Nonocclusive mesenteric ischemia is the most likely cause of this patient's jejunal wall thickening and dilation, ongoing hypotension, fever, and abdominal pain. Nonocclusive mesenteric ischemia is caused by decreased mesenteric perfusion in low-flow states such as heart failure, sepsis, profound hypotension, or hypovolemia. It may also occur with use of vasoactive medications such as vasopressors, ergots, triptans, cocaine, and digitalis. This patient most likely developed sepsis following induction chemotherapy. The severe and sustained hypotension from sepsis in addition to the use of vasopressor medications results in decreased mesenteric perfusion.

Although this patient has thrombocytopenia, which can predispose to bowel-wall hemorrhage and CT scan findings of wall thickening, bowel-wall hemorrhage would not be associated with the clinical picture of sepsis and fever.

Ischemic colitis is the most common form of ischemic injury to the gastrointestinal tract. Although the vast majority of cases occur in patients older than 60 years of age, it can be seen in this setting owing to altered arterial flow secondary to hypotension and vasopressor medications. This patient has predisposing factors for ischemic colitis with systemic alterations in blood flow, and the typical clinical features of the disease with left lower abdominal pain and diarrhea. However, the lack of rectal bleeding and absence of left colon inflammatory changes on CT do not support ischemic colitis as the cause for this patient's life-threatening clinical scenario.

Mesenteric artery emboli account for 50% of cases of acute mesenteric ischemia. They are usually of cardiac origin owing to atrial fibrillation or left ventricle thrombus. This patient has no evidence of atrial fibrillation, and the clinical picture of severe, unresponsive hypotension before the onset of the gastrointestinal symptoms makes nonocclusive mesenteric ischemia a more likely diagnosis than mesenteric artery embolism.