Autoimmune? continued
Questions in the Pediatric Endocrinology forum are answered by Dr. Deanna L Aftab Guy, affiliated with Vanderbilt Children's Hospital. Topics covered include adrenal problems, diabetes insipidus, menstrual irregularities, obesity, parathyroid abnormalities, pituitary abnormalities, puberty concerns, rapid growth, rickets and bone disease, short stature, and thyroid.

It does not sound like thyroid, the ultrasound, CT scans would have made mention to the thyroid, but it is good to look at that. This is not an endocrine issue and I would recommend that you work with the pediatric surgeon to consider the need for biopsy which will give the definitive diagnosis. An uptake study will look at thyroid function per se, not necessarily look at cancer versus no cancer. The thought is that if there is a nodule identified in a thyroid and the uptake is low as compared to the rest of the gland there is more concern of a suspicious thyroid nodule. But based on your history you have not even described a thyroid problem rather lymph nodes in the neck.
So the uptake study is a thought but working with your surgeon is more important.