A Rare Case of Solitary Brain Metastasis From Papillary Thyroid Carcinoma: The Role of Empiric I-131 Therapy and SPECT/CT (Single Photon Emission Computed Tomography/Computed Tomography) in Achieving an 11-Year Survival

Brain metastases from papillary thyroid carcinoma (PTC) are rare and typically associated with a poor prognosis; however, early detection of solitary lesions can lead to exceptional long-term outcomes. We present the case of a 65-year-old man with a history of multicentric PTC (T1bN0M0, Stage I) treated with total thyroidectomy and postoperative radioiodine ablation 12 years earlier, who presented with rising thyroglobulin (Tg) levels (12 ng/mL) under TSH (thyroid-stimulating hormone) stimulation. Neck ultrasonography and 18F-FDG PET/CT (18-fluorodeoxyglucose positron emission tomography/computed tomography) failed to identify recurrent disease. Empiric high-dose (150 mCi; 5.55 GBq) I-131 therapy was administered. Post-therapy, whole-body imaging demonstrated focal cranial uptake, initially suspected as contamination. I-131 SPECT/CT (single photon emission computed tomography/computed tomography) fusion imaging localized intense iodine uptake to the right occipital lobe. A cranial MRI confirmed a 15 × 15 mm enhancing lesion. The patient underwent craniotomy, and histopathological evaluation confirmed metastatic PTC with follicular features. Immunohistochemistry was positive for TTF-1 and thyroglobulin, with a Ki-67 proliferation index of 20%. The patient remains clinically and biochemically stable and disease-free 11 years after the metastasectomy, demonstrating an exceptionally long survival period for brain metastasis from PTC. This case highlights the diagnostic value of empiric high-dose radioiodine therapy combined with SPECT/CT in detecting occult metastases. Furthermore, the 11-year disease-free survival in our patient underscores that early identification and surgical resection of solitary brain metastases from PTC can lead to an exceptionally favorable long-term prognosis.