Cerebral Parenchymal Photopenia on FDG-PET/CT Reflecting Vasogenic Edema Due to Leptomeningeal Metastasis in Breast Cancer.

A 61-year-old woman with metastatic breast cancer presented with migrainelike episodes over the past 10 months. FDG-PET/CT(PET/CT) showed relatively symmetric areas of photopenia predominantly in the bilateral superior parietal lobules. Subsequent contrast-enhanced MRI revealed leptomeningeal metastasis in the bilateral posterior parietal regions with associated vasogenic edema in the adjacent brain parenchyma. There was no clear evidence of parenchymal metastasis on MRI. After chemotherapy, the areas of abnormality resolved on PET/CT 8 months later, and the patient showed interval symptomatic improvement. The present case demonstrates brain parenchymal photopenia on PET/CT as an indirect sign of leptomeningeal metastasis reflecting regional vasogenic edema.