THYROID PATHOPHYSIOLOGY SCINTIGRAPHY

NMT631

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THYROID PATHOPHYSIOLOGY

I. GoiterII. Hyperthyroidism

a. Graves’ Disease b. Toxic adenoma c. Toxic multinodular goiter

III. HypothyroidismIV. ThyroiditisV. Thyroid carcinoma

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I. Goiter:

• enlarged thyroid gland

– May be present in hypo-, hyper-, and euthyroid states

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 T3/T4 levels → ↑ TSH → chronic thyroid excitation & hyperplasia.

– Excessive goiterogens: eg: cabbage, turnip & some drugs can suppress T3/T4 levels and lead to goiter formation

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II. Hyperthyroidism (thyrotoxicosis)

- All metabolic activities acceleratedSymptoms:

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.

II. Hyperthyroidism (thyrotoxicosis)

- Different typesa. Graves’ Disease (diffuse toxic goiter) b. Toxic adenoma (autonomous functioning nodule) c. Toxic multinodular goiter

- Treatment optionsSuppressive thyroid medicationSurgeryRadioiodine therapy

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Patient with hyperthyroidism. A wide-eyed, staring gaze, caused by overactivity of the sympathetic nervous system, is one of theclassic 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.

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• 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 T3/T4 and low TSH levels in blood

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• 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

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Multiple autonomously functioning overactive nodules producing excess thyroid hormones (increased serum levels of T3 and/or T4 and suppression of serum TSH)

• 2nd 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

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III. Hypothyroidism

- Primary: thyroid gland failure or congenital absence

- Secondary: pituitary/hypothalmic failure

The rate of metabolism slows causing mental and physical sluggishness.

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IV. Thyroiditis

• Multiple causes: - automimmune (Hashimoto’s

disease) viral or bacterial

• Patient may exhibit symptoms of hyper- or hypothyroidism depending on stage of disease

IV. ThyroiditisHashimoto'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

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V. Thyroid carcinomaFour types:

►Papillary

► Follicular

► Medullary

► Anaplastic

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V. Thyroid carcinoma Papillary

• about ½ of thyroid cancers• slow growth• excellent prognosis if detected early

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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]

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V. Thyroid carcinoma Medullary

• arises from parafollicular C cells

• good prognosis if restricted to thyroid gland

• poor prognosis if metastasized

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V. Thyroid carcinoma Anaplastic

• least common type

• Undifferentiated

• poor prognosis

• poor response to therapy17

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.

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V. Thyroid carcinoma Statistics

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• Ectopic tissue • Thyroid Nodules

– “Hot” nodules– “Cold” nodules– Multinodular gland

• Diffuse toxic goiter• Thyroiditis• Thyroid Carcinoma

The Abnormal Scan

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Ectopic thyroid tissueThe 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

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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

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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

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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

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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.

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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 thyroiditisMIR teaching file

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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

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• 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