I was diagnosed with Hashimoto's at 19 and had a fairly rigorous thyroid examination at a specialist centre in France at the age of 26 (I was living there at the time). The copy of the letter to my then GP said:
"However, [the ultrasound] showed a thyroid reduced to only its right lobe. The total volume of the thyroid was 7.9 cm3, or half of a normal thyroid. It is generally of hypoechoic echogenicity, as can be seen in these thyroid deficiencies of autoimmune origin."
(Slightly stilted translation all my own work.)
Is it possible that I was actually born with only half a thyroid gland in the first place, if absolutely nothing could be seen of the left lobe? Or could the Hashimoto's have ravaged the left lobe so completely that nothing was left to see? If the former, then frankly it's amazing that I managed to make it to 19 without overt symptoms. If the latter, it would be interesting to see what an ultrasound would show now as the Hashimoto's has gone about its business merrily for another 12 years!