Septic acute kidney injury accounts for close to 50% of all cases of acute kidney injury in the intensive care unit and, in its various forms, affects between 15% and 20% of intensive care unit patients. However, there is little we really know about its pathophysiology. Although hemodynamic factors might play a role in the loss of glomerular filtration rate, they may not act through the induction of renal ischemia. Septic acute renal failure may, at least in patients with a hyperdynamic circulation, represent a unique form of acute renal failure: hyperemic acute renal failure. Measurements of renal blood flow in septic humans are now needed to resolve this pivotal pathophysiological question. Whatever may happen to renal blood flow during septic acute kidney injury in humans, the evidence available suggests that urinalysis fails to provide useful diagnostic or prognostic information in this setting. In addition, nonhemodynamic mechanisms of cell injury are likely to be at work. These mechanisms are likely due to a combination of immunologic, toxic, and inflammatory factors that may affect the microvasculature and the tubular cells. Among these mechanisms, apoptosis may turn out to be important. It is possible that, as evidence accumulates, the paradigms currently used to explain acute renal failure in sepsis will shift from ischemia and vasoconstriction to hyperemia and vasodilation and from acute tubular necrosis to acute tubular apoptosis or simply tubular cell dysfunction or exfoliation. If this were to happen, our therapeutic approaches would also be profoundly altered.

The role of cross-sectional imaging in the diagnosis of Crohn disease has expanded with recent technologic advances in computed tomography (CT) and magnetic resonance (MR) imaging that allow rapid acquisition of high-resolution images of the intestines. To acquire images of diagnostic quality, administration of a fairly large amount of intraluminal contrast agent prior to examination and scanning with intravenous contrast material injection are necessary. Both CT and MR imaging are reported to have a sensitivity of over 95% for the detection of Crohn disease; however, they may not allow early diagnosis. Colonoscopy and conventional enteroclysis studies are indicated for patients with early-stage disease. At more advanced stages, CT and MR imaging can help identify and characterize pathologically altered bowel segments as well as extraluminal lesions (eg, fistulas, abscesses, fibrofatty proliferation, increased vascularity of the vasa recta, mesenteric lymphadenopathy). These modalities can also clearly depict inflammatory lesion activity and conditions that require elective gastrointestinal surgery, thereby aiding in treatment planning. In the clinical setting, CT is currently the imaging modality of choice at most institutions; however, it is expected that MR imaging will soon play a comparable role. CT or MR imaging should be included in a comprehensive evaluation of patients with Crohn disease, along with conventional imaging and clinical and laboratory tests.