Teaching Case

A 68-year-old female patient with polycystic kidney disease presented with high fever, macroscopic haematuria and pain in the right flank. Laboratory studies revealed renal impairment (2.87 mg/dl serum creatinine) and markedly increased C-reactive protein (284 mg/l). Blood and urine culture showed growth of E. coli.

A multi-slice unenhanced CT-scan of the abdomen was made which demonstrated bilateral polycystic kidney disease and a great amount of gas within the bladder lumen (Fig. 1) and in the right kidney (Fig. 2, 3 and 4). The majority of this intrarenal gas in the right kidney was distributed along the pyelocalyceal system. A minority of the gas was located intraparenchymal, most prominent in the wall of some renal cysts. There were no perirenal fluid collections. A small focus of air was also seen within the wall of the gallbladder. Given the gas formation in the bladder wall and the presence of renal gas in the right kidney, the diagnosis of emphysematous cystitis and pyelonephritis was made. Despite aggressive treatment with broad spectrum antibiotics and fluid resuscitation, the patient died one day after admission in our hospital of cardiac arrest.

Emphysematous pyelonephritis is an uncommon acute necrotizing infection of the renal parenchyma and its surrounding tissues. Due to septic complications, it’s a life-threatening condition with a mortality rate of approximately 20%. Up to 95% of the patients have underlying diabetes mellitus. Other identified risk factors are immunosuppression and polycystic kidney disease. Our patient didn’t have diabetes mellitus, but known polycystic kidneys. There is a female predilection (6:1) and a mean age of 57 years. Escherichia coli is the most common causative pathogen, present in nearly 70% of the reported cases [1-2].

The clinical presentation of this life-threatening infection is non-specific. Frequently reported symptoms are fever, dysuria and flank pain, often mimicking a non-complicated pyelonephritis. Nevertheless, rapid progression to septic shock may occur [1-2].

Emphysematous pyelonephritis is a radiological diagnosis with CT as the preferred imaging technique. Ultrasound may show echogenic foci in the renal parenchyma or collecting system with an associated dirty-shadowing artefact. The presence of intraparenchymal, intracalyceal and/or intrapelvic renal gas on CT imaging is typical for emphysematous pyelonephritis. These intrarenal gas collections are often associated with perirenal collections consisting of fluid or gas. CT is the most sensitive imaging-modality and also allows us to further classify the infection based on the distribution of gas and the presence of fluid collections. The CT-classification according to Wan et al. and the more recent classification according to Huang and Tseng are commonly used to assess the severity and the associated mortality rate (Table 1) [2-5].

The survival rate increases if aggressive treatment of sepsis (with fluid resuscitation and antibiotics) and diabetic management are started as soon as possible. This conservative treatment, extented with early percutaneous drainage, is increasingly adopted. It is associated with higher survival rates than an emergency nephrectomy which should only be considered in patients with emphysematous pyelonephritis classes III-IV and a failure of conservative treatment [6].

In conclusion, emphysematous pyelonephritis is a rare but life-threatening infection which is diagnosed and classified by CT based on the typical appearance of intraparenchymal, intracalyceal and/or intrapelvic renal gas.