Learning objective
By the end of this lesson, learners should be able to describe the anatomical location, vasculature, innervation, and clinical relevance of the thyroid gland, including common congenital anomalies and surgical considerations.
Overview of the thyroid gland
The thyroid gland is an endocrine organ located in the anterior neck that plays a central role in regulating metabolic rate by secreting thyroid hormones.
- Shape: Butterfly-shaped
- Components: Two lateral lobes connected by a central isthmus
- Vertebral levels: Spans C5–T1
Anatomical location
- The lobes wrap around the cricoid cartilage and superior tracheal rings.
- Located within the visceral compartment of the neck, alongside the trachea, oesophagus, and pharynx.
- Enclosed by pretracheal fascia.
Clinical relevance – thyroglossal cyst
- During embryonic development, the thyroid originates near the foramen cecum at the base of the tongue.
- It descends to the anterior neck by week 7, leaving behind the thyroglossal duct, which normally regresses by week 10.
- Persistent duct can form a thyroglossal cyst, typically presenting as:
- Midline neck lump that elevates with tongue protrusion
- Risk of infection or fistula formation
- Management: Complete surgical excision; recurrence ~2.5%
Anatomical relations
- Anterior: Infrahyoid muscles (sternothyroid, superior belly of omohyoid, sternohyoid)
- Lateral: Carotid sheath (common carotid artery, internal jugular vein, vagus nerve)
- Medial: Larynx, pharynx, trachea, oesophagus
- Nerves: External laryngeal nerve, recurrent laryngeal nerve
Vasculature
Arterial supply
- Superior thyroid artery – a branch of the external carotid artery, close to the external branch of the superior laryngeal nerve
- Inferior thyroid artery – a branch of the thyrocervical trunk, near the recurrent laryngeal nerve
- Thyroid ima artery (10% of people) – from the brachiocephalic trunk, supplies the isthmus/anterior surface
Venous drainage
- Superior and middle thyroid veins: drain into the internal jugular vein
- Inferior thyroid vein: drains into the brachiocephalic vein
- Veins form a venous plexus around the gland
Innervation
- Sympathetic branches from the cervical sympathetic trunk
- Function: Regulate vascular tone; hormone secretion is controlled by the pituitary gland
Lymphatic drainage
- Drains to paratracheal nodes and deep cervical lymph nodes
Clinical relevance – recurrent laryngeal nerve
- Lies posteromedially to the thyroid gland, in the tracheoesophageal groove
- Right nerve: loops around the subclavian artery
- Left nerve: loops around the aortic arch
- Injury during thyroid surgery can lead to:
- Hoarseness (unilateral)
- Airway compromise (bilateral)
