Thyroid Gland PDF

THYROID GLAND By Dr.Salah Aljanaby Ass. Prof General and Laparoscopic Surgeon SURGICAL ANATOMY The normal thyroid gland weighs 20–25 g. The arterial supply is rich, and extensive anastomoses occur between the main thyroid arteries and branches of the...

THYROID GLAND By Dr.Salah Aljanaby Ass. Prof General and Laparoscopic Surgeon SURGICAL ANATOMY The normal thyroid gland weighs 20–25 g. The arterial supply is rich, and extensive anastomoses occur between the main thyroid arteries and branches of the tracheal and esophageal arteries There is an extensive lymphatic network within the gland. Although some lymph channels pass directly to the deep cervical nodes, the subcapsular plexus drains principally to the central compartment juxtathyroid – ‘Delphian’– and paratracheal nodes and nodes on the superior and inferior thyroid veins (level VI), and from there to the deep cervical (levels II, III, IV and V) and mediastinal groups of nodes (level VII) The normal parathyroid gland weighs up to 50 mg orange/brown colour Most adults have four parathyroid glands  PHYSIOLOGY Thyroxine The hormones tri-iodothyronine (T3) and l-thyroxine (T4) are bound to thyroglobulin within the colloid. Synthesis within the thyroglobulin complexis controlled by several enzymes, in distinct steps: trapping of inorganic iodide from the blood; oxidation of iodide to iodine; binding of iodine with tyrosine to form iodotyrosines; coupling of monoiodotyrosines and di-iodotyrosines to form T3 and T4. When hormones are required, the complex is resorbed into the cell and thyroglobulin is broken down. T3 and T4 are liberated and enter the blood, where they are bound to serum proteins: albumin, thyroxine-binding globulin (TBG) and thyroxinebinding prealbumin (TBPA). The small amount of hormone that remains free in the serum is biologically active. The metabolic effects of the thyroid hormones are due to unbound free T4 and T3 (0.03 and 0.3 per cent of the total circulating hormones, respectively). T3 is the more important physiological hormone and is also produced in the periphery by conversion from T4. T3 is quick acting (within a few hours), whereas T4 acts more slowly (4–14 days).  Parathormone The parathyroid glands secrete the 84-amino acid peptide parathyroid hormone (PTH), which controls the level of serum calcium in extracellular fluid PTH is released in response to a low serum calcium or high serum magnesium level. PTH activates osteoclasts to resorb bone, and increases calcium reabsorption from urine and renal activation of vitamin D with subsequent increased gut absorption of calcium. Renal excretion of phosphate is also increased.  Calcitonin The parafollicular C cells of the thyroid are of neuroendocrine origin and arrive in the thyroid via the ultimobranchial body They produce calcitonin which is a serum marker for recurrence of medullary thyroid cancer.  The pituitary–thyroid axis Synthesis and liberation of thyroid hormones from the thyroid is controlled by thyroid-stimulating hormone (TSH) from the anterior pituitary. Secretion of TSH depends upon the level of circulating thyroid hormones and is modified in a classic negative feedback manner. In hyperthyroidism, when hormone levels in the blood are high, TSH production is suppressed whereas in hypothyroidism it is stimulated. Regulation of TSH secretion also results from the action of thyrotrophin-releasing hormone (TRH) produced in the hypothalamus.  Thyroid-stimulating antibodies A family of IgG immunoglobulins bind with TSH receptor sites (TRAbs) and activate TSH receptors on the follicular cell membrane. They have a more protracted action than TSH (16–24 versus 1.5–3 hours) and are responsible for virtually all cases of thyrotoxicosis not due to autonomous toxic nodules. Serum concentrations are very low but their measurement is not essential to make the diagnosis  THYROID ENLARGEMENT The normal thyroid gland is impalpable. Goitre is generalised enlargement of the thyroid gland Isolated (solitary )swelling is discrete swelling (nodule) in one lobe with no palpable abnormality elsewhere Dominant swelling is discrete swellings with evidence of abnormality elsewhere in the gland CLASSIFICATION OF THYROID SWELLINGS  Simple goitre Aetiology stimulation of the thyroid gland by TSH, inappropriate secretion from a microadenoma in the anterior pituitary (which is rare), chronically low level of circulating thyroid hormones. The most important factor in endemic goitre is dietary deficiency of iodine defective hormone synthesis probably accounts for many sporadic goitres  The natural history of simple goitre Stages in goitre formation are: 1) Persistent growth stimulation causes diffuse hyperplasia; all lobules are composed of active follicles and iodine uptake is uniform. This is a diffuse hyperplastic goitre, which may persist for a long time but is reversible if stimulation ceases. 2) Later, as a result of fluctuating stimulation, a mixed pattern develops with areas of active lobules and areas of inactive lobules. 3) Active lobules become more vascular and hyperplastic until haemorrhage occurs, causing central necrosis and leaving only a surrounding rind of active follicles. 4) Necrotic lobules coalesce to form nodules filled either with iodine-free colloid or a mass of new but inactive follicles. 5) Continual repetition of this process results in a nodular goitre. Most nodules are inactive, and active follicles are present only in the internodular tissue.  Diagnosis The patient is euthyroid, The nodules are palpable and often visible; they are smooth, usually firm and not hard Goitre is painless and moves freely on swallowing. Hardness and irregularity, due to calcification, may simulate carcinoma. A painful nodule, sudden appearance or rapid enlargement of a nodule raises suspicion of carcinoma but is usually due to haemorrhage into a simple nodule. Differential diagnosis from autoimmune thyroiditis may be difficult and the two conditions frequently coexist.  Investigations 1) Thyroid function should be assessed to exclude mild hyperthyroidism, 2) Thyroid antibodies tested to differentiate from autoimmune thyroiditis. 3) Ultrasound is the gold standard assessment 4) FNAC is only required for a nodule within the goitre that demonstrates ultrasonic features of concern. The biopsy should be performed under ultrasonic guidance to ensure the correct nodule is sampled. 5) CT scan of the thoracic inlet is the best modality to assess tracheal or oesophageal compression.  Complications o Tracheal obstruction may be due to gross lateral displacement or compression in a lateral or anteroposterior plane by retrosternal extension of the goitre o SECONDARY THYROTOXICOSIS Transient episodes of mild hyperthyroidism are common, occurring in up to 30% of patients. o CARCINOMA An increased incidence of cancer (usually follicular) has been reported from endemic areas.  Prevention and treatment of simple goitre In endemic areas the incidence of goitre has been strikingly reduced by the introduction of iodised salt. In the early stages, a hyperplastic goitre may regress if thyroxine is given in a dose of 0.15–0.2 mg daily for a few months. Although the nodular stage of simple goitre is irreversible, more than half of benign nodules will regress in size over 10 years. Most patients with multinodular goitre are asymptomatic and do not require operation. Surgery is indicated for nodular goitres 1. features of underlying malignancy 2. swallowing symptoms i 3. cosmetic reasons i 4. tracheal compression  There is a choice of surgical treatment in multinodular goitre : Total thyroidectomy with immediate and lifelong replacement of thyroxine. Subtotal thyroidectomy partial resection of each lobe removing the bulk of the gland, leaving up to 8 g of relatively normal tissue in each remnant. COLLOID GOITRE MULTINODULAR GOITRE  Clinically discrete swellings common palpable in 3–4% of the adult population three to four times more frequent in women than men.  Diagnosis. About 70% of discrete thyroid swellings are clinically isolated and about 30% are dominant. The importance of discrete swellings lies in the risk of neoplasia compared with other thyroid swellings. 15% of isolated swellings prove to be malignant and an additional 30–40% are follicular adenomas. The remainder are non-neoplastic, largely consisting of areas of colloid degeneration, thyroiditis or cysts.  Investigation THYROID FUNCTION If hyperthyroidism ‘toxic adenoma’ or toxic multinodular goitre. The combination of toxicity and nodularity is indication for isotope scanning to localise the area(s) of hyperfunction. AUTOANTIBODY TITRES chronic lymphocytic thyroiditis. ISOTOPE SCAN except when toxicity is associated with nodularity. ULTRASONOGRAPHY ultrasonic features in a thyroid swelling associated with thyroid neoplasia, including microcalcification and increased vascularity, but only macroscopic capsular breach and nodal involvement are diagnostic of malignancy. FINE-NEEDLE ASPIRATION CYTOLOGY FNAC should be used, ideally under ultrasound guidance,. FNAC is reliable in identifying papillary thyroid cancer but cannot distinguish between a benign follicular adenoma and follicular carcinoma, as this distinction is dependent not on cytology but on histological criteria, which include capsular and vascular invasion. FNAC is both highly specific and sensitive.  RADIOLOGY Plain films have previously been used to assess tracheal compression and deviation CT scanning is also useful if ultrasound has identified metastatic disease in the neck as it can assist surgical planning and also assess the superior mediastinum and lungs LARYNGOSCOPY Flexible laryngoscopy has rendered indirect laryngoscopy obsolete and is widely used preoperatively to determine the mobility of the vocal cords. The presence of a unilateral cord palsy coexisting with an ipsilateral thyroid nodule of concern is usually diagnostic of malignant disease.  CORE BIOPSY rarely indicated in thyroid masses useful in the rapid diagnosis of widely invasive malignant disease, for example anaplastic carcinoma, or in the diagnosis of lymphadenopathy.  The main indication for operation is the risk of neoplasia, which includes follicular adenoma as well as malignant swellings. 50% of isolated swellings and 25% of dominant swellings should be removed on the grounds of neoplasia. the age and sex of the patient and the size of the swelling may be relative indications for surgery clinical criteria to assist in selection for operation according to the risk of neoplasia and malignancy…. hard, irregular swelling …..RLN paralysis……Deep cervical ymphadenopathy The incidence of thyroid carcinoma in women is about three times that in men, but a discrete swelling in a male is much more likely to be malignant than in a female The risk of carcinoma is increased at either end of the age range and a discrete swelling in a teenager of either sex must be provisionally diagnosed as carcinoma. The risk increases as age advances beyond 50 years, more so in males. INDICATIONS FOR OPERATION IN THYROID SWELLINGS.  Selection of thyroid procedure The choice of thyroid operation depends on: diagnosis (if known preoperatively); risk of thyroid failure; risk of RLN injury; risk of recurrence; Graves’ disease; multinodular goitre; differentiated thyroid cancer; risk of hypoparathyroidism.  Retrosternal goitre Arise from the slow growth of a multinodular gland down in to the mediastinum. As the gland enlarges within the thoracic inlet, pressure may lead to dysphagia, tracheal compression and eventually airway symptoms. Patient should be considered for surgery if there is significant airway compression  HYPERTHYROIDISM Thyrotoxicosis symptoms due to a raised level of circulating thyroid hormones, is not responsible for all manifestations of the disease. Clinical types are: diffuse toxic goitre (Graves’ disease); toxic nodular goitre; toxic nodule; hyperthyroidism due to rarer causes.  Clinical features The symptoms are: tiredness emotional lability heat intolerance weight loss excessive appetite palpitations. The signs of thyrotoxicosis are : tachycardia hot, moist palms exophthalmos eyelid lag/retraction agitation thyroid goitre and bruit.  Diffuse toxic goitre diffuse vascular goitre appearing at the same time as hyperthyroidism, usually occurs in younger women frequently associated with eye signs. The syndrome is that of primary thyrotoxicosis 50% of patients have a family history of autoimmune endocrine diseases.  Toxic nodular goitre A simple nodular goitre is present for a long time before the hyperthyroidism usually in the middle-aged or elderly very infrequently is associated with eye signs. The syndrome is that of secondary thyrotoxicosis.  Toxic nodule solitary overactive nodule, which may be part of a generalised nodularity or a true toxic adenoma. It is autonomous and its hypertrophy and hyperplasia are not due to TSH-RAb. TSH secretion is suppressed by the high level of circulating thyroid hormones and the normal thyroid tissue surrounding the nodule is itself suppressed and inactive. GRAVES’ DISEASE.  Principles of treatment of thyrotoxicosis Non-specific measures are rest and sedation specific measures, i.e. the use of antithyroid drugs, surgery and radioiodine.  ANTITHYROID DRUGS Those in common use are carbimazole and propylthiouracil. used to restore the patient to a euthyroid state and to maintain this for a prolonged period in the hope that a permanent remission will occur, i.e. that production of thyroid-stimulating antibodies (TSH-RAb) will diminish or cease. Antithyroid drugs cannot cure a toxic nodule. Advantages. No surgery no use of radioactive materials. Disadvantages. Treatment is prolonged failure rate is at least 50%. The duration of treatment may be tailored to the severity of the toxicity, with milder cases being treated for only 6 months and severe cases for 2 years before stopping therapy.  SURGERY In diffuse toxic goitre and toxic nodular goitre with overactive internodular tissue, surgery cures by reducing the mass of overactive tissue by reducing the thyroid below a critical mass. Advantages. The goitre is removed the cure is rapid and the cure rate is high if surgery has been adequate. Disadvantages. Recurrence of thyrotoxicosis occurs in at least 5% of cases when subtotal thyroidectomy is carried out. There is a risk of permanent hypoparathyroidism and nerve injury. Young women tend to have a poorer cosmetic result from the scar. Every operation carries a risk, but with suitable preparation and an experienced surgeon the mortality is negligible and the morbidity low. COMPARISON OF SURGICAL OPTIONS FOR GRAVES’ DISEASE.  RADIOIODINE Radioiodine destroys thyroid cells and, as in thyroidectomy, reduces the mass of functioning thyroid tissue to below a critical level. Advantages. No surgery no prolonged drug therapy. Disadvantages. Isotope facilities must be available. The patient must be quarantined while radiation levels are high and avoid pregnancy and close physical contact, particularly with children. Eye signs may be aggravated.  Choice of therapy Each case must be considered individually. guiding principles on the most satisfactory treatment for a particular toxic goitre at a particular age be modified according to the facilities available and the personality and wishes of the individual patient, business or family commitments and any other coexistent medical or surgical condition. Access to post- treatment care and availability of replacement thyroxine can be important considerations in resource-poor countries. In advising treatment, compliance, influenced by social and intellectual factors, is important; many patients cannot be trusted to take drugs regularly if they feel well, and indefinite follow-up, which is essential after radioiodine or subtotal thyroidectomy is a burden for all.  DIFFUSE TOXIC GOITRE Most patients have an initial course of antithyroid drugs with radioiodine for relapse. Exceptions are those who refuse radiation, have large goitres, progressive eye signs or are pregnant. TOXIC NODULAR GOITRE Toxic nodular goitre is often large and uncomfortable and enlarges still further with antithyroid drugs. A large goitre should be treated surgically because it does not respond as well or as rapidly to radioiodine or antithyroid drugs as does a diffuse toxic goitre. TOXIC NODULE Surgery or radioiodine treatment is appropriate. Radioiodine is a good alternative for patients over the age of 45 years because the suppressed thyroid tissue does not take up iodine and thus there is minimal risk of delayed thyroid insufficiency. FAILURE OF PREVIOUS TREATMENT WITH ANTITHYROID DRUGS OR RADIOIODINE In this case, surgery or thyroid ablation with 123I is appropriate.  Surgery for thyrotoxicosis Preoperative preparation aims to make the patient biochemically euthyroid at operation. Preparation is as an out-patient and only rarely is admission to hospital necessary on account of severe symptoms at presentation, failure to control the hyperthyroidism or non- compliance with medication.  Carbimazole 30–40 mg per day is the drug of choice for preparation. When euthyroid (after 8–12 weeks), the dose may be reduced to 5 mg 8-hourly or a ‘block and replace’ regime used. In this case, the high dose of carbimazole is continued to inhibit T3 and T4 production and a maintenance dose of 0.1–0.15 mg of thyroxine is given daily. The last dose of carbimazole may be given on the evening before surgery. Iodides are not used alone because, if the patient needs preoperative treatment, a more effective drug should be given.  An alternative method of preparation is to abolish the clinical manifestations of the toxic state, using β-adrenergic blocking drugs. These act on the target organs and not on the gland itself. Propranolol also inhibits the peripheral conversion of T4 to T3. The appropriate dosages are propranolol 40 mg t.d.s. or the longer acting nadolol 160 mg once daily. Clinical response to β-blockade is rapid and the patient may be rendered clinically euthyroid and operation arranged in a few days rather than weeks. β-adrenergic blocking drugs do not interfere with synthesis of thyroid hormones, and hormone levels remain high during treatment and for some days after thyroidectomy. It is, therefore, important to continue treatment for 7 days postoperatively.  Iodine may be given with carbimazole or a β-adrenergic blocking drug for 10 days before operation. Iodide alone produces a transient remission and may reduce vascularity. POSTOPERATIVE COMPLICATIONS 1) Haemorrhage is the most frequent life-threatening complication of thyroidectomy Around 1 in 50 patients will develop a haematoma, and in almost all cases this will develop in the first 24 hours. If an arterial bleed occurs, the tension in the central compartment pressure can rise until it exceeds venous pressure. Venous oedema of the larynx can then develop and cause airway obstruction leading to death. If a haematoma develops, clinical staff should know to remove skin sutures in order to release some pressure and seek senior advice immediately. Endotracheal intubation should be used to secure the airway while the haematoma is evacuated and the bleeding point controlled.  2. Recurrent laryngeal nerve paralysis and voice change RLN injury may be unilateral or bilateral, transient or permanent. Injury to the external branch of the superior laryngeal nerve is more common because of its proximity to the superior thyroid artery. This leads to loss of tension in the vocal cord with diminished power and range in the voice. Patients, particularly those who use their voice professionally, must be advised that any thyroid operation will result in change to the voice even in the absence of nerve trauma. 3.Thyroid insufficiency Following total thyroidectomy, clearly thyroxine replacement will be required. Around one in three patients who has a lobectomy will require supplementation; rates are higher in those with thyroid autoantibodies. Subtotal thyroidectomy was at one time performed with the aim of leaving sufficient tissue to maintain thyroid function. 4.Parathyroid insufficiency This is due to removal of the parathyroid glands or infarction through damage to the parathyroid end arteries; The incidence of permanent hypoparathyroidism should be less than 1% and most cases present dramatically 2–5 days after operation but, very rarely, the onset is delayed for 2–3 weeks or a patient with marked hypocalcaemia may be asymptomatic. The complication is limited to total thyroidectomy, as when lobectomy is performed the contralateral parathyroid glands are sufficient to maintain calcium levels. 5,Thyrotoxic crisis (storm) . acute exacerbation of hyperthyroidism. . occurs if a thyrotoxic patient has been inadequately prepared for thyroidectomy and is now extremely rare.  Very rarely, a thyrotoxic patient presents in a crisis and this may follow an unrelated operation.  Symptomatic and supportive treatment is for dehydration, hyperpyrexia and restlessness. This requires the administration of intravenous fluids, cooling the patient with ice packs, administration of oxygen, diuretics for cardiac failure, digoxin for uncontrolled atrial fibrillation, sedation and intravenous hydrocortisone.  Specific treatment is by carbimazole 10–20 mg 6-hourly, Lugol’s iodine 10 drops 8-hourly by mouth or sodium iodide 1g i.v. Propranolol intravenously (1–2 mg) or orally (40 mg 6-hourly) will block β-adrenergic effects. 6.Wound infection Cellulitis requiring prescription of antibiotics A significant subcutaneous or deep cervical abscess is exceptionally rare and should be drained. 7.Hypertrophic or keloid scar This is more likely to form if the incision overlies the sternum and in dark skinned individuals. Intradermal injections of corticosteroid should be given at once and repeated monthly if necessary. Scar revision rarely results in significant long-term improvement. 8.Stitch granuloma This may occur with or without sinus formation and is seen after the use of non- absorbable, particularly silk, suture material. Absorbable ligatures and sutures should be used throughout thyroid surgery. Some surgeons use a subcuticular absorbable skin suture rather than the traditional skin clips or staples.  NEOPLASMS OF THE THYROID Classification of thyroid neoplasims  Benign tumours Follicular adenomas present as clinically solitary nodules distinction between a follicular carcinoma and an adenoma can only be made by histological examination; in the adenoma there is no invasion of the capsule or of pericapsular blood vessels. For this reason, FNA, which provides cytologic detail but not tissue architecture, cannot differentiate between benign and malignant follicular lesions. Diagnosis and treatment is therefore, by wide excision, i.e. total lobectomy. The remaining thyroid tissue is normal so that prolonged follow-up is unnecessary.  Malignant tumours  The vast majority of primary malignancies are carcinomas derived from the follicular cells  Such tumors were thought of as differentiated (papillary, follicular and Hürthle cell) and undifferentiated (anaplastic).  The parafollicular C cells can undergo malignant transformation into medullary carcinoma, and thyroid lymphoma is another primary thyroid malignancy.  the thyroid can be involved by direct spread from surrounding structures (larynx and oesophagus) or metastases (most commonly from renal cell carcinoma).  Lymph node and blood-borne metastases of thyroid cancer occur primarily to bone and lung and may be the mode of presentation  Aetiology of malignant thyroid tumours The great majority of thyroid cancers have no known aetiological factor. The most important identifiable aetiological factor in differentiated thyroid carcinoma (particularly papillary) is irradiation of the thyroid under 5 years of age. Short latency aggressive papillary cancer is associated with the ret/PTC3 oncogene and later developing, possibly less aggressive, cancers with ret/PTC1. The incidence of follicular carcinoma is high in endemic goitrous areas, possibly due to TSH stimulation. Malignant lymphomas sometimes develop in autoimmune thyroiditis  Clinical features of thyroid cancers The annual incidence is about 0.6 per million of the population The sex ratio is three females to one male. The mortality rates remain static at over 80% 5-year survival for all groups. anaplastic carcinoma predicts poor outcome differentiated carcinomas generally having excellent outcomes. The most common presenting symptom is a thyroid swelling Enlarged cervical lymph nodes may be the presentation of papillary carcinoma (PTC). RLN paralysis is very suggestive of locally advanced disease. Anaplastic growths are usually hard, irregular and infiltrating. A differentiated carcinoma may be suspiciously firm and irregular, but is often indistinguishable from a benign swelling. Small papillary tumours may be impalpable, even when lymphatic metastases are present. Pain, often referred to the ear, is suggestive of nerve involvement from infiltrating tumours.  Diagnosis of thyroid neoplasms Clinical history and examination continue to be the cornerstone of diagnosis of thyroid neoplasms. radiation exposure and family history Examination of the central neck and regional lymphatics should be combined with assessment of vocal cord function. Biochemical assessment of thyroid function Following initial assessment, the next step is ultrasound. This non-invasive investigation is most accurate at assessing thyroid swellings. Not only can a judgement be made on the presence, size and number of thyroid nodules present, but an estimate of risk of malignancy can be made depending on these findings. Following ultrasound, lesions can be categorised as benign, indeterminate or malignant. Benign lesions require no further assessment unless surgery is considered for compressive symptoms. Indeterminate or malignant lesions should be investigated with FNAC.  Occasionally, the surgeon will encounter a thyrotoxic patient. Such cases are one of the few indications for a radioiodine uptake scan. This allows assessment of the function of a nodule. Hot nodules are very rarely malignant. Cold nodules will require assessment as for all other thyroid neoplasms. Following clinical, ultrasound and cytological assessment, the vast majority of lesions will be characterised as benign, malignant or indeterminate. Further treatment will be planned accordingly.  Papillary carcinoma is the most common thyroid malignancy. its propensity for lymph node metastases. more common in younger patients Distant metastases are uncommon in PTC. ‘papillary microcarcinoma’. This term is used to describe PTC that is