NeuroImages: IgG4-related disease with meningeal and parenchymal involvement on MRI and histopathology.

IgG4-related disease (IgG4-RD) rarely involves the CNS parenchyma. We report a 44-year-old man with left facial numbness and seizures. MRI showed right frontal-parietal dural thickening and parenchymal edema. Biopsy revealed IgG4 + plasma cells (> 50/HPF) with obliterative phlebitis, confirming IgG4-RD. This case highlights the need to consider IgG4-RD in meningo-parenchymal lesions mimicking tumors or infections. Glucocorticoids should be initiated promptly after histopathologic confirmation.