Chronic pyelonephritis is caused by bacterial infection associated with vesicoureteral reflux or obstruction.
It is disorder in which chronic tubulo interstitial inflammation & scarring involves the calyces and pelvis.
This is important cause of kidney destruction in children with severe lower urinary tract abnormalities
Etiopathogenesis:
Most common etiologic agent is Gram negative bacilli like Escherichia coli followed by proteus, klebsiella & enterobacter. Other agents ate streptococcus faecalis, staphylococci
In immunocompromised patients viruses like Polyoma virus, Cytomegalo virus and Adeno virus causes renal infection.
Chronic pyelopepritis is divided into two forms.
-Reflex nephropathy
-Chronic obstructive pyelonephritis
Reflex nephropathy:
More common form of chronic pyelonephritis is scarring
Reflux nephropathy occurs in childhood as a result of super imposition of urinary infection on congential vesicoureteral reflux and intrarenal reflux.
Reflex may be unilateral or bilateral
Chronic obstructive pyelonephritis:
Obstruction predisposes kidney to infection.
Recurrent infections superimposed on diffuse or localised obstructive lesions lead to repeated bouts of renal inflammation & scarring, resulting in chronic pyelonephritis.
It can by bilateral as in posterior uretheral valves or unilateral in case of calculi in ureter.
Mechanism by which microbes move from the bladder to the kidney
Urinary tract obstruction & stasis of urine
Normal organisms entering the bladder are cleared by continual voiding by antibacterial mechanisms.However outflow obstruction or bladder dysfunction results in incomplete emptying & residual urine.
In the presence of stasis, bacteria multiply unhindered.
This occurs when there is lower urinary tract obstruction, which may occur in BPH, tumours calculi or with neurogenic bladder dysfunction as in Db or spinal cord injury.
Vesicoureteral reflux:
Vesicoureteral reflux is the reflux of bladder urine into ureters due to incompetence of vesicoureteral valve which results in residual urine in urinary tract after voiding which favors bacterial growth
Bacteria ascends the ureter into the renal pelvis.
Reflux is most often due to congenital absence or shortening of the intravesical portion of the ureter. So that ureter is not compressed during micturition.
In addition bacterial infection and associated inflammation can promote reflux by affecting ureteral contracility, particularly in children.
Vesicoureteral reflux affects 1% to 2% of otherwise normal children.
Acquired vesicoureteral reflex in adults results from persistent bladder atony caused by spinal cord injury.
Intrarenal reflux:
Vesicoureteral reflux leads to the infected bladder urine to be propelled up to the renal pelvis and deep into the papillae (intrarenal reflex).
Intra renal reflux is common in the upper & lower poles of the kidney where papillae tend to have flattened or concave tips rather than the convex pointed type present in the midzones of the kidney.
In the absence of Vescico ureteral reflux, infection remains limited to bladder and urethra causing cystitis and urethritis.
Morphology:
Usually small and contracted kidney showing unequal reduction.
Gross:
Kidney are irregularly scarred
Hallmark of chronic pyelonephritis is coarse, discrete, cortico medullary scarsoverlying dilated, blunted or deformed calyces and flattening of the papillae.
U shaped depressions are present on cortical surface.
Scars vary from one to several and most are in the upper & lower poles, consistent with the frequency of reflex in the sites.
Microscopy:
Involves predominantly tubules & interstitium
Tubules:
The tubules show atrophy/hypertrophy and are dilated.
Dilated tubules are lined with flattened epithelium and may be filled with casts resembling thyroid colloid (thyroidization)
Interstitium:
Varying degrees of chronic interstitial inflammation & fibrosis in the cortex & medulla is noted.
Arcuate & interlobular vessels demonstrate obliterative intimial sclerosis in the scarred areas
In the presence of hypertension hyaline arteriosclerosis is seen in the entire kidney.
Fibrosis around the calyceal epithelium as well as marked chronic inflammatory infiltrate.
Glomeruli:
Glomeruli may be normal or shows periglomerular fibrosis, fibrous obliteration and secondary changes related to hypertension.
Focal segmental glomerulosclerosis occurs in individuals who develop proteinuria in advanced stages of chronic pyelonephrititis & reflux nephropathy.
Clinical features:
Chronic obstruction pyelonephritis may have a silent onset and may present with back pain, fever, pyuria & bacteriuria.
Patients present late in course with renal insufficiency & hypertension
Loss of concentrations ability gives rise to polyuria and nocturia.
Diagnosis:
Intravenous pyelography
Culture of urine may size positive results.
Reference :
Robbins and Cotrans: Pathologic basis of diseases.9th edition
