Teaching Case

Fever (39°C/102.2°F), chills, confusion, and lethargy in a known diabetic, under treatment with insulin, and with poor glycaemic control.

The patient presented with fever (39°C/102.2°F), chills, confusion, and lethargy. She was a known diabetic, under treatment with insulin, and with poor glycaemic control.
Abdominal ultrasound demonstrated the presence of two highly reflective cortical regions in the right kidney, one in the middle and the other in the lower pole (Fig. 1a). They measured 2.5cm and 3cm in diameter approximately, leaving a shadow with internal echoes ("a dirty shadow") (Fig. 1b). These findings represented pockets of gas inside the renal parenchyma, which was considered a pathognomonic finding for the diagnosis of emphysematous pyelonephritis.
CT confirmed the presence of gas inside the renal parenchyma (Fig. 2a). Furthermore, it revealed radial hypodense areas pre and post IV bolus administration of contrast medium, as well as thickening of the renal fascia and enlargement of the posterior perinephric space, findings suggestive of abscess formation (Fig. 2b).
Intravenous antibiotic treatment was started. Blood and urine cultures grew E. coli. A repeat ultrasound ten days after admission showed complete resolution of the gas pockets, and the development of hypodense areas in their place (Fig. 3).
The patient was symptom-free after four weeks and was discharged from hospital (Fig. 4).

Emphysematous Pyelonephritis (EPN) is a fulminant, life-threatening, necrotizing upper urinary tract infection associated with gas within the kidney and/or perinephric space. The infecting organisms usually consist of mixed flora, including Escherichia coli (68%), Klebsiella pneumoniae (9%), and Proteus mirabilis, as well as Pseudomonas, Enterobacter, Candida and, rarely, Clostridia species. Females are affected twice as often as men. Patients with EPN are typically extremely unwell with circulatory/liver compromise caused by sepsis. There is extensive renal parenchymal gas production and often, renal parenchymal necrosis with extensive perinephric hematoma formation. In most cases, a normal native kidney is involved unilaterally, but in 10% of cases, the condition is bilateral and can arise in a polycystic kidney or in a renal allograft. The gas production from the affected renal parenchyma can become so large that it escapes into the renal vein and then accumulates in the hepatic veins.
Plain abdominal radiography is the initial examination of choice. Plain radiographs are good at depicting air within the renal collecting system but suffer from nonspecificity because of superimposition of gas from the bowel. Moreover, gas in the retroperitoneum and gas within a renal or perinephric abscess may mimic EPN.
Similarly, sonography may fail to recognize the presence of gas due to patient obesity, presence of gas within the intestine or poor patient co-operation. Furthermore, gas within the kidney may mimic renal calculi in addition to producing ultrasound artifact from reverberation echoes and shadowing. CT findings not only are diagnostic of the presence of air within the renal tract but also elegantly depict renal and perirenal anatomy and the spread of infection to the perinephric tissues, even without the infusion of IV contrast medium, which is a major advantage for debilitated patients with poor renal function. However, on CT scans it is not always possible to detect other causes of intrarenal air, such as reflux of air from the bladder, bronchorenal and enterorenal or cutaneorenal fistulae, as may occur with xanthogranulomatous pyelonephritis and focal renal abscesses.
Mortality rate of EPN is 60-75% with antibiotic therapy and 21-29% after antibiotic treatment and nephrectomy. With the increasing availability and use of CT scanning, more powerful antibiotics and better life support, an alternative medical approach to early radical surgery has emerged. We believe that success was achieved by rapid diagnosis and full circulatory support allowing the antibiotics time to work.