Synchronous Medullary and Papillary Thyroid Carcinoma with Mixed-Component Lateral Cervical Lymph Node Metastases: A Case Report

Abstract

Background: Synchronous medullary thyroid carcinoma (MTC) and papillary thyroid carcinoma (PTC) are uncommon thyroid malignancies, whereas mixed-component cervical lymph node metastases containing both tumor components within the same metastatic deposit are exceptionally rare. This case highlights the diagnostic value of integrating discordant site-specific fine-needle aspiration (FNA) findings with serum biomarkers for preoperative recognition of this unusual presentation.

Case Description: A 65-year-old man presented with a progressively enlarging right-sided neck mass accompanied by ipsilateral cervical lymphadenopathy for more than two months. Ultrasonography demonstrated a 4.28 × 2.28 × 2.54 cm Thyroid Imaging Reporting and Data System (TI-RADS) 5 thyroid nodule with multiple enlarged right cervical lymph nodes. Serum calcitonin (Ctn) (1,796.38 ng/L), carcinoembryonic antigen (CEA) (81.69 μg/L), and thyroglobulin (Tg) (163.65 μg/L) levels were markedly elevated. FNA of the thyroid nodule supported MTC, whereas FNA of a metastatic cervical lymph node demonstrated PTC, providing discordant cytological evidence that raised preoperative suspicion of synchronous thyroid malignancies. Total thyroidectomy with bilateral neck dissection revealed multifocal MTC and microscopic contralateral PTC with mixed-component metastases involving 10 cervical lymph nodes. No postoperative complications such as recurrent laryngeal nerve injury or permanent hypoparathyroidism occurred. Serum parathyroid hormone (PTH) levels recovered to 40.85 ng/L at 12 months. Serum Ctn, CEA, and Tg levels remained persistently low (57.29 ng/L, 3.96 μg/L, and 0.39 μg/L, respectively), and follow-up neck CT scans over the 12 months showed no signs of lymphadenopathy.

Conclusions: This case demonstrates that discordant FNA results between primary thyroid lesions and metastatic lymph nodes, accompanied by dual-marker elevation (Ctn, CEA and Tg), strongly indicate synchronous MTC and PTC. A comprehensive radical surgical approach and rigorous dual-biomarker longitudinal surveillance are key to achieving optimal oncological control and preventing diagnostic omissions.