We report the case of a 55-year-old woman with cerebral proliferative angiopathy (CPA). Her medical history included brain surgery for small vascular lesions and suspicion of cerebral malignancy. C methionine PET (C-METH PET) demonstrated a diffusely increased uptake on the right hemisphere. Contrast-enhanced MRI documented a massive lesion with a diffuse "nidus" appearance, involving the right cerebral hemisphere (sparing the inferior frontal gyrus and the anterior frontal lobe), the brainstem, and the middle cerebellar peduncle. Pathology confirmed the diagnosis of CPA and, after radiation treatment, the patient presented with clinical and radiological response.