Thyroid Gland Disorders

Thyroid Anatomy & Physiology - Neck's Power Core

• Location: Anterior neck, C5-T1. Two lobes, isthmus; pyramidal lobe (50%).
• Blood Supply:
  • Arteries: Superior Thyroid (from ECA), Inferior Thyroid (from Thyrocervical trunk).
  • Veins: Superior, Middle, Inferior thyroid.
• Nerves:
  • Recurrent Laryngeal N. (RLN) - crucial for voice.
  • Superior Laryngeal N. (SLN) - external branch innervates cricothyroid.
• Microanatomy: Follicles (colloid-filled, T3/T4 via thyroglobulin), Parafollicular C-cells (Calcitonin).
• Physiology: TSH stimulates T3/T4 synthesis (iodine essential). T3 more potent, T4 more abundant. Regulate metabolism, growth.

⭐ The Recurrent Laryngeal Nerve is crucial; its injury during thyroidectomy leads to hoarseness. (Berry's ligament is a key landmark for its identification).

Thyroid Workup - Gland Detective Work

• Initial Blood Tests:
  • TSH (Thyroid Stimulating Hormone): Best initial test, reflects pituitary feedback.
  • Free T4 (Thyroxine), T3 (Triiodothyronine): Assess thyroid function, T4 more stable.
• Antibodies:
  • Anti-TPO Ab: Hashimoto's thyroiditis.
  • Anti-TSHR Ab (TRAb): Graves' disease.
• Imaging:
  • Ultrasound (USG Neck): Initial for nodules, goiter; size, characteristics (solid/cystic), guides FNAC.
  • Radioiodine Uptake (RAIU) & Scan:
    • Hot nodule (↑ uptake): Autonomously functioning, usually benign.
    • Cold nodule (↓ uptake): Non-functioning, higher malignancy risk (approx. 15-20%).
• Cytology:

  ⭐ FNAC (Fine Needle Aspiration Cytology) is the single most important investigation for a thyroid nodule; the Bethesda system for reporting guides management.

Goitre & Hyperthyroidism - Big Neck, Fast Beat

• Goitre: Thyroid gland enlargement (diffuse/nodular). Can be euthyroid, hypo-, or hyperthyroid.
• Hyperthyroidism (Thyrotoxicosis): Clinical state from excess thyroid hormone (TH).
  • Symptoms: Weight loss (despite ↑appetite), heat intolerance, palpitations, anxiety, tremor, ↑bowel frequency.
  • Signs: Tachycardia/AF, goitre, warm moist skin, lid lag/retraction, proptosis (Graves').
• Key Causes:
  • Graves' Disease: Autoimmune.
  • Toxic Multinodular Goitre (TMNG).
  • Toxic Adenoma (Plummer's disease).

⭐ Graves' disease is the most common cause of hyperthyroidism, characterized by diffuse goitre, ophthalmopathy, and often Thyroid Stimulating Immunoglobulins (TSIs) or TRAbs.

• Diagnosis:
  • TSH ↓ (often <0.01 mIU/L), Free T4/T3 ↑.
  • Autoantibodies: TRAb (diagnostic for Graves'), Anti-TPO Ab (often +ve in Graves' & Hashimoto's).
  • Radioiodine Uptake (RAIU) & Scan: Diffuse ↑ uptake (Graves'); focal ↑ (hot nodule in toxic adenoma); multiple areas of ↑ & ↓ uptake (TMNG).
• Management Principles:
  • Beta-blockers (e.g., Propranolol) for symptomatic relief.
  • Anti-thyroid drugs (ATDs): Methimazole (MMI), Propylthiouracil (PTU - preferred in 1st trimester pregnancy, thyroid storm).
  • Radioactive Iodine (RAI) ablation (I-131).
  • Thyroidectomy (subtotal/total).

Thyroid Neoplasms & Post-Op Complications - Cancer & Aftercare

• Malignancies (FNA Diagnosed):
  • Papillary (PTC): ~80%, Orphan Annie eyes, psammoma bodies, BRAF mutation. Lymphatic spread.
  • Follicular (FTC): ~10%, RAS mutation. Hematogenous spread.
  • Medullary (MTC): ~5%, from C-cells, ↑Calcitonin (marker), RET proto-oncogene (MEN2). Amyloid stroma.
  • Anaplastic: <2%, aggressive, elderly, poor prognosis, often unresectable.
• Treatment Pathway: Primarily surgical, followed by:

> ⭐ **Papillary Thyroid Carcinoma (PTC)** is the most common thyroid malignancy, known for excellent prognosis and characteristic Orphan Annie eye nuclei and psammoma bodies on histology.

• Key Post-Op Complications:
  • Hypocalcemia (parathyroid injury): Tingling, Chvostek's. Monitor serum $Ca^{2+}$.
  • Recurrent Laryngeal N. (RLN) injury: Hoarseness (unilateral).
  • Superior Laryngeal N. (SLN) injury: Voice fatigue, ↓pitch range.
  • Hemorrhage/Hematoma: Airway risk.

High‑Yield Points - ⚡ Biggest Takeaways

• Papillary carcinoma: most common thyroid cancer; shows Orphan Annie eyes, psammoma bodies.
• Medullary carcinoma: from C-cells, secretes calcitonin; linked to MEN 2A/2B.
• FNAC: gold standard for investigating thyroid nodules.
• Recurrent laryngeal nerve injury: commonest in thyroidectomy, causes hoarseness.
• Graves' disease: most common cause of hyperthyroidism; diffuse goiter, exophthalmos.
• Thyroid storm: emergency; manage with PTU/methimazole, propranolol, iodine, steroids.
• Anaplastic carcinoma: elderly, rapid growth, poor prognosis.