Thyroid gland

Anatomy

• Thyroid gland is supplied by superior, inferior thyroid and thyroid ima artery.

• For the Examination of thyroid gland there are various methods e.g Lahey’s method, Crile’s method, Pizillo’s method.

• For thyroid its TIRADS( Thyroid Imaging Reporting and Data System).

• There are different types of thyroid surgeries.

• Hemithyroidectomy in which 1 lobe and isthmus is removed.

• Total thyroidectomy(Removal of whole thyroid gland.)both lobes + isthmus.

• Subtotal thyroidectomy Removal of almost all gland and isthmus except

• 4-8g left on each side.

• Near total thyroidectomy

• Thyroid cancer includes (Differentiated Thyroid cancer) which includes

• Papillary thyroid cancer

• Follicular thyroid cancer

• Hurthle cell thyroid cancer

• Medullary and Anaplastic thyroid cancers.

Causes of hypothyroidism

• Iodine deficiency

• Hashimoto thyroiditis

• Wolf chaikoff effect iodine induced hypothyroidism

• Non functioning pituitary adenoma

• Sheehan syndrome

Causes of hyperthyroidism

• Graves disease

• Solitary toxic nodule

• Jod basedow phenomenon

• TSH secreting pituitary adenoma

Introduction to the Thyroid Gland

According to Love and Bailey’s “A Short Practice of Surgery”, the thyroid gland is one of the most important endocrine organs, regulating metabolism, growth, and development through the production of thyroid hormones.

Embryological Development

• Develops from endoderm of primitive pharynx

• Appears as an epithelial proliferation in the floor of pharynx

• Descends from foramen cecum at tongue base to final position in neck

• Thyroglossal duct normally obliterates by 8-10 weeks gestation

• Parafollicular C-cells derived from neural crest (ultimobranchial body)

Clinical Significance

• Thyroid disorders affect 5-10% of population

• More common in females (4:1 female to male ratio)

• Goiter prevalence: 4-15% in iodine-deficient areas

• Thyroid cancer accounts for 1-2% of all malignancies

Surgical Anatomy of the Thyroid Gland

Gross Anatomy

Capsules of the Thyroid

• True Capsule: Peripheral condensation of fibrous stroma

• False Capsule: Derived from pretracheal fascia

• Surgical Significance:

  • Vessels run between true and false capsules

  • Recurrent laryngeal nerve runs outside true capsule

  • Parathyroids lie between capsules posteriorly

Blood Supply

Venous Drainage

• Superior Thyroid Vein: Drains to internal jugular vein

• Middle Thyroid Vein: Directly to internal jugular vein

• Inferior Thyroid Veins: Form plexus and drain to brachiocephalic veins

Lymphatic Drainage

• Upper pole → Upper deep cervical nodes

• Lower pole → Lower deep cervical, pretracheal, paratracheal nodes

• Isthmus → Pretracheal and prelaryngeal (Delphian) nodes

• Medial portion → Paratracheal nodes

Nerve Supply

Thyroid Physiology

Thyroid Hormone Synthesis

1. Iodide Trapping: Active transport into follicular cells

2. Oxidation: Iodide → Iodine by thyroid peroxidase

3. Organification: Iodination of tyrosine residues on thyroglobulin

4. Coupling: MIT + DIT → T3, DIT + DIT → T4

5. Storage: As colloid in follicular lumen

6. Release: Endocytosis and proteolysis of thyroglobulin

Thyroid Hormones

Regulation of Thyroid Function

• Hypothalamus: TRH (Thyrotropin-releasing hormone)

• Anterior Pituitary: TSH (Thyroid-stimulating hormone)

• Thyroid: T4, T3 production

• Negative Feedback: T4/T3 inhibit TSH and TRH

Functions of Thyroid Hormones

• Metabolism: Increase basal metabolic rate, thermogenesis

• Growth & Development: Essential for CNS development in fetus

• Cardiovascular: Increase heart rate, cardiac output

• Gastrointestinal: Increase gut motility

• Neuromuscular: Maintain normal reflex activity

Thyroid Investigations

Thyroid Function Tests

Imaging Studies

Fine Needle Aspiration Cytology (FNAC)

Benign Thyroid Conditions

Simple Goiter

• Definition: Diffuse enlargement without hyperthyroidism

• Causes: Iodine deficiency, goitrogens, dyshormonogenesis

• Types:

  • Diffuse hyperplastic goiter (early stage)

  • Multinodular goiter (late stage)

• Management:

  • Observation if small and asymptomatic

  • Thyroxine suppression in selected cases

  • Surgery for pressure symptoms, cosmetic concerns

Toxic Goiter

Thyroiditis

Thyroid Nodules

• Prevalence: 4-7% by palpation, 20-76% by ultrasound

• Risk of Malignancy: 5-15% of nodules

• Evaluation: TSH, ultrasound, FNA based on size and features

• Suspicious Features:

  • Microcalcifications

  • Hypoechogenicity

  • Irregular margins

  • Taller-than-wide shape

  • Increased vascularity

Thyroid Malignancies

Classification of Thyroid Cancer

Staging of Thyroid Cancer (TNM System)

Risk Stratification Systems

AMES Classification (for Papillary Cancer)

• Low Risk:

  • All young patients (<41 years)

  • Older patients with: No distant metastases, Minor extathyroid extension, Primary <5cm

• High Risk:

  • Distant metastases

  • Major extathyroid extension

  • Primary >5cm in patients >40 years

MACIS Score (for Papillary Cancer)

Metastasis, Age, Completeness of resection, Invasion, Size

• Score <6: 20-year survival 99%

• Score 6-6.99: 20-year survival 89%

• Score 7-7.99: 20-year survival 56%

• Score ≥8: 20-year survival 24%

Thyroid Surgery

Indications for Thyroid Surgery

Surgical Procedures

Surgical Complications

Postoperative Management

• Immediate:

  • Monitor for bleeding, respiratory distress

  • Check serum calcium at 6-12 hours postop

  • Voice assessment

• Short-term:

  • Thyroid function tests at 4-6 weeks

  • Start thyroxine replacement if total thyroidectomy

  • Wound check at 1-2 weeks

• Long-term (for cancer):

  • Radioactive iodine ablation if indicated

  • Thyroglobulin monitoring

  • Neck ultrasound surveillance

  • TSH suppression therapy

References

• Love, R. J. M., & Bailey, H. (Latest Edition). A Short Practice of Surgery. London: Edward Arnold.

• Chapter on Thyroid and Parathyroid Surgery in Love & Bailey’s textbook

• American Thyroid Association Guidelines

• British Thyroid Association Guidelines

• American Association of Clinical Endocrinologists Guidelines

Key Learning Points from Love & Bailey

“Thyroid surgery requires meticulous technique with thorough knowledge of anatomy, particularly the relationship of the recurrent laryngeal nerve and parathyroid glands. The choice of surgical procedure should be tailored to the specific pathology and patient factors.”

- Love & Bailey, A Short Practice of Surgery

Important Clinical Pearls

• All thyroid nodules require evaluation with TSH and ultrasound

• FNAC is the cornerstone of thyroid nodule evaluation

• Recurrent laryngeal nerve identification is mandatory in thyroid surgery

• Parathyroid glands should be identified and preserved with their blood supply

• Most thyroid cancers have excellent prognosis with appropriate treatment

• Postoperative calcium monitoring is essential after total thyroidectomy

• Multidisciplinary approach is crucial for thyroid cancer management

This educational blog is based on the surgical textbook “A Short Practice of Surgery” by Love and Bailey.

For medical professionals and students only. Always consult current guidelines and local protocols.

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