thyroid isthmus

The thyroid isthmus connects together the lower thirds of the lobes; it measures about 1.25 cm.

A fibrous or muscular band is sometimes found attached, above, to the body of the hyoid bone, and below to the thyroid isthmus, or its pyramidal lobe.

The thyroid isthmus is variable in presence and size, can change shape and size, and can encompass a cranially extending pyramid lobe (lobus pyramidalis or processus pyramidalis), remnant of the thyroglossal duct.

It is also anatomically related to the thyroid gland; although the thyroid isthmus is inferior to it, the two lobes of the thyroid extend superiorly on each side of the cricoid as far as the thyroid cartilage above it.