other symptoms of myxedema (list)?
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fatigue, depression, lethargy, weight gain, low body temperature
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what can severe hypothyroidism cause?
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myxedema coma
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what is it characterized by (5)?
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1) loss of consciousness, ; 2) hypothermai; 3) hypoventilation; 4) sever bradycardia; 5) pericardial effusion
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what is it difficult to be distinguished from?
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addisonian crisis
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how may it be treated emergently?
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administer synthroid and cortisone
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what are the three classes of causes of hypothyroidism?
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1) insufficient thyroid parenchyma; 2) niterference with thyroid hormone synthesis; 3) suprathyroidal
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what are four causes of insufficient thyroid parenchyma?
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1) developmental; 2) surgical ablation; 3) radiation injury; 4) Hashimoto thyroiditis
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what are four causes of niterference with thyroid hormone synthesis?
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1) thyroid hormone resistance syndrome; 2) congenital biosynthetic defects (dyshormonogenetic goiter); 3) drugs; 4) autoimmune disorders
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how is thyroid hormone resistance syndrome inherited?
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autosomal dominant
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what drugs can cause interference with thyroid hormone synthesis (3 examples)?
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1) lithium; 2) iodides; 3) p-aminosalicylic acids
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what types of suprathyroidal causes are there (2)?
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1) pituitary lesions reducing TSH secretion; 2) hypothalamic lesions that reduce TRH delivery
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what is an example of a pituitary lesion that reduces TSH secretion?
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Sheehan's syndrome
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what is the most common cause of primary hypothyroidism, in iodine-sufficient areas of the world?
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Hashimoto's thyroidits
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THYROIDITIS
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what types of thyroiditis are there (5 main)?
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1) chronic autoimmune/Hashimoto's; 2) subacute granulomatous/DeQuervain thyroiditis; 3) subacute lymphocytic (painless) thyroiditis; 4) palpation thyroiditis; 5) Reidel's thyroiditis
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what is the female predominance of Hashimoto's thyroiditis?
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20 to 1
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what HLA alleles is Hashimoto's associated with (2)?
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1) DR-5; 2) DR-3
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what is the pathogenesis of Hashimoto's?
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sensitization of CD4+ T-helper cells to thyroid antigens
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what does this lead to (2) and what part of the thyroid is attacked?
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1) uncontrolled attack on follicular epithelium by cytotoxic T cells; 2) T-helper cell participation in B cell formation of autoantibodies
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what is the most important type of antibodies are present, and what do they do?
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TSH receptor antibodies are present that block the receptor
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what are other autoantibodies directed against (3)?
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1) thyroglobulin; 2) thyroid peroxidase; 3) iodine transporter
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what should be remembered about gland enlargement in Hashimoto's?
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it is painless
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what can form in Hashimoto's and what does this raise suspicion of?
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nodules can form, raising suspicion of neoplasm
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what particular cells are seen in histology in Hashimoto's, and what are they?
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Hurthle cells (follicle cells with abundant granular cytoplasm)
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what else are seen in histology (2)?
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1) lymphoplasmacytic infiltrates; 2) lymphoid follicles with germinal centers
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what happens to thyroid hormone levels in early stages of Hashimoto's, and why?
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transient thyrotoxicosis - follicles destroyed with release of hormone
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what happens later?
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hormones fall and hypothyroidism develops
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what are patients at an increased risk for developing (2)?
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1) B cell lymphomas; 2) other autoimmune diseases
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what does subacute (granulomatous, DeQuervain) thyroiditis often follow?
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upper respiratory viral infections (mumps, influenza, cocksakie, measles, others)
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what is the course of this disease?
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inflammation followed by period (2-8 weeks) of hypothyroidism, then complete recovery
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what is gland like?
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tender and enlarged, with pain on swallowing that radiates to upper neck, ears
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what other symptoms may be present?
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constitutional - malaise, anorexia, myalgia, fever
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what is seen on histology (2), and what do they resemble?
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aggregates of giant cells and macrophages, resembling granulomas
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what is the cause and time course of subacute lymphocytic (painless) thyroiditis?
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idiopathic, self-limited
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what may it present like (2)?
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1) symptomless; 2) thyrotoxicosis
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what may it progress to in a minority of cases?
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hypothyroidism
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who is subacute lymphocytic (painless) thyroiditis most common in?
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post-partum females
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is there a risk of recurrence?
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yes, following subsequent pregnancies
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what two things were said not to be commonly seen in subacute lymphocytic thyroiditis?
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1) fibrosis; 2) Hurthle cell metaplasia
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what is palpation thyroiditis like on histology?
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similar to subacute granulomatous
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what is the cause of palpation thyroiditis?
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vigorous palpation of the thyroid gland with mechanical disruption of follicles
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is there any abnormality in thyroid function in palpation thyroiditis?
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no
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what is Riedel's thyroiditis, and how common is it?
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rare form of fibrosing thyroiditis
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where does fibrosis occur?
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destructive fibrosis extends from thyroid to structures of the neck
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what is gland like?
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hard, painless gland
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what can this lead to (3)?
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1) laryngeal nerve paralysis; 2) shortness of breath; 3) difficulty swallowing
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what does this disease simulate?
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malignancy
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what may Riedel's thyroiditis be associated with?
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thyroiditis elsewhere in the body
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what can cause other thyroiditides (3)?
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1) fungi; 2) blood-borne bacteria; 3) pneumocystis carinii in immunocompromised patients
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NEOPLASMS
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how common are thyroid nodules, and what type are most (2)?
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very common - most are 1) non-neoplastic (goitorous); 2) benign neoplasms (follicular adenomas)
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what types of nodules are more likely to be neoplastic (3)?
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1) solitary nodules; 2) nodules in younger patient; 3) nodules in males
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what type of nodules are more likely to be benign?
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hot nodules - those that take up radioiodine
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what is associated with an increased risk of thyroid canceR?
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history of radiation
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what is the first diagnostic test performed on a thyroid nodule?
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fine needle aspiration (rapid, relatively non-invasive, inexpensive)
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what is the most common neoplasm?
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follicular adenoma
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what is it like (number, benign/malignant, encapsulation)?
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benign, solitary, encapsulated
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what is it like on radionuclide scanning?
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cold
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what problem may is cause, rarely?
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rarely hyperfunctional - toxic adenomas independent of TSH
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THYROID MALIGNANCIES
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what % of carcinomas are thyroid cancers?
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1.50%
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what chromosomal rearrangements are said to be behind papillary carcinomas (2)?
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1) RAS; 2) NTR k1
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what forms of thyroid cancer are there (5)?
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1) papillary carcinoma; 2) follicular carcinoma; 3) Hurthle cell neoplasm; 4) medullary carcinomas; 5) anaplastic carcinomas
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what activating mutations are behind papillary carcinomas (2)?
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1) BRAF; 2) RAS
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what nuclear changes are behind follicular carcinomas?
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1) RAS mutations; 2) PAX8-PPAR-gamma-1 fusion
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what mutations are behind medullary carcinomas?
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RET mutations
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what mutations are behind anaplastic carcinoma?
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inactivating point mutations in p53 suppressor gene
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what is the most common form of thyroid cancer, what % of cancers does it account for, and who does it occur in (age, situation)?
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papillary carcinoma - 75 to 85% of cases - most common in ages 20 to 40 and in patients with previous radiation exposure
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is it encapsulated?
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can be either encapsulated or infiltrating
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what does it appear like histologically (shape of papillae, and other feature of them)?
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complex branching papillae with fibrovascular cores
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what do nuclei look like (3 features)?
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1) optically clear "Little Orphan Annie Eye" nuclei; 2) intranuclear inclusions; 3) nuclear grooves
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what other structures are seen in paplillary carcinoma (name and composition)?
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psammoma bodies (concentrically calcified structures)
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where do papillary carcinomas metastasize to?
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regional lymph nodes
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what type of growth do most papillary carcinomas exhibit, and what is the overall 10 year survival?
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most exhibit indolent growth, and the overall ten year survival is over 95% - but prognosis depends on age and state of the disease
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what variant of papillary carcinoma occurs that is more aggressive, and who does it occur in?
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tall cell variant occurs in older patients, and is very aggressive
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who is the prognosis best in?
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children and young adults
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what is the general treatment?
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total thyroidectomy followed by radioiodine therapy
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what is the second most common form of thyroid carcinoma, and what % of cases does it account for?
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follicluar carcinoma - 10 to 20% of cases
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what do lesions look like, and what are they difficult to distinguish from?
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well-differentiated, encapsulated lesions are difficult to distinguish from follicular adenomas
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what is the histologic criteria for follicular carcinoma (2 things it must invade)?
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1) invasion of capsule/surrounding parenchyma; 2) vascular invasion (vessels in or beyond capsule)
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where does follicular carcinoma metastasize to?
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hematogenously, to bone, lungs, and brain
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what is the treatment for follicular carcinoma?
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total thyroidectomy followed by radioiodine therapy
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what do Hurthle cell carcinomas behave like?
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the same as non-Hurthle cell follicular adenomas and carcinomas - they are diagnosed using the same criteria (capsular and vascular invasion) as well
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what are Hurthle cells like (what cells do they come from, and what do they look like)?
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follicular cells with abundant granular cytoplasm
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what % of thyroid carcinomas are medullary carcinomas, and what are they derived from?
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5% - they are derived from parafollicular cells or C cells
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what do these cells secrete?
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calcitonin
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in what setting do 20% of the cases occur in (3)?
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1) MEN IIA; 2) MEN IIB; 3) familial tumors without associated MEN syndrome - most cases, though, are sporadic
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what else occurs in MEN IIA (3)?
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1) parathyroid hyperplasia; 2) parathyroid adenomas; 3) pheochromocytoma
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what else occurs in MEN IIB (4)?
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1) parathyroid hyperplasia; 2) pheochromocytoma; 3) Marfanoid habitus; 4) mucocutaneous ganglioneuromas
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what type of mutations are seen in MEN IIA and MEN IIB syndrome?
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germline mutations in RET proto-oncogene
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what mutations are seen in nonfamilial (sporadic) medullary carcinomas?
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RET mutations
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are sporadic cases more likely in younger or older patients?
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sporadic - older patients; MEN II - younger
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what are cells like histologically in medullary carcinoma (2 possible shapes, something seen inside)?
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rounded or spindled, with stippled chromatin
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are medullary tumors encapsulated?
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no
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what other feature is seen in medullary carcinomas, histologically, and what is it compsed of/derived from?
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amyloid tumor stroma (calcitonin derived)
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what happens to this stroma when polarized?
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it is CongoRed positive with apple-green birefringence when polarized
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in what way unique to thyroid cancer may medullary carcinoma present?
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paraneoplastic syndrome
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what may these tumors release (4)?
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1) CEA; 2) somatostatin; 3) serotonin; 4) vasoactive intestinal peptide
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what are calcitonon and calcium levels like?
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although calcitonin is elevated, hypocalcemia is not a prominent feature
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what can MEN associated cases be masked by?
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clinical manifestations from associated parathyroid lesion or pheochromocytoma
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what should relatives of patients with medullary thyroid carcinoma be screened for (2)?
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1) elevated calcitonin levels due to C cell hyperplasia; 2) RET mutation
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what is a major precursor to medullary carcinoma in MEN IIA, and what is indicated?
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C cell hyperplasia - thyroidectomy is indicated
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what can serve as a good tumor marker for medullary thyroid cancer?
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calcitonin
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which types of medullary CA are aggressive tumors (2) and what is the five year survival rate?
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1) those associated with MEN IIB; 2) sporadic cases - these are both aggressive with a 5 year survival rate of 50%
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what medullary carcinomas are often indolent?
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familial medullary carcinomas that are not associated with MEN
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where do medullary carcinomas metastasize?
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through bloodstream (bone, liver, lung) or to lymph nodes
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what is the treatment for medullary carcinoma?
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surgical excision and not radioactive iodine, as C cells are neuroendocrine cells and do not have iodine transport
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what % of thyroid carcinomas are anaplastic carcinomas?
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<5%
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what do they look like histologically?
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undifferentiated neoplasms
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who do they occur in, and what is the progression and prognosis?
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occur in the elderly, are large locally invasive rapidly growing neck masses that are uniformally fatal with no effective therapy
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what is survival after diagnosis?
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less than one year
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what features are seen in dedifferentiated tumors (2)?
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1) loss of I131 uptake; 2) decreased synthesis of thyroglobulin
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how common are sarcomas in the thyroid?
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rare
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what other type of malignancies are common in patients with history of Hashimoto thyroiditis?
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lymphomas - particularly non-Hodgkins B cell lymphomas
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