Figure 16a. Emphysematous pyelonephritis. (a) Type I emphysematous pyelonephritis. Contrast-enhanced CT scan demonstrates gas that radiates diffusely throughout the renal parenchyma (arrow). No associated fluid collections are seen. (b) Type II emphysematous pyelonephritis. CT scan obtained in a different patient shows several small foci of gas, some with associated regions of fluid attenuation (black arrows). These fluid-attenuation regions are thought to represent a more favorable immune response. Vicarious excretion of contrast material is also seen within the gallbladder (white arrow).