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From question on page 1740
The axial computed tomography (CT) image (fig 1) shows peripheral fine branching intrahepatic air, consistent with portal venous gas. This was confirmed (arrow) on the coronal reconstructed CT image (fig 2), along with loops of dilated bowel. The coronal image (fig 3) showed reduced contrast enhancement near the origin of the superior mesenteric artery in keeping with occlusion (arrow).
Mesenteric arterial insufficiency has many causes but the abrupt onset in this case would be suggestive of embolic disease secondary to atrial fibrillation. In cases of mesenteric vascular disease, it is important to differentiate ischaemia from frank luminal infarction because the latter is associated with a dire prognosis. On plain radiographs the presence of portal venous gas is usually pathognomonic of transmural infarction. However, advances in CT technology allow detection of tiny volumes of portal air and thus its presence is no longer considered necessarily premorbid. In fact, the presence of portal air on CT may be caused by non-ischaemic aetiologies in up to 20% of cases. The most reliable signs of transmural infarction in suspected mesenteric ischaemia are free air or fluid. The commonest CT sign in mesenteric ischaemia is bowel wall thickening, although absent in this case.
Early surgical intervention is essential in treating mesenteric ischaemia. However, as this case illustrates, portal venous gas when identified on the latest CT machines is not necessarily immediately premorbid, as this patient survived on conservative treatment for over 72 hours. It is also important to realise that when portal gas is identified on these CT systems, it is not pathognomonic for mesenteric arterial insufficiency and, as is usually the case in medicine, one must treat the patient and not the diagnostic test.