thyroid gland - part 1

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).


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


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.


Transverse scan of normal thyroid.R, right lobe; L, left lobe; T, trachea


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


Computerised tomography scan of the chest showing a retrosternal goitre with tracheal displacement (arrowed)

Sagital CT section showing goitre filling posterior mediastinum.


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


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


5- PET scan

PET scan may be useful, particularly in localising disease which does not take up radioiodine.


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

thyroid gland - part 1

Health & Medicine

thyroid glandindex

thyroid neoplasmwill

embryologythe thyroid

thyroid diseases6 thyroiditis

antithyroid antibodies

developing thyroid lobes

diagnosis of thyroid

suppressed tsh