- Two general mechanisms exist through which repeated cases of renal interstitial infection might occur. "Congenital Reflux" occurs in children who possess anatomical defects of the kidneys and urinary tract which prediposes to reflux of urine into the renal interstitium, thus causing repeated infections. "Chronic Obstruction involves long-term, uncorrected urinary tract obstruction that yields chronic backup of urine into the renal interstitium, thus allowing for repeated bouts of infection. Whatever the pathogenic mechanism, repeated infections followed by healing result in scarring and atrophy of the renal interstitium.
- Gross Appearance
- The kidney demonstrates irregular deformities characterized by corticomedullary scars with adjacent disfigured renal calyces. Because intra-renal reflux of urine tends to occur in the upper and lower poles, these are the areas of the kidney where scarring is most prominent.
- Histological Appearance
- Tubules may be atrophied or dilated and filled with proteinacious material giving an appearance similar to thyroid follicles, termed "Thyroiditization". Scarring is characterized by extensive fibrosis of the renal interstitium and calyces.
- Chronic Pyelonephritis may come to attention during an episode of acute pyelonephritis with its attendant constitutional symptoms, flank pain, bacteruria, and pyuria. However, in many instances chronic pyelonephritis occurs insidiously and silently over many years and only comes to attention when chronic renal failure results.