Medium size and and small arteries show necrotizing vasculitis, thrombi, fibrin deposits, in later stages fibroblastic proliferation and granulation tissue, finally scarring, obliteration and recanalization. Sometimes aneurysmatic dilatation of the vessels may occurr.

Mixed infiltrate (neutrophils, lymphocytes, histiocytes, some plasmocytes, sometimes eosinophils); hemorrhage. Leukocytoclastic vasculitis of small cutaneous vessels is often present as well. Ischemia of supplied tissues may be present as well.