Well, cysts were indeed found, and a dx of multi-nodular goiter was confirmed. After two different case conferences between specialists and radiologists (and a wait period of almost three weeks that made me a crazy woman wondering if we had a biopsy in the near future) the doctors decided to try Dallas on medication. He's now taking 50 mcg. of Synthroid daily, to see of it will help shrink the enlarged thyroid and reduce the cysts. Hoping and praying that this works for him. The side benefit may be that it helps with his mood and body temperature dysregulation issues.
So far, so good, and no side effects that we can tell. He will be go back in in 8 weeks for another ultrasound and another thyroid blood panel to see if he's made any progress with the medication.
Off topic, but Dallas also earned his 2nd stripe in karate last week, and got all 100s on his math and 2 language tests, making great progress in OT and PT, and his behavior has been manageable. :-)