The sections shows skin and subcutaneous adipose tissue with a deep medium-sized artery (approximately 200 micrometers in diameter) that has extensive fibrinoid necrosis of the vessel wall, a lymphocyte predominant infiltrate and luminal thrombosis. Histocytes, focally with hemosiderin, and occasional plasma cells are noted. Other medium-sized vessels and small vessels (less than 100 micrometers in diameter) appear to be involved by the same process; however, they do not show definite fibrinoid necrosis. No granulomas are present. Neutrophils and eosinophils are not a component of the lesion. Stains for microorganisms (PAS, Gram, GMS) are negative. Mild vessel wall-thickening and delicate perivascular fibrous tissue is seen.
Skin, right lower leg, biopsy - non-granulomatous, subacute, medium-vessel vasculitis, consistent with polyarteritis nodosa.