Imaging in small and medium vessel vasculitis

Vasculitis includes a group of disorders characterized by inflammation of the vessel wall and classified based on the diameter of the predominantly involved vessels. Granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis and Henoch-Schonlein purpura are the important entities in the small vessel vasculitis group, while polyarteritis nodosa and Kawasaki disease represent the medium vessel vasculitis group. The clinical manifestations may be non-specific and there may be considerable overlap with the other disorders. Imaging plays an important role in diagnosis as well as the management of patients with small and medium vessel vasculitis. Imaging allows direct evaluation of the arteries in medium vessel vasculitis. However, the involved vessels in small vessel vasculitis are smaller than the resolution of the current imaging techniques. Hence, only the end organ changes secondary to involvement of small vessels are examined. In this review we discuss the role of current imaging modalities (predominantly computed tomography and magnetic resonance imaging) as well as individual disease entities in the groups of small and medium vessel vasculitis.