CHRONIC PYELONEPHRITIS

Chronic pyelonephritis
This is a confusing term. It can be a radiological or pathological diagnosis or description. The appearance pathologically or radiologically is one of renal scarring. The scarring can be due to previous infection or it can occur from the long-term effects of reflux (with or without superimposed infection). A child with reflux, particularly where there is reflux of infected urine, will develop reflux nephropathy (which if bilateral, may cause renal impairment or renal failure). If the child's kidneys are examined radiologically (or pathologically if they are removed by nephrectomy) the radiologist or pathologist will describe the appearances as those of  chronic pyelonephritis . An adult may also develop radiological and pathological features of chronic pyelonephritis, due to the presence of reflux, or bladder outlet obstruction combined with high bladder pressures, again particularly where the urine is infected. This was a common occurrence in male patients with spinal cord injuries and detrusor-sphincter dysynergia before the advent of effective treatments for this condition.

Essentially, then, chronic pyelonephritis is the end result of longstanding reflux (non-obstructive chronic pyelonephritis) or of obstruction (obstructive chronic pyelonephritis). These processes damage the kidneys leading to scarring, and the degree of damage and subsequent scarring is more marked if infection has supervened.

The scars are closely related to a deformed renal calyx. Distortion and dilatation of the calyces is due to scarring of the renal pyramids. These scars typically affect the upper and lower poles of the kidneys, because these sites are more prone to intrarenal reflux. The cortex and medulla in the region of a scar is thin. The kidney may be so scarred that it becomes small and atrophic. Scars can be  seen  radiologically on a renal ultrasound, an IVU, renal isotope scan, or a CT.