What is the cause of this patient's presentation?
Proximal superior mesenteric artery occlusion with ischaemia and small bowel infarction.
What is the underlying cause of small bowel infarction in this patient?
Superior mesenteric artery (near) occlusion due to a recurrent pancreatic mass, complicated by superimposed hypotension or acute thrombosis.
Why is the ascending colon involved but not the distal transverse colon?
The superior mesenteric vein supplies all the small bowel (except for proximal duodenum), caecum, ascending colon and variable parts of the transverse colon (usually most of it). The inferior mesenteric artery supplies the descending colon, with collaterals linking the two territories near the splenic flexure.
There is extensive small bowel dilatation with loops showing absent mural enhancement and mural gas (particularly in the jejunum). The ascending colon appears thick-walled, up to the proximal transverse colon. Gas is also seen in the branches of the superior mesenteric vein, and peripherally in the liver. A small amount of free peritoneal fluid is present.
There is evidence of prior pancreatic surgery with a mass seen in the surgical bed, encasing and occluding the superior mesenteric artery.
Cavernous transformation of the portal vein.