Papillary thyroid carcinoma in a branchial cleft cyst

Papillary thyroid carcinoma (PTC) in a branchial cleft cyst (BCC) is exceedingly rare. This case report describes a 53-year-old male with a BCC containing PTC. Despite normal preoperative thyroid imaging, total thyroidectomy revealed multifocal bilateral micropapillary thyroid carcinoma with a contralateral metastatic lymph node, suggesting an aggressive disease course. This finding supports the likelihood that thyroid gland carcinoma metastasized to the BCC. However, the possibility of a primary tumor arising from ectopic thyroid tissue within the cyst cannot be excluded. To our knowledge, this is the 11th reported case of papillary thyroid cancer noted in a BCC. The patient underwent successful treatment, including radioiodine ablation, highlighting the importance of thorough diagnostic evaluation and management in such rare presentations.

While most BCCs are benign, PTC can very rarely present within BCC. Metastatic PTC with a necrotic lymph node is often misdiagnosed as BCC, both radiographically and histologically. Since PTC arising as a primary tumor from ectopic thyroid tissue within a BCC is extremely rare, total thyroidectomy should be considered even in patients with radiographically normal thyroid to rule out micropapillary primary thyroid tumors. A thyroglobulin assay from the needle washout of a fine-needle aspiration of a BCC may help preoperatively identify differentiated thyroid cancers. Micropapillary thyroid cancers (<1 cm) are usually indolent, but some may show nodal metastases and clinical progression.