Thyroid isthmus
Isthmus glandulae thyroideae
Endocrine & glandsGlandsNeck
- What it is
- The narrow bridge of thyroid tissue joining the two lobes across the front of the windpipe, at the level of the 2nd to 4th tracheal rings.
- Function
- Same follicular tissue as the lobes — makes T4/T3 — and physically links them into one gland.
- Size
- About 1.25 cm tall and wide, 3–6 mm thick
- Clinical note
- In about half of people a pyramidal lobe rises from the isthmus towards the hyoid, a remnant of the thyroglossal duct. Surgeons doing a tracheostomy either divide the isthmus or work just below it.