Which infection associated with renal ischemia commonly affects diabetics and is characterized by gas formation?

Emphysematous pyelonephritis is the correct answer because it is a severe and potentially life-threatening infection of the kidney that is particularly associated with renal ischemia and commonly affects individuals with diabetes. This condition is characterized by the presence of gas within the renal parenchyma and surrounding tissues, which is a result of gas-producing bacteria that thrive in the necrotic tissue of the kidney. The gas formation can lead to dramatic findings on imaging, including the characteristic appearance of gas bubbles in the renal tissue on ultrasound or computed tomography.

In diabetic patients, the risk for emphysematous pyelonephritis increases due to factors such as reduced immune response, vasculopathy, and the likelihood of renal ischemia, which can compromise normal kidney function and increase susceptibility to infections. The gas production in this type of pyelonephritis is caused by the fermentation of glucose by aerobic or facultatively anaerobic bacteria, commonly E. coli.

The other conditions listed do not typically involve gas formation or the same degree of association with renal ischemia in diabetics. Acute pyelonephritis is an inflammation of the kidney due to a bacterial infection but generally does not involve gas formation. Xanthogranulomatous