Non-elevation of TSH after total thyroidectomy: a surgical surprise.

A 31-year-old woman with papillary carcinoma of the thyroid with right cervical lymph nodal metastasis underwent total thyroidectomy with modified radical neck dissection. At follow-up 6 weeks after surgery, she had not developed clinical features of hypothyroidism and her thyroid-stimulating hormone (TSH) was within normal limits. Further evaluation including technetium scintigraphy of the thyroid and MRI of the chest confirmed thyroid tissue, thyrothymic thyroid rest (TTR), in the superior mediastinum. The patient's TSH elevated well after reoperation of TTR. She underwent radioiodine ablative therapy and suppressive thyroxine therapy as per the protocol for well-differentiated thyroid cancer follow-up. The clinical importance of these embryological rests of thyroid tissue, especially in the management of thyroid malignancies, is discussed in this report.