CONGENITAL THYROID HEMIAGENESIS

Failure of embryologic development of a lobe of the thyroid gland is a rare anomaly. In order to characterize this unusual entity, we report our experience in seven patients with thyroid hemiagenesis involving the left lobe in five and the right lobe in two patients. The diagnosi s was made as a result of evaluation and treatment of a thyroid nodule (4), diffuse thyroid enlargement with thyrotoxicosis (2), and a simpl e goiter in a patient with a prior history of radiation treatment for facial acne. In five patients thyroid scintigraphy demonstrated unilat eral absence of function, four of whom had an ultrasound exam of the n eck that revealed a corresponding absence of thyroid tissue. In one pa tient the diagnosis was made incidentally on a screening ultrasound ex am of the neck. Thyroid hemiagenesis was unsuspected preoperatively in one patient with Graves' disease because of marked hyperplasia of a s ingle thyroid lobe and isthmus. Thyroid hemiagenesis was confirmed in four patients who underwent thyroidectomy. The presence of a thyroid i sthmus was established in six patients. Postoperatively, all patients were treated with thyroid hormone. Associated thyroid pathology includ ed adenoma (1), follicular carcinoma (1), colloid nodule (2), Graves' disease (2), and a simple goiter (1). In conclusion, the diagnosis of thyroid hemiagenesis should be considered in any patient with unilater al absence of function on thyroid scintigraphy and confirmed by ultras onography. Recognition of this rare congenital anomaly is important to avoid unnecessary contralateral neck exploration with its potential m orbidity and to insure that all patients receive careful follow-up and appropriate thyroid hormone therapy when necessary.