Submandibular lymph node metastasis of occult thyroid carcinoma first suspected to be a salivary gland tumor: a case report

BACKGROUND: When diagnosing and treating neck masses, various diseases need to be considered, including benign or malignant tumors, lymph node-related diseases, and cysts. Thus, there may be cases in which making a definitive diagnosis is difficult on the basis of blood testing and imaging alone. CASE PRESENTATION: The patient was an 80-year-old Japanese female who presented with swelling in the right submandibular area. Magnetic resonance imaging and ultrasonography revealed a solid tumor with inhomogeneous content continuous with the submandibular gland. Therefore, the clinical diagnosis was salivary gland tumor. Surgical treatment was performed, and intraoperative frozen-section examination demonstrated submandibular lymph node metastasis of thyroid carcinoma. After surgical treatment, blood test for thyroid gland function yielded normal results except for increased thyroglobulin levels. Further positron-emission tomography–computed tomography and ultrasonography were performed, in addition to fine-needle aspiration biopsy of the thyroid gland and other tests; however, no other thyroid abnormalities were observed. Fine-needle aspiration biopsy revealed no carcinomatous components. Close observational follow-up has been continued without thyroid gland treatment, and as of approximately 8 years postoperation, no recurrence, metastases, or thyroid carcinoma have developed. CONCLUSION: The mass was lymph node metastasis of occult thyroid carcinoma. In general, occult thyroid carcinoma metastasizes to level II–V. To the best of our knowledge, this is the first report of submandibular lymph node metastasis alone of occult thyroid carcinoma.