Regrowth of Thyroid Gland: Is This Possible????

Introduction: Adult Thyroid gland which derived from primitive pharynx and neural crest is considered a non-regenerative organ. In this nature, partial or total thyroidectomy is considered a curative treatment for compressive non-malignant goiter. While there is a potential regrowth from stimulating by pituitary thyroid stimulating hormone (TSH), such growth is rarely significant and suppressive TSH therapy is currently indicated only for thyroid malignancy. We present an unusual case of rapid regrowth of normal thyroid tissue that expanded both of the lobes from a single unilateral remnant. Case: 58-year-old male with prior history of multinodular goiter status post subtotal thyroidectomy due to compressive symptoms in 2006 present to our clinic for follow up. Post-operatively, case was complicated with Iatrogenic Hypoparathyroidism thus on replacement of calcium and calcitriol. Follow up neck ultrasound (US), showed no thyroid gland with minimal residual tissue in the right fossa and pathology was benign. In 2011, patient complained of new onset globus sensation, and voice changes which initially concern for gastroenterology issue as the etiology. A neck US unexpectedly revealed normal right thyroid lobe of 5.7 cm without any tissue on the left and no nodule. FNA subsequently performed which was benign tissue. Due to high risk of complication for repeat surgery, annual US was planned for monitoring. In 2013 there was a significant new growth of left thyroid of 1.7 cm in size, no nodules. A repeat US six months later revealed an increase in size in the right from 5.7 to 6.1 cm as well as 1.7 to 2.1cm on the left. Patient denied any compressive symptoms, so we continue with neck US surveillance. By 2020, the right lobe was 6.4 cm and left lobe at 2.4 cm. Within both lobes, now multiple nodules start appearing. FNA were performed on several of those nodules with a benign cytopathology in all of them. Of note, other than regrowth of his thyroid, it is also physiologically functional as patient is euthyroid without levothyroxine replacement since 2013. Discussion: When patient underwent thyroidectomy for benign multinodular goiter, thyroid function test is the only routine test for follow up without additional further images. While it is considered a curative treatment, some regeneration or recurrence is still a possibility which is shown in our case. This is one of the few cases in the literature that we could found about normal thyroid tissue regrowth. It i