A lymph node metastasis of papillary thyroid carcinoma as a giant cervical cyst without a primary tumor in the thyroid gland: a case report.

Background: Papillary thyroid carcinoma (PTC) comprises the vast majority of all thyroid cancers. Lymph node metastases may be present even when the primary tumor is small and intrathyroidal. Metastatic lymph nodes of PTC presenting as giant solitary cervical cysts with no evidence of primary tumors in the thyroid gland even by postoperative pathological examination are rare.

Case presentation: A 33-year-old Chinese woman presented to the hospital with an incidental mass in her right neck. Ultrasonography and magnetic resonance imaging revealed a giant right cystic mass in the inferior submandibular gland. The patient underwent mass dissection. Histopathological assessment indicated metastatic papillary carcinoma from the thyroid. Total thyroidectomy and bilateral selective neck dissection were performed. Meticulous pathological examination revealed no lesions in the thyroid. After 18 months of follow-up, no signs of recurrence were noted.

Conclusion: It is difficult and challenging to differentially diagnose between ectopic PTC and lymph node metastasis from PTC. Meticulous pathological evaluation of surgical specimens is key to making a definitive diagnosis.