Plain CT scan of the abdomen demonstrates bilateral renal enlargement. There is evidence of gas within the renal parenchyma and perirenal space. Gas and fluid collections representing abscesses involve the right Psoas. The perirenal and lateroconal fasica is thickened.
Discussion: Emphysematous pyelonephritis (EPN) is a severe form of bacterial pyelonephritis produced by organisms of the lower GI tract, particularly E. coli. Gas production (predominantly CO2 and H2) occurs outside the bacteria in necrotic tissue and results from fermentation of glucose by the organisms. The condition occurs twice as often in females as in males and is most commonly seen in diabetic patients (more than 80% of cases) and non-diabetic patients with obstruction. The patient often presents with symptoms of genitourinary sepsis.
Plain film and CT diagnosis of EPN is quite easy – both typically demonstrate scattered, streaky collections of gas, often conforming to the renal fossa, psoas muscle, or adjacent fascial boundary. Contrast enhanced CT more specifically delineates the extent of disease within retroperitoneal compartments, associated abscess, and relative function of the affected kidney, which are all important in making management decisions and in prognosis.
Though in the emergency room, ultrasound is the first imaging procedure – it is not clear cut in USG. Findings on USG range from a featureless kidney with multiple , subtle echogenic foci with ‘dirty shadowing’ artifacts to ‘absence’ of the kidney as a result of widespread gas. As in uncomplicated pyelonephritis, the kidney may be enlarged and demonstrate areas of abnormal, especially decreased echogenicity.
A radiographic staging system for EPN has been suggested. According to this system, Type 1 EPN consists of parenchymal destruction with mottled or streaky gas and the absence of renal/perirenal fluid collections. In Type 2 EPN there are renal/perirenal fluid collections with associated gas or collecting system gas. Type 1 EPN appears to have a more aggressive course and carries a 69% mortality rate. Type 2 EPN has a more prolonged course and a lower (18%) mortality rate.
Treatement consists of emergency nephrectomy often with drainage.
Dr Santosh Rai