A 25 year old man presents to the emergency room with severe abdominal pain. Guaiac test on stool demonstrates occult blood. The patient is taken to exploratory laparotomy, at which a small area of infarcted small bowel is found and surgically removed. Histologic studies on the removed section of bowel demonstrate a recent thrombus occluding a small muscular aery. The adjacent vessel wall shows fibrinoid necrosis with a mixed inflammatory infiltrate containing neutrophils, eosinophils, and mononuclear cells. Which of the following is the most likely cause of the small bowel infarction?

The lesion described is that of polyaeritis nodosa. This condition is often considered to be the prototype for the vasculitides, and characteristically affects small or medium-sized muscular aeries, with a predilection for the gastrointestinal tract and kidney (causing hematuria, albuminuria, or renal failure). Patients are typically young adult males, although both sexes and all ages may have the condition. Characteristically, vascular lesions of different stages may be present. Coicosteroid and cyclophosphamide therapy has improved a formerly poor prognosis. Atherosclerosis can cause bowel infarction, but the histologic description would be that of a plaque. Cystic medial necrosis predisposes for dissecting aoic aneurysm. Monckeberg's aeriosclerosis is a benign condition characterized by ring-like calcifications of vessel walls. Ref: Lin P.H., Kougias P., Bechara C., Cagiannos C., Huynh T.T., Chen C.J. (2010). Chapter 23. Aerial Disease. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.