Papillary Thyroid Microcarcinoma Revealed by Contralateral Cystic Metastasis Mimicking a Branchial Cleft Cyst.

Abstract

Introduction: Papillary thyroid microcarcinomas (PTMC) can exhibit invasive behavior with lymph node metastasis despite their small size. In some cases, they may present as cystic lymph node metastases, clinically and radiologically mimicking benign lesions such as branchial cleft cysts. These misleading presentations may delay the diagnosis of an underlying thyroid malignancy. We report a rare and atypical presentation of PTMC as a large contralateral cystic lymph node metastasis initially diagnosed as a branchial cleft cyst, highlighting the need to consider metastatic thyroid carcinoma in the differential diagnosis of lateral neck cysts.

Observation: A 51-year-old woman presented with a left lateral cervical mass diagnosed as a second branchial cleft cyst. Surgical excision and histology revealed a metastatic lymph node from papillary thyroid carcinoma. Subsequent workup identified a 4 mm PTMC in the right thyroid lobe. The patient underwent total thyroidectomy, lymph node dissection, and radioactive iodine therapy.

Conclusion: PTMC may behave aggressively and present with misleading cystic nodal metastases. Clinicians should include metastatic papillary thyroid carcinoma in the differential diagnosis of isolated cystic neck masses, even in the absence of an identifiable thyroid lesion on initial imaging.