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Pyelonephritis
Introduction:
Pyelonephritis is a common suppurative inflammation of the kidney and renal pelvis caused by bacterial infection. Pyelonephritis is usually associated with an infection of lower urinary tract and occurs more frequently in females. Bacteria infect the kidneys via the bloodstream and from the lower urinary tract
Pathophysiology:
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· An ascending infection from the ureter is the most important route and results from the reflux of bacterial-contaminated urine (vesicoureteral reflux) from the lower urinary tract.
· Vesicoureteral reflux occurs more readily with an uretheral obstruction or cystitis as the urinary bladder pressure is increased and the normal vesicoureteral valve is compromised.
· Hematogenous infection is less common and results from seeding of the kidneys due to septicemia or bacterial endocarditis
· Placement of urinary catheters, pregnancy and diabetes increase the likelihood of urinary tract infections.
· Bacteria that reach the pelvis infect the medulla and the collecting ducts, causing tubular epithelial necrosis, hemorrhage, and stimulate an inflammatory response.
· Enteric Gran-negative rods, such as E. coli (most important), Proteus, Klebsiella, Enterobacter, and Pseudomonas are the principal causative agents. Fig. 14-13, page 456, Chapt 14 in: Basic Pathology, 6th ed. Kumar, V., Cotran, R., Robbins, S.L. W.B. Saunders, 1997.
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Clinical Signs and Clinical Pathology:
lumbar or abdominal pain
chills, fever, malaise
pyuria, bacteriuria, hematuria or granular casts from urinalysis
Gross pathology:
In animals with acute pyelonephritis, the kidneys may be enlarged, but chronic
pyelonephritis appears as shrunken, irregular kidneys. The kidneys show discrete, yellow or pale,
raised abscesses on the renal surface with infarction and scarring in some animals. The pelvic and ureteral
mucosal surfaces may be inflamed, thickened, reddened or granular and coated with exudate.
Histopathology:
Necrosis, fibrin, neutrophils and bacteria are on the surface. Renal interstitium may contain neutrophils, hemorrhages and edema. Papillitis, pyelitis and interstitial nephritis are seen.
Diagnosis:
Ultrasonography or excretory urography are the best diagnostic methods for
pyelonephritis. Ultrasonographic findings of pyelonephritis are dilation of the
renal pelvis and ureter with a hyperechoic mucosal line. Excretory urography
reveals dilation of the renal pelvis and proximal ureter with a lack of filling
of the collecting diverticula.
For more information:
Kumar, V., Cotran, R., Robbins, S.L. 1997. Pyelonephritis: Chapter 14: The Kindey and Its Collecting System. In: Basic Pathology, 6th ed. W.B. Saunders pp: 455-458.
Nelson, R.W., Couto, C.G., et al. 1998. Urinary Tract Infections. In: Small Animal Internal Medicine. Mosby pp. 630-637.
Tilley, L.P., and Smith, F.W. 2000. Pyelonephritis. In: The Five Minute Veterinary Consult Canine and Feline. Williams and Wilkins pp. 994-995.
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