Abstract 23: A rare case of ectopic hyperfunctioning thyroid tissue in thymus gland in an adult woman

Background: Ectopic thyroid tissue is a rare developmental abnormality due to aberrant embryogenesis of the thyroid gland during its passage from the floor of the primitive foregut to its final pre-tracheal position. Intrathoracic ectopic thyroid is a rare occurence of ectopic thyroid, accounting for about 1% of all mediastinaltumours. They are usually euthyroid and present with pressure symptoms. Case History: A 40-year-old lady presented with swelling in neck and thyrotoxic features. Biochemistry showed suppressed thyrotropin level with raised triiodothyronine and thyroxine levels. Ultrasound neck showed bulky left lobe with a well-defined isoechoic nodule with a few cystic areas in the lower pole. Technetium scan revealed avid uptake in thymus with suppressed uptake in right lobe of thyroid and non-uniform uptake in left lobe with a cold nodule in left inferior pole of thyroid gland. FNAC of cold nodule showed benign hyperplastic nodule of Bethesda category 2. She was started on methimazole and became euthyroid over following six months. She is under follow-up. Video assisted thoracoscopic biopsy of ectopic thyroid tissue is planned. Conclusion: Ectopic thyroid tissue is rare and a hyperfunctioningmediastinal thyroid tissue is an even rarer phenomenon. It is important to identify ectopic tissue. Thyroid Scintigraphy plays an important role in diagnosis as highlighted in our case. Follow up for any malignant transformation and management thereof needs special attention requiring multi-disciplinary team approach.