Histopathology of vasculitis: Classification, controversies, and concepts

Vasculitis comprises a diverse group of disorders with varying clinical, histopathological, and immunofluorescence findings arising due to an array of underlying pathogenic mechanisms. These varying reactions are primarily a reflection of complex interplay of different cells, vessels, and stroma. There are several controversies and differences of opinions in the diagnostic criteria, classifications, and terminologies. This article deals with different concepts and controversies in the subject, and also attempts to provide an algorithmic approach for the histopathological diagnosis.