Thyroid dysgenesis in monozygotic twins: variants identified by scintigraphy.

The unusual occurrence of neonatal hypothyroidism in monozygotic twins is reported. Scintigraphy demonstrated that permanent hypothyroidism in one resulted from an ectopic suprahyoid thyroid, while in the other, the transient hypothyroid state was associated with thyroid hemiagenesis. These findings suggest that the anomalies represent variants of the same developmental aberration.