Necrotizing vasculitis of small- and medium-sized blood vessels
Skin, musculoskeletal, CNS, and GI tract (spares lung)
Predilection to arterial bifurcations and branch sites
Microaneurysm, thrombosis, emboli, organ ischemia, and infarction
Etiology: Idiopathic, HBV, HCV, hairy cell leukemia
Polyarteritis nodosa
Embolism, thrombosis, atherosclerosis
Thromboangiitis obliterans
HIV, Hepatitis, IE, mycotic aneurysm
Takayasu arteritis
Fibromuscular dysplasia
Granulomatosis with polyangiitis
Microscopic polyangiitis, Granulomatosis with polyangiitis 