Thyroid Gland PDF

Thyroid gland/ Dr. Yousif Al-Jubori THYROID GLAND ANATOMY Thyroid gland is an endocrine gland present in front of the neck. It is composed of two lobes which are joined by isthmus resembling the butterfly. The gland moves on swallowing, since it is attached to the larynx by the pretracheal fascia....

Thyroid gland/ Dr. Yousif Al-Jubori THYROID GLAND ANATOMY Thyroid gland is an endocrine gland present in front of the neck. It is composed of two lobes which are joined by isthmus resembling the butterfly. The gland moves on swallowing, since it is attached to the larynx by the pretracheal fascia. Thyroid gland has two secretory cells: 1. Follicular cells secrete thyroid hormones: Tri-iodo-thyronine (T3), and Thyroxine (T4). 2. Parafollicular cells (C -cells) secrete calcitonin to reduce the serum calcium level. PHYSIOLOGY Tri-iodo-thyronine (T3) and thyroxine (T4) are stored in the gland as a colloid, and to be secreted from there to control metabolism according to body needs. Secretion of the hormones is under the influence of thyroid stimulating hormone (TSH) in the blood, which is released from the anterior pituitary gland according to negative feedback mechanism; (increased levels of thyroid hormones will suppress the secretion of TSH and vice versa). T3 is the active hormone and is fast acting (few hours). T4 is a slow acting hormone and takes about 7 days to act. These hormones affect many parts in the body, as; nervous system, cardiovascular system, gastrointestinal system, and reproductive system. GOITRE Goitre is defined as enlargement of the thyroid gland. It is detected clinically as thyroid mass in front of the neck which moves on swallowing. It may have retrosternal extension. It is commoner in females than males. Classification of goitre according to shape: 1. Diffuse goitre. 2. Nodular goitre (Multinodular goitre, or solitary thyroid nodule). Classification of goitre according to function: 1. Physiological goitre: It occurs due to increased physiological demands to thyroid hormones mostly in puberty, and pregnancy. 2. Colloid goitre (iodine deficiency goitre): Low thyroid hormones. 3. Hyperthyroid goitre: Increased levels of thyroid hormones, and low TSH. 4. Hypothyroid goitre: Decreased levels of thyroid hormones, and high TSH. 5. Neoplastic goitre: Benign thyroid tumour and malignant thyroid tumour. 1  Thyroid gland/ Dr. Yousif Al-Jubori Prevention of goitre: 1. Use iodised salt, milk, dairy products, eggs, and sea food including fish. 2. Avoid goitrogens; cabbage, and drugs (sulphonamide). 3. Thyroxine (Eltroxine) tab. 0.1 mg/ day in puberty goitre. HYPERTHYROID GOITRE (HYPERTHYROIDISM, THYROTOXICOSIS) Clinical features: 1. General: Weight loss in spite of good appetite, and hypolipidaemia. 2. CNS: Anxiety, irritability, agitation, tremor, heat intolerance and sweating. 3. CVS: Cardiac arrhythmias (tachycardia, atrial fibrillation, and extrasystoles). 4. Eye signs: Lid retraction, and exophthalmos. 5. GIT: Diarrhoea. Treatment: 1. Drugs: a. Antithyroid drug: Carbimazole 10 mg t.i.d. is used to reduce T3 and T4 levels in blood. b. B-blocker drug: Propranolol 20-40 mg t.i.d. is used to treat tachycardia. 2. Surgery: Subtotal thyroidectomy to reduce the functioning thyroid tissue. 3. Radioactive iodine: It is used as alternative to surgery to reduce the thyroid functioning tissue, but it is contraindicated in pregnancy. HYPOTHYROID GOITRE (HYPOTHYROIDISM, MYXOEDEMA) Clinical features: 1. General: Weight gain, slow hoars voice, and hyperlipidaemia. 2. CNS: Depression, tiredness, and cold intolerance. 3. CVS: Bradycardia, and hypotension. 4. Skin: Dry skin, alopecia and hair loss in the lateral third of eyebrows. 5. GIT: Constipation. 6. Developmental: Growth and mental retardation, and delayed puberty. Treatment: Thyroxine (Eltroxine) tab. 0.1- 0.2 mg/ day. THYROIDECTOMY Preoperative preparation for thyroidectomy: 1. Clinical examination of goitre (thyroid mass which moves on swallowing). 2  Thyroid gland/ Dr. Yousif Al-Jubori 2. Examination of the cervical lymph nodes. 3. Ultrasonography of thyroid gland: Assessment of the shape of thyroid gland; (diffuse goitre, multinodular goitre, and solitary thyroid nodule). 4. Thyroid function test (T3, T4, and TSH): Assessment of the function of thyroid gland; (euthyroid, hyperthyroid, or hypothyroid). 5. Indirect laryngoscopy: Assessment of vocal cord mobility before surgery. 6. Blood analysis: Complete blood picture, renal function test, fasting blood sugar, and blood group and crossmatching. 7. Chest X- ray, and X-ray of the neck (AP and lateral) to rule out retrosternal goitre, and feasibility of endotracheal intubation. 8. ECG, and echocardiography (on need). 9. Fine needle aspiration cytology (FNAC) in suspected malignancy. Indications of thyroidectomy: 1. Failure of medical treatment. 2. Nodular goitre. 3. Neoplastic goitre. 4. Pressure symptoms; (dyspnoea, or dysphagia). 5. Cosmesis (large size). Types of thyroidectomy: 1. Lobectomy which is combined with isthmectomy. 2. Subtotal thyroidectomy. 3. Nearly total or total thyroidectomy. Complications of thyroidectomy: 1. Bleeding due to slipped ligature. 2. Respiratory obstruction due to tension haematoma causes compression on the larynx. 3. Laryngeal nerve paralysis. a. Unilateral recurrent laryngeal nerve paralysis; hoarseness of voice. b. Bilateral recurrent laryngeal nerve paralysis; complete loss of voice and airway obstruction. The patient develops dyspnoea and need emergency tracheostomy. 4. Hypothyroidism occurs due to removal of excessive thyroid tissue during surgery. 5. Hypoparathyroidism occurs due to incidental removal of parathyroid glands during surgery and is treated by calcium and vitamin D3. 3  Thyroid gland/ Dr. Yousif Al-Jubori 6. Thyrotoxic crisis (thyroid storm): This is a surgical emergency occurs in thyrotoxic patient who is improperly prepared for surgery. The patient develops anxiety, agitation, hyperpyrexia, sweating, dehydration, diarrhoea, cardiac arrhythmias, and hypertension. Mortality is high in spite of treatment. Treatment: Treatment is supportive, and the patient should be managed in the RCU. a. O2 therapy and I.V. fluids to compensate fluid loss. b. Antithyroid drug: Carbimazole. c. B-blocker drug (propranolol) to control cardiac arrhythmia. d. Hydrocortisone I.V. as anti-inflammatory. e. Diazepam (valium) as anxiolytic. f. Antipyretics (paracetamol), and cold sponge to decrease hyperpyrexia. 4