Immunoglobulin G4–related disease (IgG4-RD). A, CT image from a 67-year-old woman who presented with a 3-year history of an enlarging painless mass of the right lacrimal gland fossa, which was identified on CT as a homogeneously enhancing, circumscribed mass diffusely involving the right lacrimal gland (arrow). B–D, Photomicrographs show extensive collagenous fibrosis, lymphoid follicular hyperplasia, and markedly increased plasma cells. E, Immunohistochemistry reveals frequent IgG4 plasma cells, accounting for 40%–50% of total IgG-positive plasma cells. F, A different area of the lymphoid infiltrate stained for IgG4. A subsequent serum test showed an elevated serum IgG4 level. A diagnosis of IgG4-RD was made