Isthmus
The narrow band of thyroid tissue connecting the two lobes across the front of the windpipe.
The isthmus is the thin strip of thyroid tissue that bridges the right and left lobes at the midline of the neck, crossing the front of the trachea at roughly the level of the second and third rings of cartilage.
It is typically only a centimetre or two wide and a few millimetres thick. Like the rest of the thyroid, it contains hormone-producing follicle cells.
In some people, a nodule or small thyroid cancer is located specifically in the isthmus. When this is the case, a surgeon may perform an isthmusectomy - removal of just this central bridge - rather than an entire lobe.
The pyramidal lobe, when present, extends upward from the isthmus as a thin finger of thyroid tissue.
Related terms
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