Thyroid ectopia in a congenital hypothyroid infant.

An infant girl was referred for thyroid screening. The T4 value was 5.0 micrograms/dl (normal 5.0-13.0 micrograms/dl), and the thyroid-stimulating hormone-radioimmunoassay value was greater than 60.0 microIU/ml (normal 0-10.0 microIU/ml). Imaging failed to demonstrate thyroid tissue in the normal anatomic position in the neck. A focal collection of activity was seen, however, on a scan corresponding to the position of the base of the tongue. The finding is consistent with the diagnosis of a lingual (undescended) thyroid.