I, too, was only born with one thyroid lobe, the left is completely missing (and yes, it is rare. I've read that only 1/2 of 1% of the population has this condition). The right one is enlarged, with a goiter, but the ENT and Rheumotologist are keeping an eye on it. I've done thyroid imaging and blood tests to ensure it is functioning properly, and there are no "hot" spots on it, and the blood tests indicate that there is no hypo/hyper thyrodism.