Major criteria:
(1) Neutrophils and karyorrhectic debris (nuclear dust) in vessel walls.
(2) Necrosis of endothelial cells and vessel walls with fibrin deposition.
Minor criteria:
(1) Endothelial cell swelling.
(2) Hemorrhage in continuity with vessel (extravasated red blood cells).
(3) Thrombosis.
(4) Epidermal necrosis.
(5) Epidermal and subepidermal vesicles.
(6) Mixed infiltrate, including monocytes and eosinophils in an adventitial location.
(7) Perivascular reparative fibroplasia.
(8) Aneurysm formation.
(9) Calcinosis.
Interpretation:
• The histopathologic diagnosis of vasculitis can be made if 1 major AND at least 2 minor criteria are present.
Situations associated with a false negative diagnosis of vasculitis on biopsy:
(1) A biopsy taken more than 24 hours after the appearance of the lesion may miss the changes required to make the diagnosis of vasculitis.
(2) A vasculitis with a segmental involvement may be missed if only a few sections are examined.
(3) A superficial biopsy not including subcutaneous fat may not detect arteritis of small and medium sized arteries.
