Subisthmic accessory thyroid gland in man: a case report and a review of thyroid anomalies.

Morphological variations of the thyroid gland are common and generally occur superior to the gland, reflecting its developmental origin. In this report we describe an accessory lobe located inferior to both lateral lobes and the isthmus. The accessory lobe was supplied by a branch of the right inferior thyroid artery and its vein drained via the plexus thyroideus impar. A discussion of thyroid anomalies is presented and a system for classifying variations of thyroid anatomy is proposed.