Unexpected Cortical Uptake on [ 18 F]FP-CIT PET/CT Revealing Delayed Brain Metastases From Renal Cell Carcinoma.

A 77-year-old man with a remote history of renal cell carcinoma (RCC) presented with gait disturbance and underwent delayed [ 18 F]FP-CIT PET/CT to evaluate Parkinsonism. The scan showed focal uptake in the temporoparietal and insular cortices with a focal striatal photopenic defect. Brain MRI confirmed enhancing metastases corresponding to the cortical foci and attributed the striatal abnormality to chronic infarction. Hypervascular metastases such as RCC may exhibit cortical [ 18 F]FP-CIT uptake, possibly from increased perfusion and/or altered blood-brain barrier permeability, reflecting nonspecific tracer retention. Therefore, cortical uptake warrants cautious interpretation and appropriate correlation with clinical history and anatomic imaging for differential diagnosis.