thyroid gland - part 1
DESCRIPTION
Thyroid gland ( historical background - embryology - anatomy - physiology - evaluation of the thyroid disorders - and thyroiditisTRANSCRIPT
THYROID GLAND
ZIYAD SALIH
Al-Qadisiya Collage Of Medicine6th Stage
THYROID GLANDIndex :-1- Historical Background2- Embryology3- Anatomy4- physiology5- Evaluation of Patient with thyroid diseases6- THYROIDITIS--------------------------------------------------------------Hypo-Hyper-thyroidism & Thyroid neoplasm Will be discussed in the next week
Historical Background The term thyroid
gland (Greek thyreoeides, shield-shaped)
however, attributed to Thomas Wharton in his Adenographia at 1656
In 1776, the thyroid was classified as a ductless glandby Albrecht von Haller and was thought to have numerous functionsranging from lubrication of the larynx to acting as a reservoirfor blood to provide continuous flow to the brain, and tobeautifying women’s necks.
Embryology
The thyroid gland arises as an out pouching of the primitiveforegut around the third week of gestation. It originates at thebase of the tongue at the foramen cecum.The developing thyroid lobes arising in the fourth pharyngeal pouch , while the isthmus arise from Third pharyngeal pouch
Embryology With further development, the thyroid
descends into the neck anterior to the hyoid bone and laryngeal cartilages.
Certain congenital anomalies such as ectopic thyroid tissue or thyroglossal duct cysts are directly related to this embryologic descent.
The parafollicular cells, or C cells, are derived from the neural crest, migrate to the thyroid, and produce calcitonin.
Embryology
The descent of theThyroid , showing possible sites ofectopic thyroid tissue or thyroglossalcysts, and also the course of athyroglossal fistula. The arrow showsthe further descent of the thyroid thatmay take place retrosternally into thesuperior mediastinum.
Thyroid Anatomy
The normal thyroid gland weighs 20–25 g. The functioning unit isthe lobule supplied by a single arteriole and consisting of 24–40follicles lined with cuboidal epitheliumFormed of 2 lobes (Rt & Lt), that are connected by band of tissue called “isthmus”.
The blood supply to the thyroid arises from two pairs of main arteries: the superior thyroid artery (branch of theexternal carotid) and the inferior thyroid artery (branch of the thyro-cervical trunk). A thyroidea ima artery arises directly from the aorta or innominate in 1% to 4% of individuals to enter the isthmusVenous return :-The superior thyroid veins & The middle vein . The superior and middle veins drain directly into the internal jugular veins. The inferior veins often form a plexus, which drains into the brachiocephalic veins
The recurrent laryngeal nerve (RLN) usually courses 1 cm anterior or posterior to the inferior thyroid artery. Careful dissection around this artery is necessary to avoid injury to the RLN.
Lymphatic Drainage1- direct to deep cervical L.N2- sub capsular plexuses :-A- juxtathyroid node ( Delphian ) centrally locatedB- pretracheal L.NC- L.N along the veins3- The drain to deep cervical and mediastainal L.N
The thyroid gland is concerned with the synthesis of the iodine - containing hormones thyroxine (tetra - iodothyronine, T4) and tri – iodothyronine (T3) , which control the metabolic rate of the body;
T3 is the active hormone, and T4 is converted to
T3 in the periphery .The thyroid gland also secretes calcitonin from the parafollicular C cells, which reduces the level of serum calcium and is therefore antagonistic to parathormone.
Thyroid physiology
The immediate control of synthesis and
liberation of T3 and T4 is by
thyroid - stimulating hormone
(TSH) produced by the anterior pituitary.
TSH is secreted in response to the level of
thyroid hormones in the blood by
a negative feedback mechanism.
The secretion of TSH is also under
The influence of the
hypothalamic -thyrotrophin -
releasing hormone ( TRH )
Physiological control of secretion
1- History ( discuss in each topic )2- examination 3- Biochemical tests4- Radiological tests5- FNAC6- Core Biopsy7- laryngoscope
Evaluation of thyroid disorders
1- Measurement of TSH (0.3 to 5 mIU/L) is the most useful biochemical test in the diagnosis of thyroid illness. In most patients without pituitary disease, increased TSH signifies hypothyroidism, suppressed TSH suggests hyperthyroidism, and normal TSH reflects a euthyroid state
2 -Assessment of free T 4 (4.5 to 11.2 μg/dL) concentration supports identified abnormalities in TSH and provides an index of severity of illness.
Biochemical Evaluation of thyroid disorders
3 -Measurement of T 3 (80 to 200 ng/dL) is unreliable as a test for hypothyroidism. This test is useful in the occasional patient with suspected hyperthyroidism, suppressed TSH, and normal T4 (T3 thyrotoxicosis).
4 -Anti-thyroid antibodies are found in the serum of patients with autoimmune thyroiditis (Hashimoto thyroiditis) .
5 -Anti-TSH receptor antibodies, which stimulate the TSH receptor, are detectable in more than 90% of patients with autoimmune hyperthyroidism (Graves' disease).
Biochemical Evaluation of thyroid disorders
Biochemical Evaluation of thyroid disorders
1- Chest X-ray 2- Ultrasound 3- CT & MRI 4- Isotope scan
5- PET scan
Chest and thoracic inlet radiograph
Simple radiographs of the chest and thoracic inlet will rapidly and economically confirm the presence of significant retrosternal goitre and clinically important degrees of tracheal deviation and compression. Pulmonary metastases may also be detected
Radiological Evaluation of thyroid disorders
1- Chest X-ray 2- Ultrasound 3- CT & MRI 4- Isotope scan
5- PET scan
Ultrasound scanning
High-frequency ultrasound scanning gives good anatomical images of the thyroid and surrounding structures but, unfortunately , reveals more thyroid swellings than are clinically relevant. After a period of years the ultrasound is enjoying a revival as a means of reducing the number of unsatisfactory aspiration cytology samples; it permits more targeted sampling, allowing the identification of parathyroid adenomas and nodes involved in thyroid cancer.
Radiological Evaluation of thyroid disorders
Transverse scan of normal thyroid.R, right lobe; L, left lobe; T, trachea
1- Chest X-ray 2- Ultrasound 3- CT & MRI 4- Isotope scan
5- PET scan
Computerised tomography & magnetic resonance imaging
These are not indicated for thyroid swellings and are reserved for the assessment of known malignancy and to assess the extent of retro-sternal and, occasionally, recurrent goitres. The appearance of a retro-sternal goitre on CT can give a misleading impression of the operative difficulty in delivery through a neck incision
Radiological Evaluation of thyroid disorders
Computerised tomography scan of the chest showing a retrosternal goitre with tracheal displacement (arrowed)
Sagital CT section showing goitre filling posterior mediastinum.
1- Chest X-ray 2- Ultrasound 3- CT & MRI 4- Isotope scan
5- PET scan
Isotope scanning
The uptake by the thyroid of a low dose of either radiolabelled
iodine (123I) or the cheaper technetium (99mTc) will demonstrate
the distribution of activity in the whole gland. Routine isotope
scanning is unnecessary and inappropriate for distinguishing
benign from malignant lesions because the majority (80%) of ‘cold’swellings are benign and some (5%) functioning or ‘warm’ swellings
will be malignant. Its principal value is in the toxic patient with a
nodule or nodularity of the thyroid. Localisation of overactivity in
the gland will differentiate between a toxic nodule with suppression
of the remainder of the gland and toxic multinodular goitre
Radiological Evaluation of thyroid disorders
Technetium thyroid scan showing a ‘cold’ nodule that does not take up isotope expanding the left thyroid lobe
Technetium thyroid scan showing appearance of a 1-cm
1- Chest X-ray 2- Ultrasound 3- CT & MRI 4- Isotope scan
5- PET scan
PET scan may be useful, particularly in localising disease which does not take up radioiodine.
Radiological Evaluation of thyroid disorders
is the investigation of choice for discrete thyroid swellings. FNAC has excellent patient compliance, is simple and quick to perform in the out-patient department and is readily repeated. FNAC results should be reported using standard terminology. There is a trend to use ultrasound to guide the needle to achieve more accurate sampling and reduce the rate of unsatisfactory aspirates
Fine-needle aspiration cytology (FNAC)
Classification of fine-needle aspiration cytology reportsThy1 = Non-diagnostic
Thy2 = Non-neoplastic
Thy3 = Follicular
Thy4 = Suspicious of cancer
Thy5 = Malignant
Fine-needle aspiration cytology (FNAC)
Core biopsy gives a strip of tissue for histological rather than
cytological assessment. It has a high diagnostic accuracy but
requires local anaesthesia, and may be associated with complications
such as :- pain, bleeding, tracheal and recurrent laryngeal
nerve damage.
Core biopsy
Flexible laryngosopy is widely used preoperatively to determine the mobility of the vocal cords, although usually for medicolegal rather than clinical reasons.
Nevertheless, the presence of a unilateral cord palsy coexisting with a swelling suggestive of malignancy is usually diagnostic.
Laryngoscope
Laryngoscope
Thyroiditis is a group of autoimmune and inflammatory disorders characterized byinfiltration of the thyroid with inflammatory cells and subsequent fibrosis of the gland..
THYROIDITIS
Autoimmune thyroiditisis a chronic autoimmune disorder characterized by destructive
lymphocytic infiltration of the thyroid.
The disease is 15 times more common in women, and more than 90% of patients have circulating antibodies directed against
thyroid microsomes and thyroglobulin.
THYROIDITIS
Autoimmune thyroiditisAlthough patients initially are euthyroid,
hyperthyroidism and hypothyroidism may occur later.
Thyroid hormone is given to hypothyroid patients both as replacement therapy and to suppress TSH.
Thyroidectomy is indicated for :-
1- compressive symptoms,
2- a dominant nodule
3- suspicious for malignancy,
4- or cosmetic preference.
THYROIDITIS
Acute suppurative thyroiditis
is rare and caused by pyogenic infection withStreptococcus or Staphylococcus species. Treatment consists of appropriate antibiotic therapy and surgical drainage of abscesses. Long-term effects on thyroidfunction are uncommon.
THYROIDITIS
Subacute (de Quervain) thyroiditis
is a rare condition that occurs in young women,often after a viral upper respiratory tract infection.Symptoms include fatigue, weakness, and painful thyroid enlargement radiating tothe patient's jaw or ear
THYROIDITIS
Subacute (de Quervain) thyroiditis
Fine needle aspiration (FNA) can be diagnostic with the identification of giant cells. Treatment with non steroidal anti-inflammatory drugs or steroids can alleviate symptoms. The condition almost always remits spontaneouslywithin a few weeks.
THYROIDITIS
Riedel's thyroiditis
is a rare, progressive inflammatory condition of theentire thyroid gland, strap muscles, and other neck structures. Its cause is unknown, and it can be associated with other fibrotic processes, includingretroperitoneal fibrosis, sclerosing cholangitis, and fibrosing mediastinitis
THYROIDITIS
Riedel's thyroiditis
Riedel's thyroiditis may require surgical excision to exclude malignancy or relieve compressive symptoms on the trachea or esophagus.
THYROIDITIS