Emphysematous pyelonephritis is acute necrotizing inflammation involving the renal parenchyma, collecting system, or perinephric tissue. It is caused by gas-forming organisms, mostly Escherichia coli (49%), Klebsiella pneumoniae (20%) and Proteus mirabilis  (17 %) ¹. Risk factors are including diabetes mellitus (85%) and urolithiasis (33%) ². The patient might present with urosepsis and CT is highly sensitive in diagnosis. Jeng-Jong Huang and Chin-Chung Tseng organized CT based classification might help in the prognosis of the patient ³. Emphysematous pyelonephritis CT classification includes (1) class 1: gas in the collecting system only; (2) class 2: gas in the renal parenchyma without extension to extra-renal space; (3) class 3A: extension of gas or abscess to perinephric space; class 3B: extension of gas or abscess to para-renal space; and (4) class 4: bilateral or solitary kidney with emphysematous pyelonephritis.

This case was admitted from the emergency department with urosepsis. She presented with the classic pyelonephritis triad including flank pain, fever and rigors. She showed systemic inflammatory response signs including blood pressure 88/51 mmHg, WBCs count 30.3 10⁹/L, CRP 230 mg/L. CT showed obstructed left kidney by ureteric stone as well as gas in the collecting system not involving the renal parenchyma. She had no recent surgical history to account for the presence of gas in the left kidney. Of note, the patient was not diabetic. The CT showed class 1 Huang-Tseng CT classification. The patient was treated non-operatively by intravenous antibiotics and insertion of a left ureteric stent although she needed intensive care admission for 4 days. Eventually, she was stepped down to the ward for 7 days and discharged home after full recovery. The patient will be booked later for ureteroscopic stone removal electively.