Agenesis of the isthmus of the thyroid gland.

The thyroid is an endocrine gland composed of two lobes connected by the isthmus tissue. Thyroid isthmus agenesis is a rare condition, and only a few cases have been reported in the literature. Here, we discuss the case of a 56-year-old female patient in whom agenesis of the thyroid isthmus was discovered incidentally during surgery for a multinodular goitre. When agenesis of the isthmus is found, associated thyroid lobe agenesis and the presence of ectopic thyroid tissue must be considered. In addition, associated autoimmune thyroid nodule, thyroiditis, primary thyroid carcinoma, metastasis, and amyloidosis must be considered in the differential diagnosis. Preoperative awareness of potential agenesis of the isthmus and its associated thyroid anomalies in patients with planned thyroid surgery will significantly contribute to safety during surgical procedures and result in fewer surgery-related complications.