Thyroid hemiagenesis: clinical significance in the patient with thyroid nodule.

Thyroid hemiagenesis is a rare abnormality in which one thyroid lobe fails to develop. Most of the patients diagnosed have an associated thyroid disease. We report the case of a 32-year-old woman who presented with a left thyroid mass which had been gradually increasing in size over a period of two years. A thyroid scan revealed the absence of the right thyroid lobe and isthmus, and a hypoactive nodule was evident in the lower pole of the left lobe. Ultrasonography confirmed the right lobe and the isthmus agenesis. The operative findings confirmed hemiagenesis of the right lobe and nodular hyperplasia in the left lobe. The purpose of this report is to present a patient with hemiagenesis of the thyroid gland who concomitantly had nodular hyperplasia; we also stress the importance of pre-operative differentiation between benign lesions and malignancy in order to aid critical decision making and to facilitate preservation of thyroid function if possible.