Huang and Tseng classification of emphysematous pyelonephritis4
| Class | CT appearances |
| I | Gas confined to collecting system |
| II | Gas located in renal parenchyma without extension into extrarenal space |
| IIIa | Gas extending into the perinephric space |
| IIIb | Gas extending into the pararenal space |
| IV | Emphysematous pyelonephritis bilaterally or affecting single-functioning kidney |