Editor: Mahmut Akgul (

2022-28/July 18

Contributors: Christine E. Wamsley, Arianna Morton, Li Li

A man in his 60s with a history of diabetes and benign prostatic hyperplasia presented with 6 weeks of fatigue and 3 days of suprapubic tenderness. Ultrasound demonstrated moderate hydronephrosis of the right kidney and urinary retention. He returned 1 week later with lethargy, hyperglycemia (blood glucose 850), and continued dysuria. Urine and blood culture were positive for Escherichia coli. On imaging, extensive gas was noted in and around the kidneys bilaterally. The patient developed septic shock, and bilateral radical nephrectomy was performed. CLICK ON THE BELOW THUMBNAILS TO ENLARGE PHOTOS.


a) Nephrolithiasis

b) Xanthogranulomatous pyelonephritis

c) Emphysematous pyelonephritis

d) Acute prostatitis

e) Acute cystitis

1.  c

Emphysematous pyelonephritis

On gross examination, the renal parenchyma of both kidneys was tan-brown, red, congested with hemorrhage and necrosis comprising 50% of the cut surface of the right kidney and 30% of the left kidney. An air space was also identified in the perinephric space in a representative area (Figure 1). Microscopic examination demonstrated multifocal hemorrhage, acute pyelonephritis with macro- and microabscess formation and foci of micro- and macro-infarction of the kidney parenchyma involving the renal pelvicalyceal system, extending to the kidney cortex and peri-renal fat in both kidneys. The abscesses were filled with abundant neutrophil infiltration, necrotic kidney tissue and bacterial colonies (Figure 2). Additionally, numerous gas-filled cysts had formed within the abscesses and adjacent necrotic kidney tissue. A large artery also shows subendothelial neutrophil and mononuclear cell infiltrate consistent with vasculitis. A diagnosis of bilateral emphysematous pyelonephritis was made.

The affected kidney cortex parenchyma exhibited features of diabetic nephropathy, Renal Pathology Society (RPS) class IIb, showing diffuse thickening of the glomerular and tubular basement membranes, and severe mesangial expansion without hypercellularity and nodular formation (Figure 3). There was mild to moderate intimal fibrosis of the arteries and thickening of the arteriolar walls (Figure 4).

Emphysematous pyelonephritis (EPN) is a severe necrotizing infection of the kidney with accumulation of gas in the renal parenchyma, collecting system, and/or perirenal tissue. Up to 95% of cases occur in patients with uncontrolled diabetes mellitus, as was the case with this patient. He had a known history of diabetes (fasting blood glucose of 184 in 2016) that was not being medically managed, and at the time of admission, his hemoglobin A1c was 13.6%. It is hypothesized that high levels of glucose may impair blood supply, which, in combination with reduced host immunity, may facilitate bacterial colonization and gas production. Although the presence of diabetes is a common risk factor for EPN, this condition is not associated with an increased risk of mortality.

There is a greater incidence of EPN in women, which is most likely attributed to an increased susceptibility to urinary tract infections. Escherichia coli remains the most common causative pathogen, though cases related to Proteus mirabilis, Klebsiella pneumoniae, Group D Streptococcus, and coagulase-negative Staphylococcus infection have also been reported. These gas-forming microorganisms ferment glucose and lactose, leading to high levels of carbon dioxide and hydrogen, as well as nitrogen, oxygen, and traces of ammonia, methane, and carbon dioxide, at the site of inflammation. This gas may spread beyond the site of inflammation, with extension to the perirenal space, as seen with this patient; in some cases, gas has been noted all the way into the scrotal sac and spermatic cord. The offending organism is isolated from urine or pus cultures in nearly 70% of the reported cases. Both urine and blood cultures were positive for Escherichia coli in this case. The risk of developing EPN secondary to a urinary tract obstruction is 25-40%. Bilateral EPN, as in this patient, has been reported in 0%-38.5% of cases.

Computed tomography imaging is the gold standard for diagnosis, confirming the presence of gas. Huang and Tseng published a classification system in 2000 based on CT findings. They define EPN as follows: Class 1: gas in the collection system only, Class 2: gas in the renal parenchyma without extension to the extrarenal space, Class 3A: extension of gas or abscess into the perinephric space, Class 3B: extension of gas or abscess into the pararenal space, Class 4: bilateral EPN or solitary kidney with EPN.

Once diagnosed, patients with emphysematous pyelonephritis must be aggressively and immediately treated due to potential life-threatening associated septic complications. Options include medical management with antibiotics alone, medical management with percutaneous drainage, or medical management with emergency nephrectomy. Emergency nephrectomy may be required as a salvage procedure or can be performed immediately if warranted, such as in patients with several risk factors, severe clinical deterioration, or a poor prognosis.

With advancements in imaging and improvements in early surgical intervention, the mortality rate of EPN has declined from 78% in the late 1970s to 21% as of 2018. Mortality primarily arises from septic complications. Studies have shown that blood glucose level, age, sex, and site of infection are not prognostic indicators. Bilateral EPN, thrombocytopenia, acute renal impairment, altered consciousness, and shock, however, are associated with high rates of mortality.

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Christine E. Wamsley, Arianna Morton, Li Li
Thomas Jefferson University School of Medicine
Philadelphia, PA


Kidney, diabetes, emphysematous pyelonephritis.