Fig. 1. Findings of chest CT, brain MRI and pathology of the patient with IgG4-related disease. A: Chest computed tomography image shows a bilateral multifocal honeycomb appearance and focal ground-glass opacities. B-D: Brain magnetic resonance imaging. B: Image obtained 5 months prior to the current presentation shows no definite abnormality. C: Axial T1-weighted enhanced image shows focal thickening and dural enhancement. D: Follow-up image after treatment shows that the previously thickened and enhanced lesion has improved. E-H: Pathological features of the surgically resected lung tissue. Obliterating venular vessels (E, arrows) and storiform fibrosis (F, arrows) are observed (hematoxylin and eosin, ×200). Comparison of an IgG-stained field (G; immunohistochemistry, ×400) and an IgG4-stained field (H; immunohistochemistry, ×400). The ratio of IgG4- to IgG-positive plasma cells exceeds 0.4. There are >20 IgG4-stained plasma cells in each high-power field (G).