Hemiagenesis of thyroid gland -a rare presentation

Thyroid dysgenesis (TD) due to embryonic defect in the development of thyroid represents a major cause of congenital hypothyroidism. Hemiagenesis of a thyroid lobe is a developmental anomaly in which one thyroid lobe fails to develop. It can be either due to complete absence or abnormal descent of one lobe. Several genetic mechanisms or environmental factors are proposed for defective lobulation or defective descent but conclusive evidence is yet to be postulated. We report a case of a 21 year old woman who presented with a gradually progressive neck swelling for 3 years. An ultrasound of the neck revealed absent left thyroid lobe with nodule right lobe and Technetium 99m Scintigraphy confirmed it. Thyroidectomy was performed with removal of right lobe and histopathology revealed adenomatous goitre with degenerative changes. This case is reported for its rarity and the importance of hemiagenesis in congenital hypothyroidism