Abstract
The metastasis from a primary lung adenocarcinoma to the thyroid is an infrequent occurrence. Typically, malignancies arising from the breast or kidney are more commonly associated with metastatic involvement of the thyroid gland. Here, we report the case of a 63-year-old female with primary lung papillary adenocarcinoma presenting moderate thyroid swelling and progressive shortness of breath. Ultrasound of the neck demonstrated diffusely enlarged and heterogeneously hypoechoic thyroid parenchyma, accompanied by microcalcifications and bilateral enlargement of level III and IV lymph nodes. Fine-needle aspiration cytology of the thyroid gland revealed papillary carcinoma, The Bethesda category VI. Immunocytochemistry positive for TTF1 and Napsin A and negative for PAX 8 proved it to be a primary lung papillary adenocarcinoma metastasizing to the thyroid. Contrast-enhanced computed tomography of the thorax demonstrated gross right pleural effusion with collapse and consolidation of the entire lung parenchyma. This case highlights the importance of cell block and immunocytochemistry in the accurate diagnosis of metastatic thyroid malignancy.