Acute occlusion of the superior mesenteric artery is followed by infarction of the small intestine and ascending colon. The extent of such infarction depends on the localization and size of the (primary or secondary) thrombosis. As the Table shows, the most frequent primary cause is embolism in some authors' experience and thrombosis in others'.
In animals, complete interruption of the mesenteric circulation leads to irreversible changes after a period ranging from four hours (Nelson et al, Lillehei et al) to seven hours (Glotzer et al). In man, where some residual blood flow may persist, the intestine is capable of recovery after periods of up to 24 hours following the onset of the crisis, provided the circulation be restored to normal (Shaw et al, Klass, Kleitsch, Miller et al, Saris et al). In animal experiments, Glotzer and co-workers confirmed that the intestinal wall exhibits an astounding power of resistance to ischemia.