Gastrointestinal Imaging

Polyarteritis nodosa

(PAN), multisystem, necrotizing inflammation of small and medium-sized muscular arteries in which involvement of visceral arteries is characteristic. The lesions are segmental and tend to involve bifurcation and branchings of arteries. They may spread circumferentially and involve adjacent veins. However, involvement of venules is not seen in classic PAN and if present suggests microscopic polyangitis. In the acute stage PAN is characterized by a polymorphonuclear neutrophil infiltrate of all layers of the vessel wall, intimal proliferation and fibrinoid necrosis of the vessel. This results in arterial thrombosis and infarction of the tissues supplied by the involved vessel. Small multiple aneurysmal dilatations are frequently present in the involved arteries.

Clinical symptomatology includes arthralgia, hypertension, abdominal pain, bowel infarction and perforation and hepatic infarction. The liver and the gastrointestinal tract are commonly involved. The diagnosis of PAN is based on the demonstration of the characteristic findings of vasculitis on biopsy material of the involved organs.

The angiographic demonstration (Fig.1) of multiple small aneurysms of the small and medium-sized arteries in the visceral organ involved is, however, considered as highly suggestive for the diagnosis of PAN. In addition angiography may reveal occlusion of small arteries and areas of infarction. The microaneurysms in the liver can also be suggested during the early arterial phase of spiral contrast enhanced CT or on MR angiography. Both techniques can also visualize segmental liver infarction in patients with PAN.

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Fig.1

Polyarteritis nodosa of the liver. Angiography of the hepatic artery demonstrates multiple small aneurysmal dilatations (arrows) of the second and third order branches of the hepatic artery.
Polyarteritis nodosa, Fig.1