In patients who have undergone total thyroidectomy without hormone replacement, normal serum thyroid-stimulating hormone and thyroglobulin levels are indicative of the presence of an ectopic thyroid remnant, such as a retrosternal thyrothymic rest, rather than complete surgical resection.

After the main thyroid gland is removed, a small piece of thyroid tissue left behind in the chest can still make thyroid hormones and a protein called thyroglobulin. This tissue responds to the body’s signals like a normal thyroid, keeping hormone levels normal without any medication. The body detects these normal hormone levels and stops producing the signal that tells the thyroid to work, so TSH stays low or normal. This means normal hormone levels after surgery don’t always mean all thyroid tissue is gone — it could mean hidden tissue is still working.