Histopathologic clues to the etiopathogenesis of orbital inflammatory disease: Idiopathic, IgG4-related, neoplastic, autoimmune and beyond

Orbital inflammatory diseases represent a heterogenous group of idiopathic, autoimmune-related, and sometimes neoplastic conditions with overlapping clinical and histopathologic features, as well as variable levels of IgG4-positive plasma cells detected within tissue biopsies. Some histopathologic features, especially in an appropriate clinical context, may point to a specific diagnosis in a given patient. Diagnoses of non-specific orbital inflammation, orbital inflammation related to autoimmune diseases such as granulomatosis with polyangiitis and IgG4-related disease, lymphoma, and xanthogranulomatous diseases are discussed, contrasted and illustrated.