Comparative Analysis of Metastatic Thyroid Carcinoma versus Ectopic Thyroid Carcinoma in Lateral Neck Masses without Identifiable Primary Thyroid Carcinoma.

Thyroid carcinoma, presenting as a lateral neck mass without an identifiable primary tumor within the thyroid, poses a diagnostic challenge. This comparative analysis aimed to explore the differences between metastatic thyroid carcinoma and ectopic thyroid carcinoma, as both present with a lateral neck mass without evidence of primary thyroid carcinoma. Searches were conducted for studies on thyroid carcinoma in the lateral neck without evidence of primary thyroid carcinoma. A total of 39 patients were identified from 32 reported studies. Metastatic and ectopic thyroid carcinomas were found in 11 and 28 patients, respectively. Metastatic thyroid carcinoma is characterized by evidence of spontaneous primary tumor regression within the thyroid and commonly associated with multiple lymph node metastases in central and lateral neck compartments. Ectopic thyroid carcinoma is more commonly diagnosed in younger patients and is frequently identified in branchial cleft cysts. The coexistence of normal thyroid tissue adjacent to the ectopic thyroid carcinoma was confirmed, and patients with ectopic thyroid carcinoma exhibited significantly higher rates of second-stage thyroidectomy or neck dissection. When complete surgical excision was considered adequate, excision alone was chosen for patients with ectopic thyroid carcinoma. Identifying these differences is valuable for the differential diagnosis and development of treatment strategies for metastatic and ectopic thyroid carcinomas in lateral neck masses without evidence of primary thyroid tumor.