Solitary Metastasis From Occult Follicular Carcinoma of the Thyroid Mimicking Trigeminal Neurinoma

A 50-year-old woman presented with an extremely uncommon case of solitary metastasis from follicular carcinoma of the thyroid, which presented clinically as trigeminal neurinoma. Neuroimaging detected a tumor in the right petrous apex, which was removed surgically. Histological examination showed metastatic follicular carcinoma of the thyroid. However, no primary tumor was detected by various investigations. The tumor recurred twice, and was treated surgically both times. The patient finally agreed to adjuvant therapy for the suspected primary. Radiotherapy was performed followed by complete thyroidectomy. Examination of the gross specimen found the tumor nodule. Clinically significant metastasis can arise from histologically benign and silent follicular thyroid neoplasms.