1. Definition and Key Features Emphysematous pyelitis: Gas is confined only to the pelvicalyceal system, with no renal parenchymal involvement. Most commonly associated with obstructive urinary tract infections (e.g., stones) and gas-producing bacteria such as E. coli. Frequently seen in diabetic patients. 2. Radiological Findings Plain Radiograph Localized radiolucencies: Fine linear or clustered gas densities projected over the kidney, localized to the renal pelvi