Unilateral Thyroid Hypoplasia in a Euthyroid Adult: A Rare Congenital Anomaly

Thyroid hypoplasia is described as a rare congenital anomaly. It is characterized by incomplete development of thyroid tissue, which can be differentiated from thyroid hemiagenesis, where a lobe is completely absent. These cases mostly present asymptomatically and are often found when imaged for unrelated conditions. In this report, we present a case of a 22-year-old euthyroid female who was incidentally discovered to have a hypoplastic left thyroid lobe during ultrasonography. After undergoing further investigations, the thyroid functioning tests were within a normal range (thyroid-stimulating hormone (TSH) 0.751 mIU/L, triiodothyronine (T3) 1.99 pg/mL, thyroxine (T4) 8.21 µg/dL). In addition, an isotope thyroid scan was done, confirming no functioning tissue in the hypoplastic lobe. This case study underlines the significance of differentiating between thyroid hemiagenesis and hypoplasia. In addition, it also highlights the importance of long-term follow-up for assessment of associated thyroid pathologies.