Thyroid pathophysiology scintigraphy[1]

Thyroid

1. THYROID PATHOPHYSIOLOGY SCINTIGRAPHY NMT631

2. 2 THYROID PATHOPHYSIOLOGY Goiter Hyperthyroidism a . Graves’ Disease b. Toxic adenoma c . Toxic multinodular goiter Hypothyroidism Thyroiditis Thyroid carcinoma

3. 3 I. Goiter: enlarged thyroid gland May be present in hypo-, hyper-, and euthyroid states

4. I. Goiter: Physiological goiter: enlargement due to increased demand of thyroid hormones ( eg : puberty, pregnancy, etc ) Simple goiter: results from dietary iodine deficiency ( Low iodine → Low T 3 /T 4 levels → ↑ TSH → chronic thyroid excitation & hyperplasia . Excessive goiterogens : eg : cabbage, turnip & some drugs can suppress T 3 /T 4 levels and lead to goiter formation 4

5. 5 II. Hyperthyroidism (thyrotoxicosis) - All metabolic activities accelerated Symptoms: loss of weight tiredness, fine tremors, heat intolerance, wet/warm skin, easily excitable, difficulty sleeping, menstrual disturbances, diarrhea and anxiety; May or may not have goiter or exopthalmia.

6. II. Hyperthyroidism (thyrotoxicosis) - Different types a. Graves’ Disease (diffuse toxic goiter) b. Toxic adenoma (autonomous functioning nodule) c. Toxic multinodular goiter - Treatment options Suppressive thyroid medication Surgery Radioiodine therapy 6 Patient with hyperthyroidism. A wide-eyed, staring gaze, caused by overactivity of the sympathetic nervous system, is one of the classic features of this disorder. In Graves disease, one of the most important causes of hyperthyroidism, accumulation of loose connective tissue behind the orbits also adds to the protuberant appearance of the eyes.

7. 7 autoimmune disease accounts for 85% of cases of hyperthyroidism Symptoms: goiter, exophthalmos + other hyperthyroid symptoms Abnormal antibodies that mimic TSH stimulates excess thyroid hormone production and cause negative feedback for TSH production. II. Hyperthyroidism- a. Graves’ Disease Results in High T 3 /T 4 and low TSH levels in blood

8. 8 autonomously functioning thyroid nodule increased serum levels of T3 and/or T4 and suppression of serum TSH. Patient is not exopthalmous II. Hyperthyroidism- b. Toxic adenoma

9. 9 Multiple autonomously functioning overactive nodules producing excess thyroid hormones (increased serum levels of T3 and/or T4 and suppression of serum TSH) 2 nd most common cause of hyperthyroidism commonly found in areas of iodine deficiency and arises from a long-standing simple goiter Patient not exopthalmous and often seen in the elderly II. Hyperthyroidism- c. Toxic multinodular goiter

10. 10 III. Hypothyroidism - Primary: thyroid gland failure or congenital absence - Secondary: pituitary/hypothalmic failure The rate of metabolism slows causing mental and physical sluggishness.

11. 11 IV. Thyroiditis Multiple causes: - automimmune (Hashimoto’s disease) viral or bacterial Patient may exhibit symptoms of hyper- or hypothyroidism depending on stage of disease

12. IV. Thyroiditis Hashimoto's disease (chronic thyroiditis) Most common of thyroiditis caused by a reaction of the immune system against the thyroid gland (autoimmune disorder) causes hypothyroidism most often seen in middle-aged women 12

13. V. Thyroid carcinoma Four types: ► Papillary ► Follicular ► Medullary ► Anaplastic 13

14. V. Thyroid carcinoma Papillary about ½ of thyroid cancers slow growth excellent prognosis if detected early 14

15. V. Thyroid carcinoma Follicular about ¼ of thyroid cancers aggressive than papillary Prognosis directly related to tumor size [less than 1.0 cm good prognosis] 15

16. V. Thyroid carcinoma Medullary arises from parafollicular C cells good prognosis if restricted to thyroid gland poor prognosis if metastasized 16

17. V. Thyroid carcinoma Anaplastic least common type Undifferentiated poor prognosis poor response to therapy 17

18. V. Thyroid carcinoma Treatment ۞ Treatment for papillary and follicular thyroid carcinomas consists of thyroidectomy followed by radioiodine ablation. ۞ Treatment of medullary carcinoma consists of surgery and for anaplastic carcinoma the treatment is only palliative. 18

19. V. Thyroid carcinoma Statistics 19

20. 20 Ectopic tissue Thyroid Nodules “ Hot” nodules “Cold” nodules Multinodular gland Diffuse toxic goiter Thyroiditis Thyroid Carcinoma The Abnormal Scan

21. 21 Ectopic thyroid tissue The Abnormal Scan May occur in Neck (lingual thyroid), pelvis or retrosternally in medastinum A thyroid image showing no functioning thyroid tissue in the neck, but an area of avid tracer accumulation lying in the midline which corresponds to the posterior part of the tongue (lingual thyroid) An Atlas of Clinical Nuclear Medicine  - Ignac Fogelman, Michael Maisey, Susan E. M. Clarke marker

22. 22 Thyroid Nodules – Hot Nodule Increased radionuclide concentration > 99% benign May function independent of thyroid-pituitary axis feedback mechanism (autonomous nodules) The Abnormal Scan An Atlas of Clinical Nuclear Medicine  - Ignac Fogelman, Michael Maisey, Susan E. M. Clarke A solitary “toxic” nodule with suppression of the reminder of the thyroid

23. 23 Thyroid Nodules – Cold Nodule Non-functioning thyroid nodule Large majority benign but a small percentage (15-25%) cancerous The Abnormal Scan Pathological diagnosis confirmed a benign adenoma in the region of cold spot (arrows) Cardiothoracic Surgery Network An Atlas of Clinical Nuclear Medicine  - Ignac Fogelman, Michael Maisey, Susan E. M. Clarke

24. 24 Thyroid Nodules – Multinodular Goiter (MNG) Typically presents as an enlarged thyroid with multiple hot and/or cold nodules. The Abnormal Scan University Hospitals of Cleveland Multiple cold nodules Multiple hot nodules

25. 25 Diffuse Toxic Goiter (Graves’ disease) Characteristic findings : Thyromegaly Increased activity throughout the gland Frequently w/ pyrimidal lobe Increased perfusion and rapid uptake of tracer The Abnormal Scan Pyramidal lobe BrighamRAD Teaching Case The intensity of thyroid gland uptake exceeds the uptake in both salivary glands (arrows), background activity is markedly decreased, and the pyramidal lobe is clearly visible. All of these findings indicate a hyperfunctioning gland. There is no focal photopenic or focal hot area to suggest a nodule.

26. 26 Chronic Thyroiditis (Hashimoto’s thyroiditis) most common form of inflammatory disease of the thyroid Scan appearance varies from ‘uniform increased activity’ to ‘markedly depressed’ (sub-acute thyroiditis) radioiodine uptake. Positive thyroid antibodies The Abnormal Scan Sub-acute thyroiditis MIR teaching file

27. 27 Thyroid Carcinoma Usually demonstrated as cold nodules Whole body evaluations for metastasis done within 1-2 months of total or partial thyroidectomy The Abnormal Scan Abnormal diffuse activity in lungs, right neck, mediastinum, mid-abdomen, pelvis, left thigh, right thigh indicating metastasis MIR teaching file

28. 28 Remind the patient not to swallow during imaging Contamination I-131 and I-123 sodium iodide are excreted in the urine, saliva, and perspiration; 99mTc-Pertechnetate is excreted through urine. Protect self and equipment Take precautions to prevent contamination artifacts on images Artifacts & Pitfalls