How does a thyroid scan diagnose congenital hypothyroidism?

A thyroid scan is a way for a doctor to see the shape of your child's thyroid. The doctor will inject a radioactive isotope into your child's elbow. This isotope then travels through the bloodstream to the thyroid. A camera then takes a photo of the thyroid, which is more visible than usual due to the isotope. Then the doctor can see if the thyroid is malformed due to congenital hypothyroidism.