Chronic pyelonephritis.

CHRONIC PYELONEPHRITIS

• 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 scars overlying 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 :

1. Robbins and Cotrans: Pathologic basis of diseases.9th edition

2. Harshmohan: Text book of Pathology.7th edition