Poorly differentiated thyroid carcinoma (PDTC) shows histological and biological features intermediate between those of differentiated thyroid carcinoma (papillary thyroid carcinoma and follicular thyroid carcinoma) and anaplastic thyroid carcinoma. Skull base metastasis from thyroid carcinoma is rare. Herein, we report the case of a patient with PDTC whose presenting clinical feature was a skull base metastasis. A 69-year-old man who presented with a one-year history of headache was diagnosed as having a left-sided skull base tumor and referred to our hospital. Based on the findings at the initial examination, we suspected a middle ear paraganglioma invading the left clivus, posterior cranial fossa, sigmoid sinus, and jugular foramen. FDG-PET/CT revealed accumulation in the Th10 vertebra and also a small nodule with increased uptake in the right lobe of the thyroid, in addition to increased uptake in the skull base tumor. Biopsy of the skull base tumor was performed via mastoidectomy, and histopathological examination of the specimen revealed metastatic carcinoma from the thyroid with the following immunohistochemical staining profile: CKAE1/AE3+, CK7+, CK20-, PAX-8+, TTF-1+, and p63-. Total thyroidectomy was performed and histopathological examination of the resected specimen revealed the diagnosis of PDTC. Therefore, the patient subsequently also received radioactive iodine treatment. While skull-base metastasis from a thyroid carcinoma is rare, it is important to consider it in the differential diagnosis of a skull base tumor.
