Fig. 1

Macroscopic, magnetic resonance imaging and histologic imaging of the CNS space-occupying lesions. Panel A: macroscopic appearance of a lesion enucleated during neurosurgical procedure. Panel B: MRI shows multiple intraparenchymal subcortical cystic lesions of varying sizes in the right frontal and left temporal lobes. On T2 weighted images these lesions are characterized by a thin rim of intermediate signal intensity and are surrounded by a small area of perifocal high intensity zone most consistent with vasogenic edema. High central intensity on DWI with corresponding low signal on ADC maps reflects restricted diffusion within the lesion. There is a peripheral ring of enhancement on T1 weighted sequences obtained after gadolinium-based contrast agent injection. Panel C: histologic analysis of the lesion shown in panel A. Figure (A): Haematoxylin–Eosin, 40×: (a) a diffuse inflammatory infiltrate composed of histiocytes and less numerous plasma cells, lymphocytes and granulocytes can be seen in a fibrotic tissue, also with incremented vascularization; (b) Immunohistochemistry CD138, 40×: this staining highlights the plasma-cellular infiltrate; (c) Immunohistochemistry IgG, 40×: shows a high number of IgG-positive cells amidst the inflammatory infiltrate; (d) Immunohistochemistry IgG4, 40×: high number of IgG4-positive cells: in a hot-spot of 470 plasma cells more than 10 IgG4 + per HPF can be seen; IgG4/IgG ratio is also increased (45%)