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EMBRYOLOGY Greek (shield-shaped) Develops as a thickening in the pharyngeal floor at the base of the tongue at the foramen cecum that elongates inferiorly as the thyroglossal duct, dividing into two lobes as it descends through the neck. medial anlage(endoderm) give rise to the thyroid follicular cells –fuse with- lateral anlage (neuroectoderm) which originate from 4th branchial pouch give rise to parafollicular (C) cells. ANATOMY Largest endocrine gland (20 grams) Brown and firm Two lobes , isthmus , pyramidal lobe (50%) Highly vascularized Location; anterior in the neck extends from middle of thyroid cartilage to just above clavicle C5-T1 2nd-4th tracheal ring(isthmus) Coverings; skin, platysma, strap muscle (sternothyroid, sternohyoid, superior belly of omohyoid), deep cervical fascia(pretracheal fascia), true inner capsule(lobules). ARTERIAL SUPPLY -The superior thyroid artery is the first branch of the external carotid artery . -The inferior thyroid artery branch of the thyrocervical trunk, which comes off the subclavian artery. -Thyroidea ima arises from aorta (from innominate 1-4 %) VENOUS DRAINAGE - The superior and middle thyroid veins drain into the internal jugular veins. - The inferior thyroid vein drains into the brachiocephalic vein. LYMPHATIC DRAINAGE Quite extensive and flows multidirectionally. Immediate drainage flows first to the periglandular nodes, then to the prelaryngeal (Delphian), pretracheal, and paratracheal nodes along the recurrent laryngeal nerve, and then to mediastinal lymph nodes. INNERVATION - superior, middle, and inferior cervical sympathetic ganglia. - parasympathetic fibers from the vagus nerves. NERVES Recurrent laryngeal N: innervate all the intrinsic muscles of larynx except the cricothyroid Left: from vagus , crosses the aortic arch, loops around ligamentum arteriosum, ascends in the tracheoesophageal groove. Right: from vagus , crosses the RT subclavian artery (more oblique course). Non-recurrent LT: rare, in situs inversus. RT: 1%, associated with vascular anomaly Superior LN: (external branch) innervate cricothyroid muscle branch of vagus, travels with STA HISTOLOGY Follicle : structural unit of T. gland Lobule: 20-40 follicles. Adult thyroid: 3 million follicles PHYSIOLOGY IODINE daily requirement: 0.1 mg sources: milk, fish, eggs, salt converted to iodide (deoxidation) in stomach absorbed in jejunum stored in thyroid ( >90%) cleared by (thyroid 30%), (kidneys 70%) STIMULANTS - TSH - EPINEPHRINE - HUMAN CHORIONIC GONADOTROPHINS -pregnancy -gynecologic malignancies (hydatidiform mole) -AUTO REGULATION: -low iodine intake -iodine excess T4 T3 THYROID (100%) THYROID (20%) LIVER, MUSCLE KIDNEYS ANT. PITUITARY MORE LESS LESS MORE (4 TIMES) Active form MORE LESS 7 DAYS 1 DAY PRODUCTION PLASMA LEVEL POTENCY TIGHTNESS TO PLASMA PROTEIN HALF-LIFE THYROID HORMONES FUNCTION Fetal brain development. Skeletal maturation. Increase oxygen consumption, basal metabolic rate (Na+/K+ ATPase). Heat production. Positive inotropic and chronotropic effects on heart (Ca+ ATPase). Maintain normal hypoxic and hypercapnic drive in resp. center in the brain. Increase bone & protein turnover. Increase the speed of muscle contraction & relaxation. + Glycogenolysis, hepatic gluconeogenesis. + Intestinal glucose absorption. + Cholesterol synthesis & degradation. THYROID FUNCTION TEST TSH : most sensitive & specific test for DX hypo-hyperthyroidism & for optimizing T4 therapy. T4 (total) increase in – hyperthyroidism. - elevated Tg (pregnancy..). decrease in – hypothyroidism. - decreased Tg (nephrotic S.). T3 (total) : important in – T3 thyrotoxicosis . (clinical hyperthyroidism with normal T4) - increased in early hypothyroidism. T4 (free) -early hyperthyroidism ( normal total T4, high free T4). -Refetoff syndrome ; end organ resistance to T4 (high T4, normal TSH). T3 (free) -important in DX of early hyperthyroidism with normal total T4 &T3 . THYROID FUNCTION TEST THYROTROPIN-RELEASING HORMONE (TRH) To evaluate pituitary TSH secretory function THYROID ANTIBODIES To diagnose autoimmune thyroiditis (hashimoto , graves) SERUM THYROGLOBULIN ( Tg) Made only by thyroid tissues Important in DX of: -thyroiditis, graves, toxic MN goiter. -detect recurrence of diff. thyroid cancer (most important). SERUM CALCITONIN Sensitive marker of medullary T. cancer. THYROID IMAGING ULTRASOUND - Non invasive, no radiation - Solid vs cystic - Multicentricity - Assess lymphadenopathy - Guide FNAB THYROID IMAGING RADIONUCLIDE IMAGING I 123 : - low dose of radiation - half-life 12-14 hours - image lingual thyroid tissues I 131 : - higher dose of radiation - half-life 8-10 days - screen & treat metastasis of diff. thyroid cancer “ both demonstrate the size , shape & the functional activity ” Tc 99m : - short half-life & low dose of radiation - sensitive for LN metastasis FDG PET Scan ( F-fluorodeoxyglucose Positron emission Tomography) - screen for mets when other IXs are negative - screen for non palbable thyroid lesions THYROID CT SCAN THYROID MRI HYPERTHYROIDISM HYPOTHYROIDISM Heat intolerance Cold intolerance Wt loss (most common ) Wt gain Hyper-activity, nervousness, restlessness Hypo-activity, decreased mobility, Fatigue Fatigue Diarrhea Constipation Amenorrhea Menorrhagia Warm moist skin Dry cold thick skin Hair loss Brittle hair & nail Breathlessness, SOB, wheezing, stridor ------------- Hand tremor ------------- Staring gaze ------------- Insomnia Lethargy, psycho-motor retardation HYPERTHYROIDISM HYPOTHYROIDISM Tachycardia Bradycardia Edema Edema Normal or high body temperature Low body temperature ----------------- Coarsening of voice, Puffy and coarse face DIFFUSE TOXIC GOITER (GRAVES DISEASE) -most common cause of hyperthyroidism 70% -male : female ( 1:5) -age 40-60 years -autoimmune with familial predisposition -extra-thyroidal pathologies (eye, skin, …) -treatment : -anti-thyroid drugs -radio-active iodine therapy (I131) -surgical INDICATIONS OF SURGERY -confirmed or suspicious of malignancy -young patients -pregnant or desire to conceive -reaction to anti-thyroid drugs -compressive symptoms -contraindicated RAI therapy TYPES OF SURGERY -total or near total thyroidectomy for severe cases -subtotal thyroidectomy (leaving 4-7 gms) - bilateral subtotal -total on one side &subtotal on the other side Hartley dunhill operation TOXIC MN GOITER -end stage of non-toxic MNG -needs several years to occur -same like GRAVES with no extrathyroidal manifestations -treatment is subtotal thyroidectomy TOXIC ADENOMA (PLUMMERS DISEASE) -solitary hot nodule with rapid growth -size usually > 3cm -younger pts -rarely malignant -treatment : lobectomy + isthmusectomy THYROID STORM -Hyperthyroidism + fever + agitation or depression + cardio-vascular dysfunction -causes : infection trauma surgery drugs (amiodarone) Treatment : medical (ICU) THYROIDITIS Thyroid is resistant to infection - extensive blood and lymphatic supply - high iodine content - fibrous capsule • 1- Acute (suppurative) thyroiditis -streptococcus + anaerobes 70% -more common in children -symptoms -severe neck pain -fever, chills -odynophagia -dysphonia -DX : leukocytosis FNAB ; gram stain, culture, cytology -treatment : IV antibiotic + drainage of abscess 2- Subacute thyroiditis -painful, painless -unknown etiology..viral, autoimmune -stages -initial hyperthyroid phase -euthyroid phase -hypothyroid phase 25% -resolution phase > 90% -treatment - medical - thyroidectomy (rare) -no response to medical RX -recurrent 3-Chronic lymphocytic (hashimoto) thyroiditis -most common inflammatory thyroid disorder -leading cause of hypothyroidism -autoimmune, inherited -male : female ( 1:15) -age 30-50 year -presentation –mild, diffuse & firm thyroid enlargement -painless -hypothyroidism 20% -hyperthyroidism 5% -treatment -medical -thyroidectomy(rare) indicated if -suspicious for malignancy -compressive symptoms -cosmetic 4- Riedels thyroiditis -invasive fibrous thyroiditis -replacement of thyroid T by fibrous T -rare -autoimmune -more in females -age 30-60 year -presentation -hard ant. neck mass (fixed) -compressive symptoms -hypothyroidism -hypoparathyroidism -DX : open BX -treatment -medical -surgical -wedge resection of isthmus to decompress the trachea GOITER (ANY ENLARGMENT OF THYROID GLAND) DIFFUSE, UNINODULAR, MULTINODULAR TOXIC, NON-TOXIC CAUSES -ENDEMIC : low iodine intake -MEDICATIONS: iodide, amiodarone, lithium -THYROIDITIS : sub-acute, chronic -FAMILIAL : enzyme defect -NEOPLASM : adenoma, carcinoma -GOITROGENS : kelp, cassava, cabbage INDICATIONS OF SURGERY IN SIMPLE GOITER -obstructive symptoms -substernal extention -suspicious of malignancy -increase in size despite T4 suppresion -cosmetic “ subtotal thyroidectomy” SOLITARY THYROID NODULE FNAB 1*NON DIAGNOSTIC … repeat 2*MALIGNANT…thyroidectomy 3*SUSPICIOUS(FOLLICULAR) =RAI scan -cold… thyroidectomy -hot … RAI / thyroidectomy 4*BENIGHN -Cyst.. Aspirate.. Reaccumulates#3 thyroidectomy -Colloid nodule.. Observe.. Continued growth or compressive symptom thyroidectomy THYROID CYST -Resolve with aspiration 75% -indication of thyroidectomy -failure to do complete aspiration - > 4cm -complex (solid-cystic).. 15% malig. -recurrence after 3 aspiration THYROID CANCER 1% of all cancers. Male : female ( 1: 4 ). The usual presentation is neck swelling. Well differentiated to anaplastic. Curable to very poor prognosis. Surgical treatment is controversial. PAPILLARY CARCINOMA 80%. Male : female (1 : 2). Mean age (30-40 years). > in children. > in individuals who exposed to external radiation. Presentation –euthyroid - neck mass ( painless ) -dysphagia, dyspnea, dysphonia ( localy invasive ) US to evaluate the contra lateral lobe & L-Nodes. Multifocality 85%. L-Nodes metastasis is common. Distant mets ( uncommon) at time of DX but with time might reach up to 20 % …. Lung is the most common site then bone, liver & brain. Prognosis: 10-year survival > 95% Histology ( 3 variants): -pure papillary -mixed ( papillary + follicular) -follicular variant of papillary “ All behave biologically as papillary ca “ -other rare variant (1%) with worse prognosis; tall cell,insular,columnar,clear cell,trabicular,diffuse sclerosing, poorly diff. Occult or minimal micro carcinoma -incidental or autopsy findings -< 1 cm -no thyroid capsule invasion -no angioinvasion -no LN or distant mets “ best prognosis “ Prognosis 1. AGES scoring system Low risk High risk Age Young < 40 Old >40 Histological grade Well diff. Poorly diff. Extra thyroidal invasion No Yes Tumor size (1ry lesion) Small size < 5cm Large > 5cm Distant metastasis No Yes Prognosis 2. 3. 4. 5. DeGroot scale class 1 : intrathyroidal class 2 : cervical LN mets class 3 : extrathyroidal invasion class 4 : distant metastasis MACIS scale AMES scale TNM TREATMENT SURGICAL TREATMENT OCCULT/MINIMAL PAPILLARY CA LOBECTOMY ALL OTHER PAPILLARY CA TOTAL OR NEAR TOTAL THYROIDECTOMY BOTH WITH CENTRAL LYMPHADENECTOMY Advantages of total thyroidectomy 1. 2. 3. 4. 5. 6. 7. Enables the use of RAI to detect and treat residual tissue & mets. Makes serum Tg more sensitive to detect recurrence. Eliminate contra lateral occult ca (85% of papillary ca are bilateral). Decreases the 1% risk of progression to undiff. Or anaplastic variants. Reduces the need for 2nd surgery. Complication rate < 2%. Improves survival. Advantages of hemithyroidectomy 1. 2. 3. 4. 5. Less complication rate than total. Recurrence in remaining lobe is unusual (<5%). Most of recurrences are curable by surgery. Total & hemithyroidectomy almost have the same prognosis. Multicentricity usually has little prognostic significance . FOLLICULAR CARCINOMA 10%. Male : female (1 : 3). Mean age (50years). More common in iodine deficient area so iodine supplementation decrease the incidence. Presentation –euthyroid, - hyperthyroidism (<1%) - solitary neck mass ( painless ) - sometimes rapid increase in size - pain due to hemorrhage (uncommon) L-Nodes metastasis is uncommon ( 5%). Distant mets > papillary ( venous spread). FNAB is unable to diff. benign from malignant. Goes with malignancy –older age -large tumors > 4cm -distant mets Usually solitary capsulated lesion. Capsular & vascular invasions are common. SURGICAL TREATMENT FNAB : if follicular neoplasm do lobectomy. ( 80% adenoma ) If tumor size > 4 cm in older patients do total thyroidectomy. (risk of malignancy 50%) If there is local invasion, capsular invasion, vascular invasion, LN involvement do -total thyroidectomy (frozen section) -completion thyroidectomy (formal BX) MORTALITY 10-Year survival : 85% 20-Year survival : 70% POOR PROGNOSIS Age > 50 year Tumor size >4cm High tumor grade Marked vascular invasion Extra thyroidal invasion Distant mets HURTHLE CELL TUMORS 3% Subtype of follicular T. cancer Can not be diagnosed by FNAB Characterized by vascular & capsular invasion Contains sheets of eosinophilic cells packed with mitochondria Differ from follicular by : -multifocal & bilateral (30%) -do not take RAI -metastasize to LN (25%) -less 10-year survival (80%) HURTHLE CELL TUMORS TREATMENT ADENOMA: lobectomy INVASIVE CA : total thyroidectomy + central cervical LN removal MEDULLARTY CARCINOMA 5% Male : female (1: 1.5) Age 50-60 years C cells tumor, concentrated in superolateral part of thyroid lobes Presentation –neck mass -pain (common) -palpable cervical LN (20%) -dysphagia, dyspnea, dysphonia -diarrhea due to increase int. motility -cushing syndrome (4%) due to ectopic production of ACTH Distant blood borne mets.. Liver, bone , lung Types -Sporadic (75%) older age, unilateral (80%) -Familial (25%) Familial MTC, MEN2A, MEN2B younger age, bilateral (90%) Secrete Calcitonin, CEA, Serotonin, prostaglandin E2 & F2a, ACTH TREATMENT TOTAL THYROIDECTOMY WITH BILATERAL CENTRAL CERVICAL LN DISSECTION 10-year survival : 35-80 % ANAPLASTIC CARCINOMA 1% Female > male Age 70-80 year Presentation –long standing large mass -rapid enlargement & pain -might be fixed & ulcerated -palpable LN - dysphagia, dyspnea, dysphonia TREATMENT *ISTHMUSECTOMY w/o TRACHEOSTOMY to release tracheal obstruction *THYROIDECTOMY for resectable tumors will add nothing to survival ………………………………………………. Very aggressive tumor, most patients die within 6 months of DX LYMPHOMA < 1% Non-Hodgkins B-cell type Usually isolated but might be a part of generalized disease Usually comes on top of chronic lymphocytic thyroiditis Presentation –painless rapidly enlarging mass -respiratory distress TREATMENT Respond well to -chemotherapy -combined therapy (chemo- radiotherapy) -thyroidectomy + LN resection used only to release airway obstruction Prognosis : 5-year survival ( 50%) METASTATIC CARCINOMA Thyroid is a rare site for metastasis. Usually from kidneys, breast, lungs, melanoma. Thyroidectomy might be helpful if the 1ry is controlable, COMPLICATIONS OF THYROID SURGERY RLN injury - < 1% - RT > LT - treatment : 1ry reapproximation SLN injury (external branch) Cervical sympathetic trunk injury ( Horners syndrome) - in extensive surgery Parathyroid glands injury - transient hypocalcaemia 50% - permanent hypothyroidism < 2% Carotid artery, jugular vein and esophagus injuries infrequent Hematoma Seroma Wound infection NERVE INJURY Unilateral RLN ipsilateral vocal cord paralysis - paramedian position; normal but weak voice. - abducted position; hoarse voice, ineffective cough. Bilateral RLN Bilateral VC paralysis - paramedian position; airway obstruction, voice loss. (?? Tracheostomy) - abducted position; ineffective cough, aspiration, resp. tract inf. Superior LN Inability to tense ipsilateral VC abnormal voice (high notes), voice fatigue. Thank You
