Chronic pyelonephritis

Chronic pyelonephritis is a form of pyelonephritis where there are longstanding sequelae of renal infection. At the time of writing there is still no definitive consensus as to whether the condition represents an active chronic infection, arises from multiple recurrent infections, or represents stable changes from a remote single infection, as radiographic differentiation between the above scenarios can be challenging.

Radiographic features

In general, bacterial infection results in focal scarring in the renal cortex overlying a calyx and is usually associated with some kind of calyceal distortion.

General

Imaging should be interpreted in the relevant clinical context and is often characterized by:

• renal scarring
• renal atrophy
• renal cortical thinning
• compensatory hypertrophy of residual normal tissue (which may mimic a mass lesion)
• calyceal clubbing: secondary to retraction of the papilla from overlying scar 
• thickening and dilatation of the calyceal system
• overall renal asymmetry

Complications

The long-term complications are not completely understood, but there does not appear to be an association with hypertension or progressive renal azotemia.

Practical points

Once the imaging changes of chronic pyelonephritis have been established, repeat imaging seldom provides new findings.