Pathology of the urinary system

HYDRONEPHROSIS

 

 

   ∙ 

an abnormal and permanent dilatation of the renal pelvis with progressive atrophy of renal 

parenchyma; can be unilateral or bilateral.   

   ∙ 

due to an increased pressure within the kidney following partial or complete obstruction of urine 

outflow at any level from the renal pelvis to the urethra.  

   ∙ 

urine outflow obstruction can be due to: 

 

  - 

congenital malformation (ureter, vesico-ureteral junction, urethra); 

 

  - 

calculi (pelvic or ureteral uroliths in cattle and rams, urethral urolithiasis in dogs and cats); 

 

  - 

chronic inflammation; 

 

  - 

neoplasia (e.g. transitional cell carcinoma of the bladder); 

 

  - 

iatrogenic (ligation of ureter during ovariohysterectomy). 

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   ∙ 

partial obstruction of the urethra can lead to hydronephrosis, but total obstruction more often causes 

rupture of the urethra (with leakage of urine into the surrounding tissues 

➝

 infection and acute 

cellulitis) or the bladder (

➝

 uroperitoneum / chemical [urine-induced] peritonitis). 

   ∙ 

pathogenesis: 

 

  - 

initially, glomerular filtration continues in spite of urine outflow obstruction, because the 

urine filtrate diffuses into the renal interstitium where it is absorbed by lymphatics and veins; 

 

  - 

over time, increased pressure throughout the parenchyma leads to pressure atrophy of tubular 

epithelium and occlusion of  blood vessels, particularly veins, by compression, causing 

papillary necrosis and further atrophy of renal parenchyma; 

 

  - 

it takes about 3 weeks of complete obstruction or several months of incomplete obstruction to 

produce irreversible renal damage. 

   ∙ 

grossly: 

  - 

dilatation of the pelvis with cortical atrophy and formation of thin-walled cysts filled with 

urine; 

  - 

in severe cases, the hydronephrotic kidney can appear as a fluid-filled balloon; 

  - 

urinary stasis predisposes to ascending bacterial infection 

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 suppurative inflammation may 

be superimposed on hydronephrosis or vice versa.