Morphological transition after medical treatment of emphysematous pyelonephritis over time-case report

Emphysematous pyelonephritis (EPN) is a necrotizing infection characterized by the production of gas in the renal parenchyma, collecting system or perirenal tissue. The treatment strategy, especially for surgical intervention, in EPN has been based on the Huang and Wan classifications. Huang's classification is based on the extent of gas and abscess spillover, while Wan's classification is based on the morphology of gas and fluid retention. Wan's classification type I EPN is considered more severe compared to type II EPN and pathophisyological mechanisms are speculated as the cause of the different presentation but the actual cause is unknown. In the present case, conservative treatment of EPN in the early stages of the disease allowed us to show that Wan's classification may represent a time series of morphologic changes throughout EPN.

A 72-year-old woman treated for diabetes was admitted because of suspected treatment-resistant pyelonephritis. Her CT scan at presentation was suggestive of EPN and antibiotics was started. After additional medical treatment, a follow-up of CT image showed that the initial appearance of bubbly gas formation changed into a fluid-forming abscess. This transition shows that type I is an early phase image of EPN and type II image is seen following the early phase. Thereafter no change was seen in CT image and residing inflammation led to planned nephrectomy on day 35. Antibiotics were discontinued and no recurrence was confirmed.

Wan's type I and II EPN has been often reported as different pathophysiological entities. Our case shows that these two subtypes may represent stages in the progression of EPN. Medical treatment for type I may permit safe nephrectomy for type II EPN.