Fig. 2

IgG4 producing plasma cells in the cerebrospinal fluid and intradural tissue. A Cytologic examination of cerebrospinal fluid (CSF) revealed a marked immunoreactivity of plasma cells stained with an IgG4 antibody. Lymphocytic pleocytosis with IgG4 producing plasma cells (IgG4 immunohistochemistry, 40-fold magnification). B, C Histologic examination of the surgically removed intradural tissue revealed an inflammatory process characterized by an increased number of IgG4 positive plasma cells (\(\approx\) 25% of plasma cells, > 50% IgG4/IgG ratio) (B H&E stain, C IgG4 immunohistochemistry, tenfold magnification, in the insets 40-fold magnification)