Giant thyroglossal duct cyst in an adult: CT findings and differential diagnosis.

Thyroglossal duct cysts are the most common congenital cervical anomalies arising from incomplete obliteration of the thyroglossal tract. They are typically diagnosed in childhood and rarely present in adults. Giant TGDCs in adults are exceptionally rare and can mimic thyroid or other midline neck pathologies, posing diagnostic challenge. We report the case of a 37-year-old woman with a 5-year history of a progressively enlarging, elastic, and mobile midline neck mass associated with mild dysphagia. Physical examination revealed a soft, infra-hyoid, midline swelling measuring approximately 6 cm. Thyroid function tests were normal. Contrast-enhanced computed tomography demonstrated a well-circumscribed, homogeneous, non-enhancing cystic lesion consistent with a thyroglossal duct cyst. The patient underwent surgical excision via the Sistrunk procedure. Intraoperatively, a thin-walled cyst adherent to the central hyoid segment was excised en bloc. Histopathological analysis confirmed a benign thyroglossal duct cyst. The postoperative course was uneventful, and no recurrence was observed during 1-year follow-up. This case highlights the diagnostic value of cross-sectional imaging in the evaluation of atypically large midline neck masses and its role in guiding safe and effective surgical planning.