Emphysematous pyelonephritis is a serious condition that warrants urgent treatment so early detection and correct diagnosis are important. One differential diagnosis that must be considered is emphysematous pyelitis - a more benign disease where gas production is limited to the excretory system. In emphysematous pyelonephritis (as in this case) gas is seen within and/or around the kidney. 

For the educational purposes, it is worth to compare the x-ray and CT scouts with coronal MPR before treatment to familiarise oneself with the characteristics of the gas pattern.

In addition, gas in the right ureter and bladder detected on CT was not seen on x-ray performed the day before. Probably gas was introduced during instrumentation - the placement of a double J-stent.

Treatment in emphysematous pyelonephritis includes intravenous antibiotics and percutaneous drainage (as in this case).