B78 Urinary outflow obstructions

Question 1

What are the causes of obstruction?

Answer 1

Congenital

• Urethra Atresia
• Ureterovesicular junction malformation
• Horshoe kidney compressing ureter

Acquired

• Nephrolithiasis
• Papillary necrosis and sloughed papillae
• Prostate obstruction,
  
  • prostatic hyperplasia
  • prostate cancer
  • porstatitis
• Carcinoma of the cervix or uterus
• Bladder tumors
• Inflammation, Urethritis, ureteritis, UTIs
• Neurogenic
  
  • Spinal cord damage
  • Diabetic nephropathy
• Normal pregnancy
  
  • often causes mild obstruction

Question 2

What are the 3 major types of kidney stones?

Answer 2

Calcium Oxalate and Calcium Phosphate

Struvite aka Magnesium Ammonium and Phosphate

Uric Acid

Question 3

What factors lead to kidney stone formation?

Answer 3

Supersaturatyion of the urine with any of the contents of the 3 types of stones. Also, possible caused by deficiency of inhibitors mineral precipitation: osteopontin, pyrophosphate, mucopolysaccharides, nephrocalcin glycoprotein.

Calcium-phosphate and Calcium oxalate stones:

• Most are idiopathic and not associated with hypercalcemia, probably due to excessive absorption or intake and prompt excretion of high amounts of calcium in urine.
• Others are associated with defects in calcium reabsorption
• Others are associated with hypercalcemia.

Struvite, Magnesium ammonium phosphate stones.

• Well understood, and always associated with UTIs that cause alkaline urine.
  
  • Proteus vulgaris with its urease increasing the urine pH.

Uric acid stones

• in 50%, caused by gout, diseases with high cell turnover and hyperuricemia
  
  • leukemias
• other 50%, have excessively acidic urine without an obvious reason
  
  • acidic urine favors uric acid stone formation.

Cystine stones

Cystine stones, form in specific genetic defects causing defecting renal transport of cystine, and form when urine is acidic.

Question 4

What are the consequences of kidney stones?

Answer 4

Large stones in the renal pelvis are very often totally asymptomatic

Small stones can lodge in the ureter causing:

• obstruction
• extreme pain, called renal or ureteral colic
• gross hematuria
• Predisposed to bacterial infection and pyelonephritis
• hydronephrosis

Question 5

What are the consequences of urinary outflow obstruction?

Answer 5

• Hydronephrosis
• Infections and pyelonephrosis
• Bilaterally if it is below the ureters.
• If it is in the ureter and unilateral, renal function is not compromised.
• There is usually still some urine flow even during obstruction and total anuria is rare.

Question 6

Describe the pathogenesis of damage to the kidney during outflow obstruction.

Answer 6

Dilation of the renal pelvis and calices.

Increased pressure causes compression of the renal vessels,

causes most severe dysfunction of the tubules, and impaired concentrating ability/water resorption.

Inflammation and eventual interstitial sclerosis.

It still takes a long time for irreversible damage to occur, about 3 weeks with total obstruction or 3 months with incomplete obstruction.

Unilateral obstruction causes damage to the affected kidney, but overal kidney function is in tact by the spared kidney and there is no azotemia.

On microscopic examination the early lesions show tubular
dilation, followed by atrophy and fibrous replacement of the
tubular epithelium with relative sparing of the glomeruli.

With sudden and complete obstruction,
there may be coagulative necrosis of the renal papillae,
similar to the changes of papillary necrosis

With mild chronic obstruction, there is extreme dilation of the calices, pelvis, and ureter.

Question 7

What is the clinical presentation of obstruction?

Answer 7

Bilateral complete obstruction produces anuria, which is
soon brought to medical attention. When the obstruction is
below the bladder, the dominant symptoms are those of
bladder distention.

Paradoxically, incomplete bilateral
obstruction causes polyuria rather than oliguria, as a result
of defects in tubular concentrating mechanisms, and this
may obscure the true nature of the disturbance.

Unfortunately,
unilateral hydronephrosis may remain completely
silent for long periods unless the other kidney is for some
reason not functioning. Often the enlarged kidney is discovered
on routine physical examination.