Thyroid isthmus agenesis and its clinical significance in a large-scale multidetector CT-based study.

•The incidence of thyroid isthmus agenesis is 4.77%.•Thyroid isthmus agenesis can be classified into clear-cut and tapering-edge types.•The anastomosis of superior and inferior thyroid veins is frequently found in thyroid isthmus agenesis.•Thyroid isthmus agenesis may extend the indication of lobectomy in thyroid cancer.