THE THYROID AND THE THYROID AND PARATHYROID GLANDSPARATHYROID GLANDS

EMBRYOLOGYEMBRYOLOGY

The thyroglossal of the duct develops from the The thyroglossal of the duct develops from the median bud of the pharynx.median bud of the pharynx.

The foramen caecum at the base of tongue is the The foramen caecum at the base of tongue is the vestigial remnant of the duct.vestigial remnant of the duct.

The parathyroid glands develop from the 3The parathyroid glands develop from the 3rdrd and 4 and 4thth pharyngeal pouches.pharyngeal pouches.

The thymus develops from the 3The thymus develops from the 3rdrd pouch. pouch. The developing thyroid lobes amalgamate with the The developing thyroid lobes amalgamate with the

structures arising in the 4structures arising in the 4thth pharyngeal pouch i.e. the pharyngeal pouch i.e. the superior parathyroid gland and ultimobrachial body.superior parathyroid gland and ultimobrachial body.

Parafollicular cells ( C cells ) from the neural crest Parafollicular cells ( C cells ) from the neural crest reach the thyroid via ultimobrachial body.reach the thyroid via ultimobrachial body.

SURGICAL ANATOMY OF THYROIDSURGICAL ANATOMY OF THYROID

The normal thyroid gland The normal thyroid gland weighs 20-25 g.weighs 20-25 g.

The functioning unit is the The functioning unit is the lobule supplied by a single lobule supplied by a single arteriole and consisting of 24-arteriole and consisting of 24-40 follicles lined with cubidal 40 follicles lined with cubidal epithelium.epithelium.

The follicle contains colloid in The follicle contains colloid in which thyroglobulin is stored. which thyroglobulin is stored. The arterial supply is rich and The arterial supply is rich and extensive anastomosis occur extensive anastomosis occur between the main thyroid between the main thyroid arteries and branches of the arteries and branches of the tracheal and esophageal tracheal and esophageal arteries.arteries.

There is an extensive There is an extensive lymphatic network within lymphatic network within gland. gland.

SURGICAL ANATOMY OF PARATHYROID SURGICAL ANATOMY OF PARATHYROID GLANDGLAND

The normal parathyroid gland The normal parathyroid gland weighs upto 50 mg.weighs upto 50 mg.

These are orange/brown in These are orange/brown in colour.colour.

Most adults have 4 parathyroid Most adults have 4 parathyroid glands.glands.

The superior parathyroid is The superior parathyroid is more consistent in position than more consistent in position than the inferior.the inferior.

The superior gland is commonly The superior gland is commonly found in fat above the inferior found in fat above the inferior thyroid artery and close to the thyroid artery and close to the cricothyroid articulationcricothyroid articulation

PHYSIOLOGYPHYSIOLOGY

The hormones T3 and T4 are bound to the The hormones T3 and T4 are bound to the thyroglobulin with in the colloid .thyroglobulin with in the colloid .

Synthesis with in the thyroglobulin complex is Synthesis with in the thyroglobulin complex is controlled by several enzymes in distinct steps:controlled by several enzymes in distinct steps:

- Trapping of inorganic iodide from the blood.- Trapping of inorganic iodide from the blood.

- Oxidation of iodide to the iodine.- Oxidation of iodide to the iodine.

- Binding of iodine with tyrosine to form - Binding of iodine with tyrosine to form iodotyrosines.iodotyrosines.

- Coupling of monoiodotyrosines and di-- Coupling of monoiodotyrosines and di-iodotyrosines to form T3 and T4 iodotyrosines to form T3 and T4

The metabolic effects of the thyroid The metabolic effects of the thyroid hormones are due to unbound freeT3 and hormones are due to unbound freeT3 and T4.T4.

T3 and T4 are 0.3% and 0.03% of the total T3 and T4 are 0.3% and 0.03% of the total circulating hormones respectively.circulating hormones respectively.

T3 is more important physiological T3 is more important physiological hormone. It is quick acting( with in few hormone. It is quick acting( with in few hours) where as T4 acts more slowly ( 4-14 hours) where as T4 acts more slowly ( 4-14 days ) days )

PARATHYROID HORMONEPARATHYROID HORMONE

It is 84-amino acid peptide.It is 84-amino acid peptide. It controls the level of serum calcium or high serum It controls the level of serum calcium or high serum

magnesium level.magnesium level. It activates osteoclasts to resorb bone and increases It activates osteoclasts to resorb bone and increases

calcium reabsorption from urine and renal activation calcium reabsorption from urine and renal activation of vitamin D.of vitamin D.

CALCITONINCALCITONIN

Parafollicular cells of thyroid are neuroendocrine Parafollicular cells of thyroid are neuroendocrine origin and arrive in the thyroid via ultimobrachial origin and arrive in the thyroid via ultimobrachial body.body.

These produce calcitonin which is serum marker for These produce calcitonin which is serum marker for recurrence of medullary thyroid cancer. recurrence of medullary thyroid cancer.

THE PITUITARY –THYROID AXISTHE PITUITARY –THYROID AXIS

The synthesis and liberation The synthesis and liberation of thyroid hormones from of thyroid hormones from the thyroid is controlled by the thyroid is controlled by TSH from anterior pituitary TSH from anterior pituitary gland.gland.

Secretion of TSH depends Secretion of TSH depends upon the level of circulating upon the level of circulating thyroid hormones and is thyroid hormones and is modified in a classic modified in a classic negative feedback manner.negative feedback manner.

Regulation of TSH secretion Regulation of TSH secretion also results from the action also results from the action of TRH produced in the of TRH produced in the hypothalamus.hypothalamus.

TESTS OF THYROID FUNCTIONTESTS OF THYROID FUNCTION

SERUM TSH:SERUM TSH: Normal value: o.3-3.3 mU/L.Normal value: o.3-3.3 mU/L. In euthyroid state T3,T4 and TSH levels will all be within In euthyroid state T3,T4 and TSH levels will all be within

normal range.normal range. Incipient or developing thyroid failure is characterised Incipient or developing thyroid failure is characterised

by low normal values of T3 and T4 and elevation of TSH.by low normal values of T3 and T4 and elevation of TSH. In toxic states the TSH level is suppressed and In toxic states the TSH level is suppressed and

undetectable.undetectable.

SERUM T3 and T4:SERUM T3 and T4: Normal values:T3=3.5-7.5 mic mol/L T4=10-30 n mol/L.Normal values:T3=3.5-7.5 mic mol/L T4=10-30 n mol/L. Highly accurate radioimmunoassay of free T3 and T4 are Highly accurate radioimmunoassay of free T3 and T4 are

now routine.now routine.

CHEST AND THORACIC INLET CHEST AND THORACIC INLET RADIOGRAPHYRADIOGRAPHY

It shows presences of significant retrosternal goiter.It shows presences of significant retrosternal goiter. It is clinically important for degree of tracheal It is clinically important for degree of tracheal

deviation and compression.deviation and compression. Pulmonary metastasis may also be detected.Pulmonary metastasis may also be detected.

ULTRSOUND SCANINGULTRSOUND SCANING

- It gives good - It gives good anatomical images of anatomical images of the thyroid and the thyroid and surrounding surrounding structures.structures.

- It permits more - It permits more targeted sampling, targeted sampling, allowing the allowing the identification of identification of parathyroid adenomas parathyroid adenomas and nodes involved in and nodes involved in thyroid cancer.thyroid cancer.

ISOTOPE SCANNINGISOTOPE SCANNING

It distinguish benign from malignant lesions.It distinguish benign from malignant lesions. 80% of cold swellings are benign and 5% functioning 80% of cold swellings are benign and 5% functioning

or warm swellings are malignant.or warm swellings are malignant. Localization of overactivity in the gland will Localization of overactivity in the gland will

differentiate between a toxic nodule with suppression differentiate between a toxic nodule with suppression of the remainder of the gland and toxic multinodular of the remainder of the gland and toxic multinodular goitre goitre

FINE NEEEDLE ASPIRATION CYTOLOGYFINE NEEEDLE ASPIRATION CYTOLOGY

It is the investigation of It is the investigation of choice for discrete thyroid choice for discrete thyroid swellings.swellings.

It is simple and quick to It is simple and quick to perform.perform.

Ultrsound guided FNAC is Ultrsound guided FNAC is perfomed to achieve more perfomed to achieve more accurate sampling.accurate sampling.

HYPOTHYROIDISMHYPOTHYROIDISM

CLASSSIFICATION OF HYPOTHYROIDISM:CLASSSIFICATION OF HYPOTHYROIDISM: Autoimmune thyroiditisAutoimmune thyroiditis

Non-goitrous: primary myxoedemaNon-goitrous: primary myxoedema

Goitrous: Hashimoto’s Goitrous: Hashimoto’s IatrogenicIatrogenic

After thyroidectomyAfter thyroidectomy

After radioiodine therapyAfter radioiodine therapy

Drug induced( anti thyroid drugs,para aminosalicylic Drug induced( anti thyroid drugs,para aminosalicylic acid and iodides in excess)acid and iodides in excess)

DyshormonogenesisDyshormonogenesis GoitrogensGoitrogens Secondary to pituitary or hypothalamic diseaseSecondary to pituitary or hypothalamic disease Thyroid agenesisThyroid agenesis Endmic cretinismEndmic cretinism

Often goitrois and due to iodine deficiency.Often goitrois and due to iodine deficiency.

CRETINISMCRETINISM

It is the consequence of It is the consequence of inadequate thyroid hormone inadequate thyroid hormone production during fetal and production during fetal and neonatal development.neonatal development.

““Endemic cretinism” is due to Endemic cretinism” is due to dietary deficiency, where as dietary deficiency, where as sporadic are due to inborn sporadic are due to inborn error of thyroid metabolism error of thyroid metabolism or complete or partial or complete or partial agenesis of the gland.agenesis of the gland.

CLINICAL FEATURES:CLINICAL FEATURES: A hoarse cryA hoarse cry MacroglossiaMacroglossia Umbilical herniaUmbilical hernia

TREATMENT:TREATMENT: Thyroxine with in few days of birth are Thyroxine with in few days of birth are

essential to prevent damage in utero essential to prevent damage in utero progressing and if physical and mental progressing and if physical and mental development are to be normal.development are to be normal.

ADULT HYPOTHYROIDISMADULT HYPOTHYROIDISM

SYMPTOMS:SYMPTOMS: TirednessTiredness Mental lethargyMental lethargy Cold intoleranceCold intolerance Weight gainWeight gain ConstipationConstipation Mental disturbanceMental disturbance Carpal tunnel syndromeCarpal tunnel syndrome

SIGNS:SIGNS: BradycardiaBradycardia Cold extremitiesCold extremities Dry skin and hair Dry skin and hair Periorbital puffinessPeriorbital puffiness Hoarse voiceHoarse voice Bradykiesis, slow movementsBradykiesis, slow movements Delayed relaxation phase of ankle jerksDelayed relaxation phase of ankle jerks

INVESTIGATIONS:INVESTIGATIONS: T3 and T4 are decreased.T3 and T4 are decreased. TSH is increased.TSH is increased.

TREATMENT:TREATMENT: Oral thyroxine (0.10-0.20 mg) as a single Oral thyroxine (0.10-0.20 mg) as a single

daily dose is curative.daily dose is curative. In elderly and cardiac patients replacement In elderly and cardiac patients replacement

dose is commenced at 0.05 mg daily and dose is commenced at 0.05 mg daily and increased cautiously.increased cautiously.