A rare variant of thyroid gland vascularization.

Usually the thyroid gland obtains its blood via two paired arteries. One pair, the right and left superior thyroid aa., most commonly arises from the external carotid aa. and the second pair, the right and left inferior thyroid aa. commonly arises from the thyrocervical trunk of the subclavian a. In this particular case the right inferior thyroid a. was replaced by an artery branching off the right internal thoracic a.; the left inferior thyroid a. was replaced by an artery branching off the vertebral a. between the transverse process of the second and third cervical vertebrae. This finding might be explained by the suggestion that in the fetus there exists an anastomotic arterial chain ventral to the spinal column consisting of the thyrocervical trunk and the ascending cervical a. which itself is connected to the vertebral a.