Metastatic Papillary Thyroid Carcinoma in the Lymph Nodes Without Identifiable Primary Tumor in the Thyroid

Papillary thyroid carcinoma (PTC) is the most common thyroid neoplasm. While its initial presentation as metastasis is not uncommon, metastasis to the lymph nodes without a primary tumor is extremely rare. Here we report an unusual case of metastatic PTC within the lymph nodes without an identifiable primary tumor in the thyroid gland. We report a case of a 45-year-old man who presented with neck swelling detected on a routine physical examination. The patient was asymptomatic, and his thyroid function was normal. Ultrasound of the thyroid revealed a well-circumscribed isoechoic 4.5 cm mass in the mid/lower pole of the right lobe. The patient had a congenitally absent left thyroid lobe. CT neck showed no evidence of cervical lymphadenopathy. Fine-needle aspiration was suspicious for a neoplasm, and surgical excision was recommended. The patient then underwent right thyroid lobectomy and isthmusectomy. Gross examination of the thyroid revealed two nodules (4.4 cm and 2 cm) in the right lobe. The entire lobe and isthmus, including the two nodules, were submitted for histologic evaluation, which revealed two encapsulated lesions with microfollicular architecture. The cells displayed hyperchromatic small round cuboidal nuclei with absent nuclear features of PTC. These findings were consistent with follicular adenomas. Interestingly, two of the six central neck lymph nodes were positive for subcapsular metastatic PTC.