Urinary Tract Obstruction

• Increases susceptibility to infection and to stone formation
• Unrelieved obstruction can lead to permanent renal atrophy called hydronephrosis
• Obstruction may be sudden or insidious, partial or complete, unilateral or bilateral
• It can occur at any level of the urinary tract
• It can be intrinsic or extrinsic, whereby something compresses the ureter

 

Causes

• Congenital anomalies
  • Posterior urethral valves and urethral strictures
  • Meatal stenosis
  • Bladder neck obstruction
  • Severe vesicoureteral reflux
• Urinary calculi
• Benign prostatic hypertrophy
• Tumours
  • Prostatic carcinoma
  • Bladder tumours
  • Contiguous malignancy (retroperitoneal lymphoma)
• Inflammation
  • Prostatitis
  • Ureteritis
  • Retroperitoneal fibrosis
• Sloughed papillae or blood clots
• Normal pregnancy
• Uterine prolapse or cystocele
• Functional disorders
  • Neuropathic – dysfunctional obstruction

 

Hydronephrosis

• Dilation of the renal pelvis and calyces associated with progressive kidney atrophy due to obstruction of urine outflow
• Even with complete obstruction, glomerular filtration persists for sometime as the filtrate diffuses back into the interstitium and perirenal spaces and ultimately returns to the lymphatic and venous systems. The affected calyces and pelvis therefore becomes more dilated
• The high pressure in the pelvis is transmitted back through the collecting ducts into the cortex causing renal atrophy as well as compressing the renal vasculature of the medulla – decreasing intramedullary plasma flow
• The initial functional disturbances are therefore tubular resulting in impaired concentrating ability
• Later the GFR begins to diminish
• Obstruction also leads to interstitial inflammation which eventually leads to interstitial fibrosis

 

Morphology

• When obstruction is sudden, the reduction in glomerular filtration leads to mild dilation of the pelvis and calyces
• When obstruction is subtotal and intermittent, glomerular filtration is not suppressed and progressive dilation occurs
• Depending on the level of the obstruction, dilation may first be at the bladder, ureter or kidney
• Grossly the kidney may be slightly enlarged and there may be interstitial inflammation
• In chronic cases there may be interstitial fibrosis and cortical tubular atrophy
• Progressive blunting of the apices of the pyramids occur until they become cupped
• In very advanced cases the kidney way have transformed into a thin walled cystic structure having a diameter of 15-20cm with parenchymal atrophy, obliteration of pyramids and thinning of the cortex

 

Clinical course

• Acute obstruction may result in pain due to distension
• Calculi in the ureters may result in renal colic
• Prostatic enlargement may give rise to bladder symptoms
• Unilateral disease may remain silent whilst the other kidney compensates
• If the obstruction is removed early, within the first few weeks, the kidney can return to normal
• In bilateral partial obstruction, the earliest manifestation is the inability to concentrate urine reflected by polyuria
• Completel bilateral obstruction there is oligouria or anuria and this is incompatible unless obstruction is removed
• Often removal of obstruction there is a period of post-obstructive diuresis, where patients can loose large amounts of salt rich urine