Intrathyroidal metastasis of tonsillar squamous cell carcinoma masquerading as a primary thyroid tumor

Intrathyroidal metastasis of tonsillar squamous cell carcinoma is rare. To date, only six cases have been reported in the literature. This case was unusual and presented with thyromegaly before the diagnosis of the primary tumor. A 55-year-old male patient was suspected to have a primary thyroid tumor with nodal metastasis. The thyroid gland was diffusely enlarged, with no discernible mass. Histologically, the thyroid parenchyma revealed extensive endolymphatic tumor emboli, which were positive for p40 and p16 in a background of chronic lymphocytic thyroiditis. Positron emission tomography-computed tomography revealed hypermetabolic activity in the right tonsillar region. Tonsillar biopsy revealed human papillomavirus-positive squamous cell carcinoma. The present case is the first reported case of intrathyroidal metastasis of tonsillar squamous cell carcinoma with an initial clinical presentation of thyroid enlargement before the primary tumor of tonsillar cancer was diagnosed.