Papillary Carcinoma of Thyroid Arising in a Thyroglossal Duct Cyst

Abstract

Introduction: Thyroglossal duct cyst (TGDC) is the most common congenital midline neck anomaly. Malignant transformation is rare, occurring in approximately 1% of TGDCs, with papillary thyroid carcinoma (PTC) being the predominant malignancy. Preoperative diagnosis is challenging because malignant TGDC may clinically and radiologically mimic a benign cyst. Materials and methods: A rare case of PTC arising within a TGDC was evaluated using clinical, radiological, gross, histopathological, and immunohistochemical findings. The relevant literature was reviewed to assess the diagnostic and therapeutic significance of this entity. Case report: A 33-year-old woman presented with a painless, gradually enlarging midline suprahyoid neck swelling for four years. Ultrasonography demonstrated a well-defined cystic lesion containing solid nodules and multiple calcifications, with cervical lymphadenopathy. Contrast-enhanced CT suggested a TGDC with possible papillary carcinoma arising within it. Excision of the cyst was performed. Histopathological examination showed a cyst lined by flattened epithelium with focal thyroid tissue displaying papillary architecture, nuclear clearing, and psammoma bodies, diagnostic of PTC. Immunohistochemistry showed TTF-1 positivity, while BRAF V600 was negative. The findings supported PTC arising within a TGDC. Conclusion: PTC arising in a TGDC is a rare entity that may remain clinically unsuspected. Careful histopathological examination is essential for diagnosis, while clinical, radiological and immunohistochemical correlation aids in establishing the diagnosis and guiding appropriate management. Keywords: Thyroglossal duct cyst; Papillary thyroid carcinoma; Ectopic thyroid tissue; Psammoma bodies; TTF-1; Neck swelling.