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Development of the thyroid:

Development of the thyroid In the third week Develops from primitive pharynx and neural crest Median pharyngeal down growth migrates between the first and second arch (marked by foramen caecum of tongue) Passes ventral to the hyoid bone and loops behind it Tract obliterates usually Persistance causes thyroglossal cyst or fistula

Slide 3:

Rarely the thyroid bud fails to descend and develops in situ forming lingual thyroid It may descend to far in the mediastinum causing a primary mediastinum or retrosternal goitre Even thyroid bud may fail to divide in two ,appearing as one lateral bud, left usually being absent

Thyroglossal cyst:

Thyroglossal cyst Most commonly below the hyoid . Evident in teens(lining becomes secretory ) Often has throid tissue inside(some times only thyroid ts ) Cyst along with whole tract ( sistrunks ) is removed to avoid recurrance

Ectopic thyroid tissue:

Ectopic thyroid tissue

aberrant thyroid tissue:

aberrant thyroid tissue tissue located lateral to the jugular vein. This tissue may be found as a nodule attached by connective tissue to the mother gland. These thyroid tissue "islands," which pull away from the visceral body during development, are nevertheless normal. The second site for lateral thyroid tissue is within lymph nodes or their remnants. A cervical lymph node containing thyroid follicles is to be clinically a metastatic thyroid carcinoma. . Always consider the possibility of metastatic thyroid cancer of lateral aberrant thyroid nodules.

Slide 7:

Parafollicular cells scattered between the cubiodal epithelial cells( lining of thyroid follicles) are derived from the neural crest They first migrate to ultimobranchial body of 4 th and 5 th branchial pouches and then to the thyroid They in future life can undergo hyperplastic and maliganant change to form medullary ca

Surgical anatomy of thyroid:

Surgical anatomy of thyroid Situated in anterior traingle of neck Weighs 15 to 20 g. Consists of two lateral lobes and isthmus Small pyramidal lobe of lalouette , of variable size commonly joins the isthmus at its junction with left lateral lobe by a fibrous band or strand of muscle fibre known as levator glandulae thyroidea Extends from middle of thyroid cartilage above to sixth tracheal ring below(5th cervical vertebrae to 1st thoracic vertrebra )

Slide 9:

Measures 5cm in length, 3 cm in width and 2.5 in thickness Condensation of vascular connective tissue k/a suspensory ligament of berry ,binds gland firmly to each side to cricoid cartilage This ligament ,with pretracheal fascia makes thyroid to move up and down during swallowing

Slide 10:

thyroid gland is covered by fascia and laterally by strap muscles and further by sternocleidomastoid False or surgical capsule- pretracheal layer of deep cervical fascia True capsule-peripheral condensation of connective ts of gland

Slide 11:

Its surgical importance is that the musculofascial envelope is incised down the midline ,which is avascular and space between 2 capsules is entered. gland exposed by retracting the strap muscles. nerve supply of these muscles enter laterally . these muscles may be divided transversaly to facilitate access to thyroid. These coverings are sutured in the end of surgery closing the visceral space.

Arterial supply of thyroid:

Arterial supply of thyroid Superior thyroid artery arises as the first branch of external carotid artery , runs downward on inf. Constrictor to reach apex of the lateral lobe,where it divides into larger ant. And smaller post. Branch. ITA arises from thyrocervical trunk and passes upwards for a variable distance before looping down,running medially behind the carotid sheath to reach the posterior lateral aspect of gland at junction of middle and lower thirds.

Slide 13:

Accessory unnamed artery ,most common is thyroidea ima ( neubauer’s artery)originating from the aorta or brachio cephalic trunk, and courses up anteriorly on the trachea to reach the isthmus or one of the lower poles

Venous drainage:

Venous drainage Superior thyroid veins from the upper pole , crosses the CCA, high up in the neck to drain in to internal jugular vein Middle thyroid vein ,overlies ITA , crosses the CCA to end in int. jugular vein(1 st vessel encountered in thyroidectomy ) Inf. Thyroid vein ,descend from isthmus and inf. Poles of lateral lobes ,crossing the CCA , joins into brachiocephalic veins .in the ant. Mediastinum

Recurrant laryngeal nerve:

Recurrant laryngeal nerve the vagus,having entered mediastinum ,gives off RLN , which returns to the neck after encircling the aorta on left and right subclavian artery on right ascends in TE groove and has variable relations with ITA on each side Occasionally it divides early and branches around the artery and is not recurrant in 0.25% cases and passes directly from the vagus to cricothyroid muscle

Slide 17:

The nerve ultimately enters larynx posterior to the cricothyroid articulation ,passing under or through berry’s ligament Supplies intrinsic laryngeal muscles with some sensory supply below the vocal Damage to this nerve u/l -- horsness b/l – stridor

Slide 18:

The RLN may branch in its course in the neck, and identification of a small nerve should alert the surgeon to this possibility. Identification of the nerves or their branches often necessitates mobilization of the most lateral and posterior extent of the thyroid gland, the tubercle of Zuckerkandl , at the level of the cricoid cartilage. The last segments of the nerves often course below the tubercle and are closely approximated to the ligament of Berry. Branches of the nerve may traverse the ligament in 25% of individuals, and are particularly vulnerable to injury at this junction.

Superior laryngeal nerve:

Superior laryngeal nerve Arises from vagus (inferior ganglion)and divides at the level of hyoid bone into large internal nerve and smaller external laryngeal nerve The external branch of the superior laryngeal nerve lies on the inferior pharyngeal constrictor muscle and descends alongside the superior thyroid vessels before innervating the cricothyroid muscle

Relation of STA with SLN(ext. branch):

Relation of STA with SLN(ext. branch) Type 1, The nerve crosses the superior thyroid vessels 1 or more centimeters above a horizontal plane passing the upper border of the superior thyroid pole. Type 2a, Nerve crossing the vessels less than 1 cm above the plane. Type 2b, Nerve crossing the vessel below the plane.

Slide 21:

Damage to this nerve causes palsy of cricithyroid ( tensor of vocal cord) Pitch of voice is altered

Lymphatic drainage:

Lymphatic drainage Rich lymphatic network They drain superiorly into midline delphian nodes ( situated on lower edge of cricoid cartilage),laterally in tracheosophageal nodes, inferiorly in mediastinal nodes.

Slide 23:

Dye studies confirm that majority of lymph from these return to thoracic duct without passing through cervical nodes ,although they may open secondarily Ca may spread to LN out side primary drainage area or contralateral side

Slide 27:

The tubercle of Zuckerkandl is the most posterior extension of the lateral lobes of the thyroid gland at the level of the ligament of Berry \ is closely related to distal portion of RLN


PARATHYROID GLANDS Most individuals have four parathyroid glands, which derive their blood supply primarily from branches of the inferior thyroid artery. Upper parathyroid develops from 4 th branchial pouch Lower from 3 rd branchial pouch Generally, parathyroid glands can be found within 1 cm of the junction of the inferior thyroid artery and the RLN. The superior glands are usually located dorsal to the RLN, whereas the inferior glands are usually found ventral to the RLN

Physiology of thyroid:

Physiology of thyroid The average daily iodine requirement is 0.1 mg, which can be derived from foods such as fish, milk, and eggs, or as additives in bread or salt. In the stomach and jejunum, iodine is rapidly converted to iodide and absorbed into the bloodstream, from where it is distributed uniformly throughout the extracellular space.

Slide 31:

iodide trapping, involves active (ATP-dependent) transport. oxidation of iodide to iodine and iodination of tyrosine residues on Tg , to form monoiodotyrosines (MITs) and diiodotyrosines (DITs). Coupling of two DIT molecules to form tetraiodothyronine or thyroxine ( T 4 ), and one DIT molecule with one MIT molecule to form 3,5,3'-triiodothyronine (T 3 ) Thyroglobulin carrying T 4 and T 3 is then internalized by pinocytosis and digested in lysosomes . Thyroid hormone is released into the circulation, while MIT and DIT are deiodinated and recycled.

Slide 32:

T4 is produced exclusively by thyroid gland but T3 is produced by conversion of T4 to T3 (in liver and stomach)most of the T3 is intracellular Drugs and illness effects the conversion of T4 In cirrohosis ,renal failure and surgery ,T3 deccreases coz of inhibition of conversing enzyme like 5’ monodeiodinase

Slide 33:

Largely bound to protein <0.5% is free T4 bound to globulin( thyroxine binding globulin) T3 bound to transthyrin (thyroxin binding prealbumin ) and albumin. 0.03%T4 is free 0.3% T3 is free

Slide 34:

TSH secretion by the anterior pituitary also is regulated via a negative feedback loop by T 4 and T 3 . Because the pituitary has the ability to convert T 4 to T 3 , the latter is thought to be more important in this feedback control. T 3 also inhibits the release of TRH.


Investigations Blood investigations Radiographic investigation Cytological investigations Nuclear investigations

Blood investigations :

Blood investigations

Slide 37:

Thyroid funt . state TSH(.3-3.3mU/l) Free T4(10-30nmol/l) Free T3(3.5-7.5micromol/l) Euthyroid Normal Normal Normal Thyrotoxic Undetectable High High Myxoedema High Low Low Suppressive T4 therapy Undetectable High High T3 toxicity Low Normal High

Other tests:

Other tests TRH test-a dose of 200 micrograms given. 10 times rise in TSH level in hypothyroidism. No response in hyperthyroidism.

Slide 39:

The thyroid gland also is capable of autoregulation , which allows it to modify its function independent of TSH. As an adaptation to low iodide intake, the gland preferentially synthesizes T3 rather than T4, thereby increasing the efficiency of secreted hormone. In situations of iodine excess, iodide transport, peroxide generation, synthesis, and secretion of thyroid hormones are inhibited.

Slide 40:

Epinephrine and human chorionic gonadotrophin ( hCG ) hormones stimulate thyroid hormone production. In contrast, glucocorticoids inhibit thyroid hormone production. In severely ill patients, peripheral thyroid hormones may be reduced, without a compensatory increase in TSH levels, the sick- euthyroid low T3 syndrome

Thyroid Antibodies :

Thyroid Antibodies Thyroid antibodies include antithyroglobulin (anti- Tg ), antimicrosomal or antithyroid peroxidase (anti-TPO) and thyroid-stimulating immunoglobulin (TSI). They indicate the underlying disorder, usually an autoimmune thyroiditis . Approximately 80% of patients with Hashimoto's thyroiditis have elevated thyroid antibody levels, but levels may also be increased in patients with Graves' disease, multinodular goiter, and, occasionally, with thyroid neoplasms .

Serum Thyroglobulin :

Serum Thyroglobulin Thyroglobulin is not normally released into the circulation in large amounts, but increases dramatically in destructive processes of the thyroid gland, such as thyroiditis or overactive states such as Graves' disease and toxic multinodular goiter. The most important use for serum thyroglobulin levels is in monitoring patients with differentiated thyroid cancer for recurrence, particularly after total thyroidectomy and radioactive iodine ablation.

Radiographic investigations:

Radiographic investigations


ULTRASOUND Ultrasound is an excellent, noninvasive and portable imaging method for studying the thyroid gland, and it has the added advantage of no radiation exposure. However, it cannot be used to image thyroid tissue outside the neck (e.g., to assess the extent of a substernal goiter).

Indications of ultrasound:

Indications of ultrasound Depict accurately the anatomy of the neck in thyroid region Assess the comparative size of nodules, lymph nodes, or goiters in patients who are under observation or therapy Detect a non-palpable thyroid lesion in a patient who was exposed to therapeutic irradiation

Slide 46:

Give very important and clinically useful clues about the likelihood of malignancy Identify the solid component of a complex nodule Facilitate fine needle aspiration biopsy of a nodule Evaluate for recurrence of a thyroid mass after surgery Scrutinize the neonatal thyroid for size and location

Ultrasound characteristics associated with an increased thyroid cancer risk:

Ultrasound characteristics associated with an increased thyroid cancer risk Hypoechoic Microcalcifications Central vascularity Irregular margins Incomplete halo Documented enlargement of a nodule

Slide 48:

Throid swelling or goitre is defined as generalised enlargement of thyroid gland Discrete swelling (solitary nodule) is in one lobe with no palpable abnormality elsewhere Discreate swellings with evidence of abnormality elsewhere in the gland are termed as dominant

Cytological investigations:

Cytological investigations


FNAC Is the first diagnostic test for evaluation of thyroid nodule But its not a replacement of pt. history and examination Is incorrect in 3 % patients


indications Male pt with age <20 or > 70 yrs with rapid nodule growth , recent change in voice Recent irradiation Family history Fixed ,hard nodule with LAP Solitary palpable nodule Dominant nodule in MNG Recent increase in size Cold spot on RAI study


Technique 23 gauge needle and 10 ml syringe Low fowler position with neck extended with pillows under the shoulders Neck turned to left for right nodule Skin cleaned and nodule secured with non dominant hand and needle passed into thyroid nodule When material is seen in hub of needle aspiration stopped and needle withdrawn Repeated for adequate quantity

Slide 54:

If bloody aspirate , smaller 30 gauge needle used and pt repositioned sitting upright or head of bed elevated Aspirated put on clean glass slide , fixed with 95% alcohol US guided FNAC when on small or difficult to palpate nodules ,mixed cystic –solid lesions and multinodular glands

Needle biopsy with ultrasound guidance is generally reserved for:

Needle biopsy with ultrasound guidance is generally reserved for A small nodule in an obese, muscular, or large framed patient. Nodules that are barely palpable or non-palpable Nodule size less than one centimeter. A nodule that is located in the posterior portions of the thyroid gland. A dominant or suspicious nodule within a goiter.

Slide 56:

All nodules that yieled non-diagnostic results on a free-hand biopsy. Complex degenerated nodules if a prior biopsy without ultrasound Incidentalomas that have been detected ultrasonically in patients with high risk factors for thyroid cancer such as exposure to therapeutic x-rays.


results Benign- nodular goiter,lymphocytic thyroiditis , simple cyst, colloid nodule , hyperplastic focus Malignant-papillary , medullary , anaplastic and poorly differentiated thyroid ca,lymphoma and metastatic disease Suspicious-follicular and hurthle cell neoplasm Indeterminate-lack of specific cellular charater Non diagnostic-limited cellularity and poor preservatives

Follicular carcinoma:

Follicular carcinoma

Colloid ( thyroiditis):

Colloid ( thyroiditis )

Lymphocitic thyroiditis:

Lymphocitic thyroiditis

Hurthle cell ca:

Hurthle cell ca

Papillary ca:

Papillary ca

Papillary ca:

Papillary ca

Medullary ca:

Medullary ca


CORE NEEDLE BIOPSY In differentiating follicular and hurthle cell carcinoma Diff. between lymphocytic thyroiditis and thyroid lymphoma Confirm anaplastic ca LA given, small skin incision given Complications haematoma ,dizziness, bleeding and rarely injury to trachea and recurrant laryngeal nerve

Nuclear investigation:

Nuclear investigation


THYROID IMAGING Both iodine -123 ( 123 I) and iodine-131 ( 131 I) are used to image the thyroid gland. Size and shape, distribution of functional activity. Areas that trap less radioactivity than the surrounding gland are termed "cold” whereas areas that demonstrate increased activity are termed "hot." The risk of malignancy is higher in "cold" lesions (15 to 20%) than in "hot" or "warm" lesions (<5%).

Slide 68:

It is usually given orally in a capsule or in liquid form and the quantity accumulated by the thyroid gland at various intervals of time is measured using a gamma scintillation counter. The percentage of RAIU 24 hours after the administration of radioiodide is most useful, since in most instances the thyroid gland has reached the plateau of isotope accumulation, and because it has been shown that at this time, the best separation between high, normal, and low uptake is obtained .

Other tests:

Other tests T 3 suppression test- T3 given orally 40 microgram 8 hourly for 5 days. And than uptake is repeated. Helpful in differentiating thyrotoxicosis from other causes of raised uptake like single goitre due to iodine def. . Less suppression is characteristics of thyrotoxicosis . TSH stimulation test- to distinguish primary from secondary hypothyroidism. In hypopituitarism there will be rise in uptake, with no rise in primary thyroid failure

Increased RAIU:

Increased RAIU Hyperthyroidism (Graves' disease, Plummer's disease, toxic adenoma, trophoblastic disease, pituitary resistance to thyroid hormone, TSH-producing pituitary adenoma) Non-toxic goiter (endemic, inherited biosynthetic defects, generalized resistance to thyroid hormone, Hashimoto's thyroiditis )) Decreased renal clearance of iodine (renal insufficiency, severe heart failure) Recovery of the suppressed thyroid (withdrawal of thyroid hormone and anti-thyroid drug administration, subacute thyroiditis , iodine-induced myxedema ) Iodine deficiency (endemic or sporadic dietary deficiency, excessive iodine loss as in pregnancy or in the dehalogenase defect) TSH administration

Decreased RAIU :

Decreased RAIU Hypothyroidism (primary or secondary) Defect in iodide concentration (inherited "trapping" defect, early phase of subacute thyroiditis , transient hyperthyroidism) Suppressed thyroid gland caused by thyroid hormone (hormone replacement, thyrotoxicosis factitia , struma ovarii ) Iodine excess (dietary, drugs and other iodine contaminants)

Slide 73:

There is inverse relationship between the daily dietary intake of iodine and the RAIU test . The intake of large amounts of iodide (>5 mg/day), mainly from the use of iodine-containing radiologic contrast media, antiseptics, vitamins, and drugs such as amiodarone , suppresses the RAIU values to a level hardly detectable using the usual equipment and doses of the isotope. Depending upon the type of iodine preparation and the period of exposure, depression of RAIU can last for weeks, months, or even years.

Other nuclear scans available:

Other nuclear scans available Technetium-99m ( 99m Tc) pertechnetate is taken up by the thyroid gland and also used for thyroid evaluation. This isotope is taken up by the mitochondria, but is not organified . It also has the advantage of having a shorter half-life and minimizes radiation exposure. It is particularly sensitive for nodal metastases.

Slide 75:

More recently, F- fluorodeoxyglucose positron emission tomography (FDG PET) has been used to screen for metastases in patients with thyroid cancer, in whom other imaging studies are negative. However, this technique is expensive and not widely available

Slide 76:

The test does not measure hormone production and release but merely the avidity of the thyroid gland for iodide and its rate of clearance relative to the kidney. Disease states resulting in excessive production and release of thyroid hormone are most often associated with increased thyroidal RAIU and ( Figuthose causing hormone underproduction with decreased thyroidal RAIU . Important exceptions include high uptake values in some hypothyroid patients and low values in some hyperthyroid patients. Increased thyroidal RAIU with hormonal insufficiency co-occur in the presence of severe iodide deficiency and in the majority of inborn errors of hormonogenesis . Decreased thyroidal RAIU with hormonal excess is typically encountered in the syndrome of transient thyrotoxicosis (both de Quervain's and painless thyroiditis ), 9 ingestion of exogenous hormone ( thyrotoxicosis factitia ), iodide-induced thyrotoxicosis ( Jod-Basedow disease), 10 and in patients with thyrotoxicosis on moderately high intake of iodide . High or low thyroidal RAIU as a result of low or high dietary iodine intake, respectively, may not be associated with significant changes in thyroid hormone secretion.

Causes of thyrotoxicosis:

Causes of thyrotoxicosis Primary hyperthyroidism Graves disease Toxic multinodular goiter Toxic adenoma Thyrotoxicosis without hyperthroidism subacute thyroiditis silent thyoiditis .

Slide 78:

Secondary hyperthyroidism TSH secreting pitutiary adenoma Gestational thyrotoxicosis

Clinical manifestations:

Clinical manifestations Hyperactivity Irritability Heat intolerance and sweating Palpitations , atrial fibrillations Weight loss Tremors Warm and moist hand Lid retraction or lag

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