The Silent Passenger: Incidental Papillary Thyroid Carcinoma in Thyroglossal Duct Cyst

Background: The thyroglossal duct cyst (TGDC) is the commonest embryological thyroid developmental abnormality. It is usual to find dispersed ectopic thyroid tissue within TGDCs, but malignant transformation is expected to occur in less than 1% of cases. We present this unusual case which was misdiagnosed on fine needle aspiration cytology (FNAC) as colloid goitre. Case Report: A 60 year old female presented with swelling in front of neck. At ultrasound examination a diagnosis of benign lesion was rendered as TIRADS 0 in left lobe, TIRADS I in right lobe and TIRADS III in the isthmus. Thyroid hormone assay was within normal limits. At FNAC a diagnosis of Colloid Goitre (TBSRTC) was made. Computed tomography of neck was also suggestive of a benign solid cystic lesion. Left hemi thyroidectomy was done and specimen sent for histopathology which was reported as papillary carcinoma-classic type arising in a thyroglossal duct cyst. Conclusion: The present case highlights the importance of considering malignancy, however infrequent, in the differential diagnosis of TGDC masses, even in the absence of overt suspicious features. The case underscores the need for thorough pathological examination of excised TGDCs to identify such unexpected findings.