NM 4203 Section 3

Endocrine System

Endocrine System Elaboration of hormones

– Pituitary Gland– Thyroid Gland– Parathyroid Gland– Islet cells of the pancreas– Adrenal Glands– Gonads (ovaries & testes)

Pituitary GlandPea sized gland at the base of the

midbrain

Anterior Pituitary– Consists of 2 cell

types: acidophils and basophils

– Basophil cells elaborate polypeptide hormones: TSH, ACTH, FSH, LH,ICSH

Posterior Pituitary– Vasopressin (ADH) – Oxytocin

Octreoscan In 111 – DTPA Pentetreotide Became available in U.S. in 1994 Adult Dose 6.0 mCi Usually SPECT scan at 24hrs.

Able to image the pituitary gland tumors arising from the pituitary gland.

Based on increased amounts of somatostatin receptors in the anterior pituitary.

Understanding the Lab Results

Why does a LOW TSH level indicate Hyperthyroidism?

Elevated levels of target gland hormone (Thyroid T4) , causes pituitary secretion of stimulating hormone (TSH) to be suppressed

Thyroid Gland Butterfly shaped Embryonic decent into the neck –

sometimes leaves midline tissue arising from the isthmus, called pyramidal lobe.

Secretes thyroid hormones thyroxine (T4) and triiodothyronine (T3)

Thyroid hormone synthesis depends on trapping and organification of iodine.

Hyperthyroidism TSH is low Thyroid hormone thyroxine (T4) is high

The elevation of thyroxine can be due to Grave’s Disease, autonomous nodule function, or ingestion of replacement T4

Hypothyroidism T4 is low (usually due to primary failure of thyroid

gland) TSH level is elevated (pituitary gland is trying to

compensate for the low T4 and tell the thyroid to produce more)

Low T4 and Low TSH: hypothyroid secondary to hypothalamic or pituitary disease.

May feel cold, tired and even depressed. May gain weight, even though eating less.

Proper evaluation of the thyroid should look at :

Clinical examLab resultsNuclear Medicine uptake/scan

Symptoms of Hyperthyroidism (thyrotoxicosis)

Increased appetite Weight loss Poor sleep / fatigue Muscle weakness Gastrointestinal problems Warm feeling/ sweating Tremors Nervous feeling Tachycardia

Graves’ Disease Thought to be autoimmune disease Enlarged thyroid Some patients will have swelling in

muscles around the eye, causing eye prominence, discomfort or double vision.

Uniform distribution of increased activity throughout the thyroid gland.

Multinodular Goiter Enlarged gland, usually causing

hyperthyroidism, with multiple cold and hot nodules. Patchy appearance.

Most frequent in middle-aged women Much less likely to be cancer than a

single cold nodule

Plummer’s Disease Toxic Nodule Can give uptake values that

are high, normal or only mildly elevated.

Resistant to radioactive iodine therapy and frequently requires doses 2-3 times higher than diffuse toxic goiter

Normal or borderline elevated uptake cannot be used to exclude hyperthyroidism

Subacute Thyroiditis Rapid onset of symptoms of hyperthyroidism Elevated T3 and T4

Low TSH Very low uptake Painful, swollen gland Little or no activity on the 99mTc scan or I 123 scan

Usually heals itself over a few months. NOT appropriate to treat these patients with

radioactive iodine

Hashimoto’s Thyroiditis

Chronic thyroiditis – most common thyroid disease in the U.S.

Thought to be autoimmune disease Inherited, and much more common in women Immune cells damage thyroid cells & compromise

their ability to make thyroid hormone. Will eventually cause hypothyroidism and a goiter. Fatigue, drowsiness, forgetfulness, brittle hair, itchy

skin, constipation, and weight gain.

Primary Hypothyroidism

Thyroid gland fails to synthesize and release thyroid hormone

Unless TSH stimulation is controlled (by hormone replacement therapy) , the thyroid gland will continue to grow.

Thyroid Cancer Papillary, follicular, medullary and anaplastic.

Majority are papillary and follicular – these are the only two that are treatable with radioiodine.

Tumors are seen as cold nodules. 80-90% are papillary – twice as often in females Almost always seen as a cold, solitary nodule

Thyroglobulin levels are a good method to monitor patients for recurrence after thyroidectomy and ablation.

Facts About 14,000 new thyroid cancer

cases in the U.S. each year Women account for 77% of new cases Five-year survival rate is over 90%

Hormone Synthesis Iodides are actively transported into

the thyroid gland, called “trapping” Iodide then goes through

“organification”

99mTc is “trapped” , but not “organified”. It slowly washes from the thyroid gland.

RadionuclidesI 131

Half – life 8.1 days 364 keV gamma emission Beta Decay (useful for therapy)

Uptake : – 5 – 10 uCi oral dose– Most accurate at 24 hrs.

RadionuclidesI 123

Half – life 13.3 hours 159 keV gamma emission (good for imaging)

Limited by expense and availability No beta emission (less dose to thyroid)

Scanning:– 300 – 400 uCi oral dose– Imaging is best at 3-4 hrs. * one source *

Radionuclides99mTC

Great for imaging Ionic charge and size allow 99mTc to be

trapped and concentrated in the thyroid. NOT organified (can’t be used for uptake)

Scan:– No prior patient prep– 4 - 15 mCi I.V. dose– Images done 15 – 20 minutes after injection

Thyroid Uptake Value is effected by total iodine intake. Uptake will be higher in a patient with

low – iodine diet. Uptake will be lower in a patient with

high iodine diet. (supplements, medications, seafood)

Thyroid Uptake Some additional considerations:

– Each facility must determine their own range of “normal”

– Good renal function is essential for a normal uptake.

Renal failure will result in low uptake

– Large meals before or after oral dose can decrease absorption and lower uptake.

Thyroid Uptake TSH level is used to diagnose hyper or

hypothyroid. Uptake is used to differentiate Graves’

disease from subacute thyroiditis or factitious hyperthyroidism.

Uptake determines whether or not the thyroid will take up iodine and how much (VERY useful for determining therapy)

Thyroid Uptake

% Thyroid uptake =

Neck counts – Thigh counts

/ Counts in standard X 100%

Thyroid Scan Pinhole collimator

– Should be used at the same distance on each patient

Anterior, LAO, RAO is standard and sternal notch should be identified.

Cold Nodules (nonfunctioning)

Most commonly a colloid cyst Most are benign: 20 – 30 % are

malignant Even in multinodular goiter, 10% of

dominant cold nodules are malignant. Warrant further investigation (biopsy)

Hot Nodule Most represent hyperfunctioning

adenoma Most are benign Can sometimes produce enough

thyroid hormone to inhibit pituitary secretion of TSH

Total Thyroidectomy from Thyroid Cancer

Whole Body I 131 imaging determines if there is residual tissue or metastases.

TSH should be elevated (over 50 uU/Ml is optimal)

– Not taking thyroid replacement hormones or injection of Thyrogen

– Failure of the TSH to rise could mean there is a significant amount of functioning thyroid tissue left after surgery.

I 131 Whole Body Imaging

Ranges from 1 to 10 mCi A recent study showed that whole body I131

imaging is not as sensitive as TSH thyroglobulin level for recurrent metastatic thyroid cancer. ??

I 123 has also been used for whole body imaging to determine mets.

I 131 Therapy for hyperthyroidism

“simple, safe, effective, inexpensive” Alternatives are antithyroid medication

and surgery. Toxic multinodular goiter and a solitary

toxic nodule is more resistant to I 131

Metastatic thyroid cancer

I 131 Ablation for Thyroid Cancer

Normal and malignant tissue is ablated 75 – 100 mCi is generally given following

thyroidectomy to ablate any residual tissue.

In the past, any patient receiving more than 30 mCi had to be hospitalized. That has changed with the NRC and is no longer required.

Thyroid Storm Sudden release of thyroid hormone

after radiation Concern for severely hyperthyroid

patients with severe symptoms. Can be avoided with pretreatment

using antithyroid drugs

Not normally a concern

Radioiodine Therapy Female patient’s must have pregnancy

test and must cease breastfeeding.

Following Therapy: No evidence of increased incidence of

cancer (including leukemia) No change in fertility rates or genetic

damage in children has been found.

Following Radioiodine treatment

Patient may experience:– Sore throat– Dysphagia– Increase in hyperthyroid symptoms

Patient should stay well hydrated and void frequently

18F – FDG imaging Shown to identify thyroid cancer even

when the I 131 imaging is negative. Gives improved anatomic localization

Parathyroid Usually 4 parathyroid glands. Location can vary:

– Alongside the thyroid– Within the thyroid gland– In the neck– In the mediastinum– Within the thymus– Among great vessels

Parathyroid function Synthesize, store and secrete parathyroid

hormone Regulates Calcium and phosphorus

metabolism in bone, kidneys and G.I. Tract Excessive secretion of parathyroid hormone

is hyperparathyroidism– Increased urinary secretion of calcium– Kidney stones– Bone mineral loss

Usually due to a parathyroid adenoma

Parathyroid Imaging Helps to localize the parathyroid adenoma

– Meaning less time in surgery 99mTc MIBI is most commonly used. Images are usually done at 30 minutes and again

at 90 to 150 minutes. Parathyroid adenomas are metabolically active

and are mitochondrial dense – where the MIBI will localize.

SPECT is helpful Image fusion with CT is gaining popularity. Allows

precise anatomical localization.

Parathyroid Imaging No patient prep

Large field of view should include salivary glands to mediastinum.

Parathyroid adenoma Mediastinum

Salivary Gland Warthin’s tumor

– Benign parotid gland lesions– More frequent in elderly men– Usually bilateral

5 – 15 mCi 99mTc pertechnetate Image 1 minute images for 20 mintues.