Venous Drainage of the Thyroid Gland

Three Pairs of Thyroid Veins

Venous drainage is via three pairs of veins that form a venous plexus on the surface (and in the substance) of the gland before draining into the larger veins of the neck.

Vein	Drains From	Drains Into
Superior thyroid vein	Upper pole of lateral lobe	Internal jugular vein (after joining the facial vein or directly)
Middle thyroid vein	Middle of the lateral lobe	Internal jugular vein directly
Inferior thyroid veins	Lower pole and isthmus	Left brachiocephalic vein (both sides drain left, though the right may drain into the right brachiocephalic vein)

Key Features

Superior Thyroid Vein

• Accompanies the superior thyroid artery
• Drains into the common facial vein or directly into the internal jugular vein
• Paired (one on each side)

Middle Thyroid Vein

• Has no accompanying artery — important distinguishing feature
• Short, wide vein passing directly laterally to drain into the internal jugular vein
• Must be ligated early during thyroidectomy to mobilise the lobe

Inferior Thyroid Veins

• Most variable in number and course — may be two, three, or four veins
• Drain downward from the lower pole and isthmus, forming a plexus (thyroid plexus) in front of the trachea
• Both left and right inferior thyroid veins typically drain into the left brachiocephalic vein
• The right inferior thyroid vein may drain into the right brachiocephalic vein

Surgical Significance

• The middle thyroid vein (no accompanying artery) can be torn if the lobe is mobilised without first ligating it → brisk haemorrhage from the internal jugular vein
• The inferior thyroid veins lie across the front of the trachea — important in low collar incision tracheostomy, where these veins and possibly the thyroidea ima artery lie in the operative field
• Venous engorgement and collateral formation occur in substernal/retrosternal goitre where the inferior thyroid veins are compressed by the goitre in the thoracic inlet