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 diagnosis was made as a result of evaluation and treatment of a thyroid nodule (4), diffuse thyroid enlargement with thyrotoxicosis (2), and a simple goiter in a patient with a prior history of radiation treatment for facial acne. In five patients thyroid scintigraphy demonstrated unilateral absence of function, four of whom had an ultrasound exam of the neck that revealed a corresponding absence of thyroid tissue. In one patient the diagnosis was made incidentally on a screening ultrasound exam of the neck. Thyroid hemiagenesis was unsuspected preoperatively in one patient with Graves' disease because of marked hyperplasia of a single thyroid lobe and isthmus. Thyroid hemiagenesis was confirmed in four patients who underwent thyroidectomy. The presence of a thyroid isthmus was established in six patients. Postoperatively, all patients were treated with thyroid hormone. Associated thyroid pathology included 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 unilateral absence of function on thyroid scintigraphy and confirmed by ultrasonography. Recognition of this rare congenital anomaly is important to avoid unnecessary contralateral neck exploration with its potential morbidity and to insure that all patients receive careful follow-up and appropriate thyroid hormone therapy when necessary.