Obstruction of the flow in the splanchnic circulation by atherosclerosis; embolism; thrombosis; stenosis; trauma; and compression or intrinsic pressure from adjacent tumors. Rare causes are drugs, intestinal parasites, and vascular immunoinflammatory diseases such as periarteritis nodosa and thromboangiitis obliterans. (From Juergens et al., Peripheral Vascular Diseases, 5th ed, pp295-6)