Thyroid Gland Embryology and Anatomy Quiz

Thyroid gland Embryology

• Develops from the median bud of the pharynx at the foramen cecum (junction between anterior two-thirds and posterior third of the tongue)
• Descends in the neck passing close to or through the hyoid bone
• The remaining part of the lobes develop from ultimobranchial body (4th pharyngeal pouch) which gives rise to the superior parathyroid glands
• The inferior parathyroid glands develop from the (3rd pharyngeal pouch)

Thyroid gland Anatomy

• Situated in the neck opposite to the 5th, 6th, & 7th cervical vertebrae. Made up of 2 lobes joined by a thin band of tissues; the isthmus.
• Its apex lies below the oblique line of the thyroid cartilage while the base is at the level of 6th tracheal cartilage
• Covered by true capsule and false capsule from the pretracheal fascia

Thyroid gland Arterial supply

• Superior thyroid artery: The 1st branch of the external carotid artery. Related to the external laryngeal nerve
• Inferior thyroid artery: branch from thyrocervical trunk of subclavian artery. Related to recurrent laryngeal nerve
• Accessory esophageal and tracheal branches
• Thyroid ima (from aortic arch-only in 1-3%)

Thyroid gland Venous drainage

• Superior thyroid vein: into Internal jugular vein
• Middle thyroid vein: into Internal jugular vein
• Inferior thyroid vein: into the left innominate vein

Thyroid gland Lymphatic drainage

• Lateral part: To the upper & lower deep cervical lymph nodes (Levels: II,III,IV,Vb).
• Medial parts of both lobes: 1) Pre-laryngeal LNs over cricothyroid membrane. 2) Pre-tracheal LNs (Delphi). 3) Para-tracheal LNs (mediastinal).

Thyroid gland Related Nerves

• External laryngeal nerve: from sup.Laryngeal from vagus. Supplies cricothyroid + inferior constrictor. Injury: loss of high pitched voice + voice fatigue
• Recurrent laryngeal nerve: from Vagus nerve

Goiter

• Enlargement of the thyroid gland

Goiter Pathophysiology

• Deficiency of Thyroid hormones, either relative or absolute, stimulates the hypothalamus to produce TRH, which in turn stimulate TSH secretion.
• Persistent TSH stimulation leads to diffuse hyperplasia & hypertrophy of the thyroid gland
• If the stress is over, Involution of the gland occurs, and the gland may return to its normal size
• If the stress is persistent, hyperplasia persists → Physiological Goiter
• Sudden fall of TSH, will lead to inactivation of most of the follicles, and the acini become distended with colloid → Colloid goiter
• Fluctuation of TSH levels will lead to cycles of hyperplasia and involution

Thyrotoxicosis

• Is a clinical syndrome in which free T3 or free T4 or both are elevated and peripheral tissues are hypermetabolic, irrespective of the source of the excess hormones
• Etiology: Thyrotoxic goitre, Thyroiditis (Hashimoto thyroiditis/ De Queirvan thyroiditis), Thyrotoxic facticia ( intake of Eltroxin), Functioning thyroid carcinoma, TSH secreting pituitary adenoma, Struma ovarii (ovarian cancer secreting tumor)

Toxic Goiter

• Goitre with increased thyroid hormones
• Either: Diffuse toxic goitre (1ry/Grave’s disease), Toxic nodular goitre (2ry/Plummer’s disease), Toxic adenoma

Primary Toxic Goiter

• Autoimmune disease due to thyroid stimulating antibodies (TSAb). Common in young females (20-30 years)
• Disease has abrupt onset with remission and exacerbation
• 50% of patients have a family hx of autoimmune endocrine disorders
• True exophthalmos is characteristic
• May be complicated by heart failure
• Diffuse thyroid swelling without nodules
• Toxic thyroid profile with high thyroid autoantibodies
• Treatment is mainly medical if failed Surgery or RAI

Primary Toxic Goiter Treatment

• Medical treatment: Antithyroid drugs (Neomercazol/propyl thiouracil), B-blockers, Diazepam
• Surgical treatment: Subtotal thyroidectomy or total thyroidectomy
• RAI: (teratogenic/carcinogenic): Used in old patients (˃ 45 years) after failure of medical treatment or recurrence after thyroidectomy

Thyrotoxic crisis

• Severe postoperative hyperthyroidism due to inadequate preoperative preparation
• Clinical picture: Hyperpyrexia, Hypertension, Delirium & Convulsions.
• Treatment: Cooling + lV (lndral, Corticosteroid, Propylthiouracil, Antipyretics )

Secondary Toxic Goiter

• Occurs in older females (30-50 years)
• On top of long standing nodular goitre. No exophthalmos.
• Thyroid gland is enlarged and nodular. Thyroid hormones are elevated but antibodies are within normal
• Treatment: Surgery after preoperative preparation. RAI might have a role.

Toxic Nodule

• Excess secretion of thyroid hormone from autonomous hyperactive thyroid nodule
• Manifested by thyrotoxic manifestations
• Elevated thyroid hormones, no elevated autoantibodies.
• By U/S: solitary thyroid nodule with increased vascularity
• Thyroid scan : hot nodule with suppression of the uptake of surrounding thyroid tissue.
• Treatment : Surgery & RAI might have a role in elderly

Treatment Based on Patient Age and Goiter Type

• 1ry toxic goiter: > 45yr → Radio iodine. < 45yr → small goiter → Antithyroid drugs. → Large goiter → Surgery.
• 2ry toxic goiter: Surgery
• Toxic nodule: > 45yr → Radio iodine. < 45yr → Surgery (lobectomy or hemithyroidectomy).
• Recurrence after adequate surgery: > 45yr → Ablation by radio iodine. < 45yr → Antithyroid drugs.
• Failure of treatment with antithyroid drugs: Surgery or Radio-iodine

Thyroiditis

• Hashimoto’s thyroiditis: Most common form of thyroiditis, Autoimmune thyroiditis due to anti-thyroglobulin antibodies & thyroid peroxidase antibodies (TPO). Common in middle aged females. Initial manifestations of thyrotoxicosis. Later on →manifestations of myxedema. FNAC is diagnostic. May predispose to Papillary thyroid carcinoma or thyroid lymphoma. Treatment : Medical. Surgical treatment in large goitre, compression manifestations or suspicion of malignancy.

Retrosternal Goitre

• More common in males (tough neck muscles)
• Manifestations is mainly compression manifestations
• Mediastinal syndrome?!
• CT is important
• Treatment is mainly surgical (sternotomy may be required)

Solitary Thyroid Nodule

• May be clinically STN but by U/S reveals MNG (Multinodular goiter)

Solitary Thyroid Nodule Investigation

• Ultrasound
• FNAC
• TFT
• Thyroid scan

Thyroid Gland Disorders

• A 30-year-old female patient presents with neck swelling, intolerance to heat, fast heart rate, sweaty palms, difficulty swallowing and breathing, especially when lying down.
• The swelling in her neck is described as butterfly-shaped, multinodular, and extending to the retrosternal area.
• The swelling moves up with deglutition (swallowing), indicating involvement of the thyroid gland.

Goiter

• Definition: Enlargement of the thyroid gland.

Pathophysiology of Goiter

• Iodine Deficiency: Deficiency of thyroid hormones, either relative or absolute, triggers the hypothalamus to produce TRH, which stimulates TSH secretion.
• Persistent TSH Stimulation: Persistent TSH stimulation leads to diffuse hyperplasia and hypertrophy of the thyroid gland, potentially resulting in:
  • Physiological Goiter: Hyperplasia persists due to continuous stress.
  • Colloid Goiter: Sudden decrease in TSH leads to inactivation of follicles and distension of acini with colloid.
  • Nodular Goiter: Fluctuation of TSH levels causes cycles of hyperplasia and involution, resulting in a mixed pattern with areas of both.

Types of Goiter

• Simple Diffuse Goiter (Physiological Goiter): Common in females, often due to increased body demands (puberty, pregnancy, lactation). Characterized by diffuse, smooth, symmetrical enlargement of the thyroid gland ("Venus Neck").
• Colloid Goiter: Late stage of diffuse hyperplasia with inactive follicles filled with colloid.
• Simple Nodular Goiter: Most common thyroid disease. Occurs due to fluctuations in TSH levels, leading to mixed patterns of active and inactive thyroid follicles. Often presents as a painless neck swelling.

Clinical Features of Goiter

• Common Presentations:
  • Neck swelling
  • Dysphagia (difficulty swallowing)
  • Dyspnea (difficulty breathing)
  • Compression of the trachea or esophagus
  • Hoarseness (due to recurrent laryngeal nerve compression)
  • Symptoms exacerbated when lying down

Investigations for Goiter

• Ultrasound:
  • Assessment of thyroid nodule size and characteristics (TIRADS classification).
  • Assessment of lymph node status.
  • Guidance for fine-needle aspiration cytology (FNAC) for impalpable or small nodules.
• FNAC: Performed if suspicious nodules are identified (based on TIRADS).
• Indirect Laryngoscopy: To evaluate for asymptomatic vocal cord paralysis (occurs in 4% of cases).

Treatment of Goiter

• Indications for Surgery:

  • Suspicion of malignancy
  • Compression symptoms
  • Cosmetic concerns

• Types of Surgery:

  • Hemithyroidectomy: Removal of one lobe of the thyroid gland (for unilateral or localized disease).
  • Subtotal Thyroidectomy: Removal of a significant portion of the thyroid gland (often used for diffuse disease).
  • Near Total Thyroidectomy: Removal of most of the thyroid gland with a small portion left behind.
  • Total Thyroidectomy: Complete removal of the thyroid gland.

• Surgical Approach:

  • Open: Traditional surgical approach with an incision in the neck.
  • Endoscopic: Minimally invasive approach using a small camera and instruments inserted through the mouth.

Thyrotoxicosis

• Definition: A clinical syndrome characterized by elevated free T3 or free T4 levels, leading to hypermetabolism in peripheral tissues.

Causes of Thyrotoxicosis

• Thyrotoxic Goiter: Excess thyroid hormone production due to an enlarged thyroid gland.
• Other Causes:
  • Thyroiditis: Inflammation of the thyroid gland (Hashimoto or De Quervain thyroiditis).
  • Thyrotoxic Facticia: Ingestion of thyroid hormone medication.
  • Functioning Thyroid Carcinoma: Malignant tumor of the thyroid gland producing excess thyroid hormone.
  • TSH-Secreting Pituitary Adenoma: Tumor in the pituitary gland producing excess TSH.
  • Struma Ovarii: Ovarian cancer secreting thyroid hormone.

Types of Thyrotoxic Goiter

• Diffuse Toxic Goiter (Graves' Disease): Autoimmune disease caused by thyroid-stimulating antibodies (TSAb).
• Toxic Nodular Goiter (Plummer's Disease): Occurs in long-standing nodular goiter (due to autonomous nodules).

Clinical Features of Thyrotoxic Goiter

• Primary Toxic Goiter (Graves’ Disease):

  • Common in young females.
  • Abrupt onset with remissions and exacerbations.
  • May be complicated by heart failure.
  • Diffuse thyroid swelling without nodules.
  • Elevated thyroid hormones with high thyroid autoantibodies.
  • Characteristic exophthalmos (bulging eyes).

• Secondary Toxic Goiter (Plummer's Disease):

  • Occurs in older females.
  • Enlarged and nodular thyroid gland.
  • Elevated thyroid hormones but normal thyroid autoantibodies.
  • No exophthalmos.

• Toxic Nodule:

  • Excess thyroid hormone production from an autonomous hyperactive thyroid nodule.
  • Presents with thyrotoxic symptoms and elevated thyroid hormones without elevated autoantibodies.
  • Identified on ultrasound as a solitary nodule with increased vascularity.
  • Thyroid scan shows a "hot" nodule with suppression of uptake in the surrounding thyroid tissue.

Treatment of Thyrotoxic Goiter

• Medical Treatment:
  • Antithyroid drugs: Neomercazol or propylthiouracil (safe during pregnancy).
  • Beta-blockers: To manage tachycardia.
  • Diazepam: For aggressive central nervous system manifestations.
  • Medical treatment can last up to 2 years.
• Surgical Treatment:
  • Subtotal thyroidectomy: Removal of a significant portion of the thyroid gland (often used in patients with Graves' disease).
  • Total thyroidectomy: Complete removal of the thyroid gland (may be necessary for large goiters or recurrent disease).
  • Indications: Failure of medical treatment, recurrent symptoms, compression manifestations.
  • Requires careful preoperative preparation to minimize risk of thyrotoxic crisis.
• Radioactive Iodine (RAI):
  • Used in older patients (>45 years) with failure of medical treatment or recurrent disease after thyroidectomy.
  • Teratogenic and carcinogenic, so use should be carefully considered.

Thyrotoxic Crisis

• Definition: Severe postoperative hyperthyroidism due to inadequate preoperative preparation.
• Clinical Features: High fever, hypertension, delirium, and seizures.
• Treatment: Cooling measures, intravenous administration of medications (Inderal, corticosteroids, propylthiouracil, antipyretics).

Treatment Summary

• Primary Toxic Goiter:
  • >45 years: Radioactive iodine.
  • <45 years:
    • Small goiter: Antithyroid drugs.
    • Large goiter: Surgery.
• Secondary Toxic Goiter: Surgery.
• Toxic Nodule:
  • >45 years: Radioactive iodine.
  • <45 years: Surgery (lobectomy or hemithyroidectomy).
• Recurrence after adequate surgery:
  • >45 years: Ablation with radioactive iodine.
  • <45 years: Antithyroid drugs.
• Failure of treatment with antithyroid drugs: Surgery or radioactive iodine.

Thyroiditis

• Hashimoto's Thyroiditis:
  • Most common form of thyroiditis.
  • Autoimmune thyroiditis with antibodies against thyroglobulin and thyroid peroxidase.
  • Common in middle-aged females.
  • Initial presentation of thyrotoxicosis followed by hypothyroidism (myxedema).
  • Diagnosed by fine-needle aspiration cytology (FNAC).
  • May increase risk of papillary thyroid carcinoma or thyroid lymphoma.
  • Treatment: Medical management, surgery may be considered for large goiters, compression manifestations, or suspicion of malignancy.

Retrosternal Goiter

• More common in males.
• Primarily presents with compression symptoms.
• May cause mediastinal syndrome.
• Important to utilize CT imaging.
• Treatment: Surgical (may require sternotomy).

Solitary Thyroid Nodule

• Key Considerations:
  • Solitary thyroid nodule versus dominant nodule within a multinodular goiter.
  • Clinical assessment may suggest a solitary thyroid nodule, but ultrasound may reveal a multinodular goiter.

Investigation of Solitary Thyroid Nodule

• Ultrasound
• Fine-Needle Aspiration Cytology (FNAC)
• Thyroid Function Tests (TFT)
• Thyroid Scan

Lobes of the Cerebrum

• Frontal Lobe: Controls motor function, responsible for expressive language (Broca's area).
• Temporal Lobe: Processes auditory information and is involved in the interpretation of speech (Wernicke's area).
• Parietal Lobe: Responsible for awareness and processing of somatic sensations like touch, pain, and temperature.
• Occipital Lobe: Processes and analyzes visual stimuli, recognizing and memorizing visual information.

Surgical Anatomy

• Limbic System: Involved in emotions, memory, and behavior.
• Brain Stem: Controls essential functions like breathing, heart rate, and blood pressure.
• Cerebellum: Coordinates movement, balance, and posture.

Blood Supply of the Brain

• Main Arteries: The brain is supplied by the carotid and vertebral arteries.
• Two Brain Supply Systems: Anterior Circulation (carotid arteries) and Posterior Circulation (vertebral arteries).
• Circle of Willis: A critical arterial structure that connects the anterior and posterior circulations, providing alternative pathways for blood flow in case of an obstruction.
• Case Examples:
  • Patient 1: A 71-year-old man with sudden aphasia and lower limb weakness, suggestive of a stroke. Investigated with CT and MRI to identify the location and cause of the stroke, managed conservatively.
  • Patient 2: A 37-year-old man with sudden right hemiparesis likely due to a stroke, diagnosed with CT/CT Angio and MRI. Treated surgically to alleviate pressure and improve blood flow.
  • Patient 3: A 40-year-old man with right-sided paralysis and aphasia, treated within a therapeutic time window with tissue plasminogen activator (tPA) and digital subtraction angiography to identify the location of the blockage.

External Carotid Artery

• Supplies the face, neck, and scalp.
• Branches include: superior thyroid artery, lingual artery, facial artery, and internal maxillary artery.

Venus Drainage

• Venous drainage of brain is through dural sinuses:
  • Superior sagittal sinus: Drains blood from superior portion of brain.
  • Inferior sagittal sinus: Drains blood from inferior portion of brain.
  • Straight sinus: Connects superior and inferior sagittal sinuses.
  • Transverse sinus: Drains blood from lateral portion of brain.
  • Sigmoid sinus: Continues from transverse sinus and drains into internal jugular vein.

Lobes of the Cerebrum

• Frontal Lobe: Contains the motor strip, responsible for voluntary movement.
• Broca's Area: Located in the left frontal lobe, controls expressive language.
• Temporal Lobe: Houses Wernicke's area, responsible for speech comprehension.
• Parietal Lobe: Processes somatic sensation, including touch, pain, and temperature.
• Occipital Lobe: Processes visual stimuli, analyzing, recognizing, and memorizing visual information.

Surgical Anatomy

• Limbic System: Responsible for emotions, memory, and motivation.
• Brain Stem: Controls vital functions like breathing, heart rate, and blood pressure.
• Cerebellum: Coordinates movement, balance, and posture.

Blood Supply of the Brain

• Main Arteries: Carotid and vertebral arteries supply the brain.
• Two Brain Supply Systems: Anterior and posterior circulation systems.
• Circle of Willis: Fusion point of anterior and posterior circulation, ensuring constant blood flow to the brain.

Case Examples

• Case 1: A 71-year-old man experienced sudden aphasia and lower limb weakness. This could be caused by a stroke affecting areas like the middle cerebral artery.
• Case 2: A 37-year-old man had sudden right hemiparesis. CT scans and MRI were used to identify potential causes (like a stroke).
• Case 3: A 40-year-old man had right-sided paralysis and aphasia. CT angiography identified a blocked P2 segment of the left middle cerebral artery.

External Carotid Artery

• Areas of Supply: This artery supplies various areas of the head and face, not primarily the brain.

Venus Drainage

• Blood Drainage: The venous drainage system carries deoxygenated blood from the brain back to the heart.

Test your knowledge on the embryology and anatomy of the thyroid gland. This quiz covers its development, structure, and arterial supply. Ideal for students studying human anatomy or endocrinology.