Endocrine Clinical Module Summary Notes- Lucy

endocrine imaging is restricted to which glands?`

thyroid, parathyroid, adrenals

endocrine glands (tissues)

secrete hormones into the blood steam which stimulate, affect, or control the metabolism of bodily cells and tissues, complementary control system to the nervous system

what is the function of the anterior pituitary gland?

produces and secretes hormones that oversee the fxn of the thyroid, gonads, and adrenal cortices, stimulates protein anabolism and cell growth, milk production, and pigmentation of the skin

what is the function of the posterior pituitary gland?

stores hormones specifically oxytocin and ADH (vasopressin)

adult thyroid weight

15-25 g

thyroid shape and size

right lobe larger than left and extends further in superior and inferior directions, lobes connected by a narrow midline of thyroid tissue (ishtmus), pyramidal lobe variant

ectopic sites of thyroid tissue

lingual, substernal, struma ovarii

what two major circulatng products of the thyroid does the hypothalamus monitor?

T3, T4

what happens when the hypothalamus detects T3/ T4 levels are too low?

hypothalamus secretes TRH, stimulating the release of TSH from anterior pituitary, TSH travels through blood to the thyroid and instructs it to produce and release more T3/T4

what is needed for the thyroid to produce T3 and T4 hormones?

iodine

how is dietary iodine absorbed?

reduced in the upper intestine to iodide, absorbed with 90% efficiency entering circulation w/in 1 hour of teaching bowel, blood stream circulates iodide until it is taken up by the thyroid or excreted by kidneys

where are T3 and T4 stored after production?

on thyroglobulin molecules present in the follicles of the thyroid

what happens when TSH is released by the anterior pituitary?

TSH travels to the thyroid through the blood and binds to the cell membrane of the follicle cells

how do T3 and T4 leave the follicles?

T3 and T4 separate from the thyroglobulin, pass through the cell membranes of the cuboidal epithelia that make up follicle walls thereby entering the bloodstream

where are T3 and T4 found in the blood stream?

T3 and T4 are bound to thyroid binding globulin, albumin, and thyroid binding prealbumin

how is most of the T3 in the bloodstream formed?

monodeiodination of T4 by peripheral tissues rather than produced by the thyroid

clearance half time for T4

6 days

clearance half time for T3

1 day, more biologically active than T4

Tc99m pertechnetate is trapped by the gland but is not ___________ , therefore it does not become part of ____________________________;

organified, any thyroid hormones

administed dose of intravenous Tc99m pertechnetate

1-10m mCi

radiation dose to thyroid gland caused by Tc99m pertecnetate

1-2 rads

critical organ for Tc99m pertechnetate

stomach wall & thyroid

administered dose of oral I-123

300 uCI

radiation dose to thyroid gland caused by I-123

4 rads

critical organ for iodine agents

thyroid

administered dose of oral I-131

50-100 uCi.

radiation dose to thyroid gland caused by I-131

65-130 rads for scan, 7 rads for uptake

administered dose of oral I-125

50-100 uCi

radiation dose to thyroid gland caused by I-125

40-80 rads

I-123

cyclotron produced, gamma decay at 159 keV, 13 hour half life

I-131

decays by beta 190 keV and gamma emission 364 keV, obtained from fission of U235 or via reactor, can be used for uptakes, imaging, or therapy, significant absorbed dose

I-125

reactor produced agent, gamma decay 60 keV, poor imaging agent, 60 day half life causes high radiation dose

Tl 201

proposed for WB studies in patients who have thyroid cancer, patient can remain on meds while being scanned as distribution is not suppressed by them

thyroid uptake

indicates the rate at which the thyroid picks up, traps, and organifies iodine using a NaI (Tl) probe with a flat field collimator centered over the thyroid, 25-30 cm from the crystal face, counts taken at 4, and 24 hours post admin of I-131, counts are compared with I-131 standard, can be done using TcO4 if necessary

average 24 hour percentage uptake

12-25%

perchlorate washout test

used to assess patients suspected of having an organification defect, congenital deficiencies of Hashimoto's thyroiditis are common, 20 uCi of I-131, 1g potassium chlorate orally, uptake every 15 minutes for 90 minutes following perchlorate administration

T3 suppression test

useful in assessing patients with borderline hyperthyroidism

TSH stimulation test

used to verify the glands ability to respond to TSH, patients with hyperthyroidism may be suffering from problems with their thyroids, pituitaries, hypothalami, diet, or medications, determines whether a patients failure is sited in the thyroid

Tc99m pertechnetate study

IV dose 4mCi, imaging 20 minutes post inj, pinhole collimator, anterior and 30 degree left and right anterior oblique views are obtained, palpable nodules should be marked and indicated on the images by radioactive markers, not used for substernal thyroid

I-123 study

300 uCi administered orally, images obtained b/w 4 and 24 hours, anterior and 30 degree left and right anterior oblique views, can be used for substernal thyroids

normal scan apperance

homogenous uptake, regular glandular borders, right lobe may be larger than left, lateral margins of gland straight or convex, concave margins indicate presence of internal or external masses

causes of non-visualization of thyroid gland

low uptake of the radiopharmaceutical, recent contrast studies, antithyroid drugs, certain medications, increased iodine pool, ectopic thyroid, high iodine diet

causes of cold nodules

adenomas, adenomatous hyperplasia, colloid cysts, primary thyroid carcinomas, hematomas, thyroiditis, fibrosis, extrinsic mass pressing on thyroid

acute thyroiditis

unusual, generally the result of bacterial infection, characterized by pain, tender hot, enlarged gland, fever and chills, normal thyroxine levels and normal or low iodine uptake value

subacute thyroiditis/ deQuervain's thyroiditis

unknown cause, similar symptoms to acute but also associate with thyrotoxicosis, , increased thyroxine level, low uptake, poor or absent visualization of the gland on images, damage to follicles

Chronic thyroiditis (Hashimoto's disease)

females 30-60 yrs, palpation reveals normal size, but hard adn firm gland which had become bound to surrounding muscles and underlying trachea as a result of being chronically inflamed, symptoms include dyspnea, dysphagia, hoarseness, alterations to respiratory sounds

hashimoto's thyroiditis

autoimmune thyroiditis consistent with other autoimmune diseases, gland is invaded by lymphocytes and starts to fibrose, then undergoes enlargement, typical among females 30-50 yrs, hypothyroidism steadily increases, disease interferes with organification step of hormone production

graves disease

autoimmune disease where antibodies bind to TSH receptors on cells of the thyroid, gland hypertrophies and increases synthesis and secretion of the thyroid hormones, typical of females 20-40

symptoms of graves disease

bulging eyes, scaly skin, and clubbing of the ends of the fingers, increased nervousness, warm/ hot skin, weight loss, diarrhea, heat intolerance, increased perspiration

treatments for graves disease

antithyroid drugs, surgery, I-131 therapy

I-131 therapy

beta/ gamma rays, effective half life in follicles of 3-5 days, allowing particle emissions to deliver an intense localized dose of radiation to the thyroid, mostly from 606 keV beta particles

I-131 therapy contraindications

pregnancy, breastfeeding

plummer's disease/ multinodular goiter

due to iodine deficiency or genetic, enlarged thyroid, becomes hyperthyroid, progresses to thyrotoxicosis, images present multiple hot and cold nodules, requires higher I-131 dose due to greater resistance to radiation

how are thyroid cancer metastases detected?

following thyroidectomy, patient is placed on T3 for a month then taken off, given a larger oral dose of I-131 (2-10 mCi), WB images taken 2-3 days after

normal iodine distribution

salivary glands, GI tract, kidneys, bladder, potentially liver

why is thyroid ablation important for destroying remaining thyroid tissue?

mets/ recurrence are much more likely to be detected if iodine cannot get trapped in thyroid tissue

parathyroid function

synthesize, store, and secrete parathormone (PTH) which helps to regulate calcium/ phosphorous levels in the blood, increase osteoclasis, decrease calcium excretion by kidneys, increase absorption of calcium by small intestines

primary hyperparathyroidism

females 40-70 yrs, most have single adenoma, the rest have parathyroid hyperplasia, or multiple adenoma

parathyroid adenoma

usually benign tumors with well developed capsules, demonstrate increased uptake of the agent in both immediate and delay images, delays more clear

parathyroid imaging

10-20 mCi of sestamibi injected IV and images taken over neck and chest 15 minutes post inj, repeat views ar 2-4 hours

adrenal cortices

endocrine component of adrenal gland, accounts for 90% of the mass, produces wide range of steroid hormones derived from cholesterol

cushing's disease

results from excess levels of glucocorticoids caused by excessive stimulation from ACTH or similar substances or autonomous adrenal function

cushing's disease symptoms

hypertension, diabetes, central obesity, thick/ coarse hair growth, flushed face, emotional outbursts, osteoporosis, subcutaneous stretch marks, round moon face, buffalo hump, pendulous abdomen, wasting of muscles

addison's disease

adrenals fail to produce sufficient amounts of glucocorticoids and mineralcorticoids

addison's disease symptoms

mental lethargy, nausea, vomiting, weight loss, anorexia, low BS, generalized weakness, elevated ACTH levels

pheochromocytoma

neuroectodermal tumors which arise from chromaffin cells of the sympathetic components of adrenals, 90% located in adrenal medullae, also found in sympathetic chains from skull to bladder

pheochromocytoma symptoms

excessive production of catecholamines causing headache, hypertension, palpitations, hyperhydrosis

diagnosis of pheochromocytoma

measure urinary or serum levels of catecholamines with imaging performed to localize site of tumor for removal

adrenal medulla is made up of

chromaffin cells- produce catecholamine hormones

131-I-MIBG

localizes in sympathetic tissues and pheochromocytomas, block thyroid for 1 day then admin 0.5 mCi by slow IV inj, image A/P abdomen, thorax, and pelvis at 24, 48, and 73 hours post inj, use markers to indicate position of axillae, lower rib, iliac crest

normal distribution of MIBG

liver, spleen, bladder, larger bowle, salivary glands, and heart

abnormal site of MIBG uptake

adrenal region

MIBG may accumulate in (tumors):1

neuroblastomas, carcinoids, paragnagliomas, pheochromocytomas

I 125 half life

60 days, associated wiht in vitro studies

I 131 emissions

beta and gamma, 8 day half life

why is imaging with I-131 a problem?

high energy mean smajor septal penetration problems with collimators, low administered dose causes poor count rates

I-123

13 hour half life, gamma emmission, cyclotron produces, good images, low radiation dose, allows for repeat studies

thyroif uptake can be performed using...

I-123, I-131, Tc99m

when should counts be taken for a thyroid uptake scan?

4-6 hours, 24 hours, can be done as early as 2 hours for hyper patients

thyroid uptake pt prep

off thyroid meds, low iodine diet, no recent contrast studies or other NM studies

what is a perchlorate washout test used for?

to assess patients who have an inability to adequately organify iodine due to a lack of peroxidase

why would a TSH stimulation test be performed?

to determine if hypothyroidism is primary (thyroid related) or secondary (pituitary)

what is a T3 suppression test used to evaluate?

hyperthyroidism

causes of hypothyroidsims

iodine deficiency, inherited enzyme deficiency, post-Rx, burned out goiter, mets in teh gland, thyroiditis, chronic thyroiditis, iodine excess/ saturation, pituitary/ hypothalamic disease

causes of hyperthyroidism

over-stimulation by the pituitary/ hypothalamus, medication, toxic nodular goiter/ plummers, graves

thyroid scan views and collimator

pinhole used to get 100k anterior then LAO and RAO to time, additional views take for palpable nodules

Which radiopharmaceutical is not suitable for imaging substernal thyroids due to mediastinal activity and bkg?

Tc99m

normal thyroid images

homogenous uptake, left lobe may be smaller than rightk may demonstrate pyramidal lober on upper isthmus, later margins straight or convex NOT concave

what may be seen in a thyroid image when using pertechnetate?

esophageal activity , clear with glass of water

cold nodules

adenomas, cysts, primary thyroid cancer, hematomas, extrinsic masses

malignancy is more likely

in males, if the nodule gets larger over time when patient is on suppression, pt has a history or neck irradiation

malignancy is less likely

if nodule involves entire lobe, is large and soft with smooth borders, is peripheral

MULTIPLE cold nodules may be due to

multinodular goiter, post irradiation and/ or neoplasm