Papillary thyroid carcinoma metastasis to a branchial cleft cyst

Branchial cleft cysts (BCCs) are the most common benign masses of the lateral neck. However, rarely, it can develop into a malignant cyst, either as a primary or a metastatic lesion. We report an extremely rare case of papillary thyroid carcinoma (PTC) metastasis to the BCC. The patient clinically presented with a palpable neck mass, and computed tomography revealed a well-defined, thin-walled cystic mass with a small contrast-enhanced mural nodule. Surgical excision of the cystic mass was performed, and the histopathologic results revealed a BCC with a microscopic papillary carcinoma. Thyroid evaluation and thyroidectomy were subsequently performed, and a PTC was confirmed. The imaging findings and differential diagnosis are discussed in this report.