Urinary Tract Obstruction and Urolithiasis

• Urinary tract obstruction is when there is a blockage in the urinary system
• Urolithiasis is the formation of stones in the urinary tract

Urinary Tract Obstruction Causes

• Urinary tract obstruction causes are multiple
• Intrinsic causes: nephrolithiasis, sloughed renal papilla, strictures, and cancer
• Extrinsic causes: carcinoma of the uterine cervix or endometrium, prostatic hyperplasia, retroperitoneal fibrosis, and retroperitoneal tumors

Urinary Tract Obstruction Prevalence

• Urinary tract obstruction appears more commonly in males than females during childhood
• Common causes for males include ureteropelvic or vesicoureteral obstruction
• Occurs more in females between childhood and age 60
• Most common cause for females is a gynecologic tumor
• After age 60 occurs in higher frequency in men due to prostatic disease

Pathophysiology of Urinary Tract Obstruction

• Pathophysiologic mechanisms for how urinary tract obstruction damages the kidney are:
  • Increased pressure into the medulla
  • Intrarenal reflux of urine
  • Direct pressure on blood vessels within the medulla

Clinical Features of Urinary Tract Obstruction

• Clinical picture of urinary tract obstruction varies greatly
• Bilateral partial obstruction can result in loss of ability to concentrate urine
• Sudden complete obstruction can result in acute renal failure

Treatment and Clinical Course of Urinary Tract Obstruction

• Treatment depends on the primary condition causing the obstruction
• Duration of obstruction is the most important factor in determining the degree of recovery

Formation of Renal Calculi

• Renal calculi formation depends on a balance of factors:
  • Concentration of the specific component (supersaturation)
  • Presence of nucleating factors such as epithelial cells, debris, or casts
  • Deficiency of stone inhibitors such as nephrocalcin, the Tamm-Horsfal protein, or citrate

Composition of Renal Calculi

• Calcium Oxalate stones accounts for about 75% of all renal calculi
• Struvite stones accounts for 10% to 15%
• Uric Acid stones accounts for 5% to 6%
• Cystine accounts for 1%
• Other forms account for about 15%

Types of Urolithiasis

• Most renal calculi are calcium oxalate stones
• Over half of renal calculi are associated with hypercalciuria without hypercalcemia
• About one fifth are associated with hyperuricosuria
• Magnesium ammonium phosphate stones are struvite calculi
• Struvite Stones associate with urea-splitting bacteria, often Proteus species
• Large staghorn calculi associate nearly always with Struvite stones
• For uric acid stones, majority of patients have neither hyperuricemia nor hyperuricosuria
• Stone formation in patients is believed to be a tendency to excrete urine with pH below 5.5 as uric acid is insoluble in acidic urine

Clinical Features of Urolithiasis

• Renal colic manifests as flank/groin excruciating pain
• Common symptoms also include nausea and vomiting
• Calculi may be painless if they remain in the pelvis
• Hematuria is a frequent manifestation

Clinical Course of Urolithiasis

• Smaller stones cause more complications because they pass into the ureter
• Calculi predispose to infection due to obstruction and trauma

Treatment of Urolithiasis

• Stones less than 5mm are likely to pass spontaneously
• Stones less than 2cm can often be treated with lithotripsy
• Larger stones may require nephrolithotomy