Thyroid gland

محاظره الجراحه دكتور علي نجم L.1
SURGICAL ANATOMY
The normal thyroid gland weighs 20–25 g. The functioning unit is the lobule supplied by a single arteriole and consists of 24–40 follicles lined with cuboidal epithelium. The follicle contains colloid in which thyroglobulin is stored
The arterial supply is rich, and extensive anastomoses occur between the main thyroid arteries and branches of the tracheal and oesophageal arteries . There is an extensive lymphatic network within the gland
Blood supply of thyroid gland
Superior thyroid artery from external carotid artery right and left
Inferior thyroid artery from thyrocervical trunk right and left
3-10% of population have thyroid ima artery mainly from arch of aorta
Venous drainage
Superior and middle thyroid veins drain directly to the internal jugular vein while the inferior thyroid veins drain via common trunk to the superior vena cava or left brachicephalic vein

Significant nerve relation in thyroid

The superior laryngeal nerve
because of its close relationship to the superior thyroid vessels
Injury to this nerve branch results in bowing of the vocal
cord during phonation. . This effect may go unnoticed except in
individuals, such as singers, who find themselves unable to reach
high-pitched notes or professionals speakers,w ho notice an increased
fatigability of their voice
The recurrent laryngeal nerve
because of its relationship to the inferior thyroid artery it's at risk during surgery so unilateral injury results in paralysis of the vocal cord, which changes the quality of the voice (hoarseness of the voice) while bilateral nerve injury may severely compromise airflow, necessitating tracheostomy


PHYSIOLOGY
Thyroxine
The hormones tri-iodothyronine (T3) and l-thyroxine (T4) are bound to thyroglobulin within the colloid.
Synthesis within the thyroglobulin complex is 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 thyroxine binding 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).
Thyroid hormones play an active regulatory role in many aspects of energy substrate metabolism, including increased oxygen consumption and calorigenesis, stimulation of protein synthesis regulation of most aspects of carbohydrate metabolism, and
metabolism of cholesterol and phospholipids

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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
Investigation in thyroid disorders
TSH: When the serum TSH level is in the normal range, it is redundant
to measure the T3 and T4 levels and the level of( free T3 and T4) is more accurate than plasma level
chest x ray if there is retrosternal extension
ECG for any cardiac problem like arterial fibrillation, tachycardia etc.
FNAC of palpable discrete swellings
ultrasound, CT and MRI scan for known cancer, some reoperations and some retrosternal goiters
isotope scan if discrete swelling and toxicity coexist


HYPOTHYROIDISM
Cretinism (fetal or infantile hypothyroidism)

Cretinism is the consequence of inadequate thyroid hormone

production during fetal and neonatal development
it's either ‘Endemic or sporadic
endemicis due to dietary iodine deficiency, whereas sporadic
cases are due either to an inborn error of thyroid metabolism
or complete or partial agenesis of the gland
A hoarse cry, macroglossia and umbilical hernia in a neonate with features of thyroid failure suggest the diagnosis

Adult hypothyroidism

The term myxoedema should be reserved for severe thyroid
failure and not applied to the much more common mild thyroid deficiency.
The signs of thyroid deficiency are:
• bradycardia
• cold extremities
• dry skin and hair
• periorbital puffiness
• hoarse voice
• bradykinesis, slow movements
• delayed relaxation phase of ankle jerks.
The symptoms are:
• tiredness
• mental lethargy
• cold intolerance
• weight gain
• constipation
• menstrual disturbance
• carpal tunnel syndrome
Delayed relaxation of the ankle jerk reflex is the most useful clinical sign in making the diagnosis
Treatment
Oral thyroxine (0.10–0.20 mg) as a single daily dose is curative
Myxoedema
The signs and symptoms of hypothyroidism are accentuated. The facial appearance is typical, and there is often supraclavicular puffiness, a malar flush and a yellow tinge to the skin


THYROID ENLARGEMENT
The normal thyroid gland is impalpable. The term goitre (from the Latin guttur = the throat) is used to describe generalized enlargement of the thyroid gland. A discrete swelling (nodule) in one lobe with no palpable abnormality elsewhere is termed an isolated (or solitary) swelling. Discrete swellings with evidence of abnormality elsewhere in the gland are termed dominant

Simple goitre Diffuse hyperplastic Physiological

Pubertal
Pregnancy
Multinodular goitre

Toxic Diffuse (Graves’ disease)

Multinodular
Toxic adenoma
Neoplastic Benign
Malignant
Inflammatory