Heterogenous group of disorders, clinico-pathologic process characterized by inflammation within walls of blood vessels,  compromise of vessel lumen, and resulting ischemia
Presentation varies greatly depending on etiology and specific vessels affected
Classification by size of vessels predominantly involved
Large-vessel:
Takayasu arteritis
Giant cell arteritis (temporal arteritis)
Medium-vessel:
Kawasaki disease
Polyarteritis nodosa
Thromboangiitis obliterans (Buerger disease)
Primary angiitis of the central nervous system
Small-vessel:
Henoch-Schönlein purpura
ANCA-associated<unk> es:
Granulomatosis with polyangiitis (Wegner's)
Eosinophilic granulomatosis with polyangiitis (Churg-Strauss)
Microscopic polyangiitis
Cutaneous leukocytoclastic angiitis (“hypersensitivity<unk> ”)
Essential cryoglobulinemia, cryoglobulinemic<unk>  due to hepatitis C
Behcet's disease
Secondary<unk> es and other/miscellaneous
Drug-induced<unk> 
Serum sickness<unk>  associated with other rheumatic diseases (e.g. SLE)
Takayasu arteritis
Giant cell arteritis (temporal arteritis)
Kawasaki disease
Polyarteritis nodosa
Thromboangiitis obliterans (Buerger disease)
Primary angiitis of the central nervous system
Henoch-Schönlein purpura
ANCA-associated<unk> es:
Granulomatosis with polyangiitis (Wegner's)
Eosinophilic granulomatosis with polyangiitis (Churg-Strauss)
Microscopic polyangiitis
Cutaneous leukocytoclastic angiitis (“hypersensitivity<unk> ”)
Essential cryoglobulinemia, cryoglobulinemic<unk>  due to hepatitis C
Behcet's disease
Granulomatosis with polyangiitis (Wegner's)
Eosinophilic granulomatosis with polyangiitis (Churg-Strauss)
Microscopic polyangiitis
Drug-induced<unk> 
Serum sickness<unk>  associated with other rheumatic diseases (e.g. SLE)
Vasculitis syndromes
Abnormal platelet count and/or coagulation
Rickets
Septicemia
Lymphangitis
Idiopathic thrombocytopenic purpura 
Deep venous thrombosis
Hemolytic uremic syndrome