Anatomy of Thyroid Gland

🧠 Anatomy of the Thyroid Gland

The thyroid gland is a highly vascular, ductless endocrine gland with several unique anatomical and physiological features.

In this post, we’ll cover its location, parts, coverings, blood supply, lymphatic drainage, nerve supply, and important clinical correlations.

📍 Location of the Thyroid Gland

• Located anterior to the upper trachea, opposite C5–T1 vertebrae.

• Lateral lobes extend from the middle of the thyroid cartilage to the 4th or 5th tracheal ring.

• Isthmus lies opposite the 2nd to 4th tracheal rings.

🔹 Parts of the Thyroid Gland

• 2 lateral lobes
• Isthmus connecting the lobes
• Pyramidal lobe (in 50–60% of individuals)
• Zuckerkandl's tubercle (in ~60% individuals)

📏 Size and Weight

• Each lobe:

  • Length: 5 cm
  • Width: 3 cm
  • Depth (A-P): 1.5 cm

• Average weight: 20–25 g (larger in females)

• Increases during menstruation and pregnancy

🧥 Capsules of the Thyroid

• True Capsule: Peripheral condensation of the fibrous stroma.

• False Capsule: Derived from pretracheal fascia.

What is the clinical significance of the thyroid capsules?

Why does thyroid swellings move up and down with degluttition?

📌 Berry’s Ligament (Suspensory Ligament)

• Thickening of the pretracheal fascia.
• Attaches posteromedial surface of the lobe to the cricoid cartilage and upper tracheal rings.

What is the clinical significance of Berry’s Ligament?

🧭 Surfaces, Borders & Relations

🔼 Apex

• Points upward and laterally

• Lies between:

  • Inferior constrictor (medial)
  • Sternothyroid (lateral)

• Related to:

  • Superior thyroid artery (superficial)
  • External laryngeal nerve (deep)

Where should you ligate Superior thyroid artery in Thyroidectomy?

🔽 Base

• Extends to 5th/6th tracheal ring

• Related to:

  • Inferior thyroid artery
  • Recurrent laryngeal nerve

Where should you ligate Inferior thyroid artery in Thyroidectomy?

🟪 Anterolateral Surface

Overlapped by (from deep to superficial):

• Sternothyroid
• Sternohyoid
• Superior belly of omohyoid
• Sternocleidomastoid

🔷 Medial Surface

• 2 Tubes: Larynx & Trachea, Pharynx & Esophagus
• 2 Muscles: Inferior constrictor, Cricothyroid
• 2 Nerves: External laryngeal, Recurrent laryngeal

🟩 Posterolateral Surface

• Related to carotid sheath and contents

🔸 Anterior Border

• Relation: Anterior branch of superior thyroid artery

🔹 Posterior Border

• Anastomosis of superior & inferior thyroid arteries
• Parathyroid glands
• Thoracic duct (on left)

🔗 Isthmus of Thyroid Gland

• Dimensions: 1.25 × 1.25 cm

• Anterior Relations: Sternothyroid, sternohyoid, fascia, anterior jugular vein, skin

• Posterior Relation: 2nd to 4th tracheal rings

• Lower Border: Inferior thyroid veins, thyroidea ima artery (if present)

• Upper Border:

  • Anastomosis of superior thyroid arteries
  • Pyramidal lobe (remnant of thyroglossal duct)
  • Tubercle of Zuckerkandl

What is Pyramidal lobe? What is its clinical importance?

What is Tubercle of Zuckerkandl? What is its clinical importance?

🩸 Arterial Supply of Thyroid Gland

💉 Venous Drainage of Thyroid Gland

🧬 Lymphatic Drainage of Thyroid Gland

• Lateral gland → Level III, IV (jugular nodes), sometimes Level V

• Medial gland → Level VI (prelaryngeal, pretracheal, paratracheal)
  → then to Level VII (anterior mediastinal nodes)

⚡ Nerve Supply of Thyroid Gland

Closely Related Nerves:

• Recurrent laryngeal nerve
• External branch of superior laryngeal nerve

How is the Recurrent laryngeal nerve related to the thyroid gland?

What will injury to the Recurrent laryngeal nerve present as?