Case b - Portal air and necrotic bowel

There is branching air in the liver representing portal venous air. There is dilated, fluid filled large intestine from cecum to splenic flexure. There is probably cecal pneumatosis. There is definitely sigmoid pneumatosis. The wall of the bowel is not thickened.

How do I know this is portal air and not pneumobilia? Look how far into the periphery the air tracks, almost right to the liver edge. I have not seen pneumobilia track this far.  In contrast to the last case, air is not actually seen in the central portal veins.  The air is seen in the anterior, non-dependent portions of the liver.

There are secondary findings that reinforce the diagnosis of portal venous air.  They are present in this case. When bowel becomes necrotic, air forms in the wall of the bowel.  This is called pneumatosis.  This was not present in the previous case but is present here. Later, air tracks into the mesenteric veins and then into the portal vein. If you think you see portal venous air, look for mesenteric venous air and pneumatosis. These findings will clinch the diagnosis.  Mesenteric air is best viewed using lung windows.

In this case there is air in multiple mesenteric veins (here and here). There is even an air-blood level in the SMV! Lastly there are multiple areas of pneumatosis.

The areas of pneumatosis in the sigmoid are very convincing. The air looks like it is situated within the wall of the bowel. The findings in the cecum are suggestive of pneumatosis, but I have been fooled by this appearance before. Notice how the air suggestive of pneumatosis in the cecum is seen dependently between the bowel contents and bowel wall. You cannot definitely see any mucosa between the stool/fluid and the air. Sometimes air can get caught between the bowel contents and the bowel wall and it looks like pneumatosis. I usually give a differential diagnosis in this situation: air caught between stool and the bowel wall (harmless), pneumatosis (harmless or harbinger of doom), or air under some sloughed mucosa as in pseudomembranous colitis (bad but easily treatable). To be absolutely convinced of pneumatosis I like to see the air within the bowel wall and I like to see it in regions where there is no stool. However, in this case, with the obvious portal and mesenteric venous air, I have no problem calling the cecal findings pneumatosis.

On exploration the colon was necrotic and gangrenous to about the splenic flexure.  The sigmoid colon was viable.  Look how thin the wall of the cecum and transverse colon are.  This was dead bowel.  I had always though that ischemic bowel had to be thickened.  That is not the case.  Ischemic and necrotic bowel can have normal thickenss.  Scary . .