Stones: Lower Urinary Tract Calculi

Bladder Stones

• Classification: primary vs. secondary

Primary bladder calculi

• Bladder stones that develop in the absence of any known functional, anatomic, or infectious factors
• Epidemiology
  • 9-33 times more common in boys
• Pathogenesis
  • More common in children exposed to low-protein, low-phosphate diets
    • Lack of protein leads to a dietary phosphate deficiency, low urinary phosphate, and high levels of urinary ammonia. Due to this, the most common stone found in children from these areas is ammonium acid urate
  • Generally not associated with anatomic, functional, or infectious abnormalities.
• Generally, a solitary stone
• Management
  • Prevention consists mostly of dietary modification
  • Rarely recur after treatment

Secondary bladder calculi

Risk factors

1. Bladder outlet obstruction (most common cause)
   • Associated with decreased fluid intake with the resultant production of concentrated acidic urine
2. Neurogenic or spinal cord injury
   • Intermittent catheterization decreases the risk of bladder stone formation in comparison to an indwelling catheter.
   • Suprapubic provides no benefit compared to urethral catheterization in terms of the development of bladder calculi
3. Augmented bladders and urinary diversion
   • The incidence of bladder calculus after augmentation cystoplasty ranges from 10-52.5%
     • High risk of stone formation due to (6):
       1. Metabolic abnormalities
       2. Recurrent infections with urease-splitting organisms
       3. Prolonged urinary stasis and incomplete bladder emptying
       4. Prolonged exposure of urine to non-absorbable materials
       5. Anatomical changes following diversion
       6. Reflux of mucous into the upper tract
     • Most common stone types are magnesium ammonium phosphate (struvite) and calcium phosphate
     • The role of intestinal mucus in stone formation remains controversial
   • Unlike the nonaugmented population, females who have undergone augmentation cystoplasty are more likely to develop bladder calculi than males, likely owing to the higher incidence of cloacal abnormalities, which require additional procedures to establish continence.
4. Kidney or pancreas transplant
   • Risk factors for stone formation
     1. Nonabsorbable suture material used for the anastomosis.
     2. Incomplete bladder emptying due to diabetic cystopathy.
     3. Bacteriuria associated with included duodenal segments.
     4. Metabolic acidosis due to bicarbonate leak

In contrast to renal stones, bladder stones in adults are usually composed of uric acid (in non-infected urine) or struvite (in infected urine).

• Calcium oxalate or cystine stones in the bladder suggests the ureteral passage of calculi originating in the kidney with subsequent entrapment in the bladder

Diagnosis and Evaluation

• History and Physical Exam
  • The most common presenting symptom of bladder calculi is gross hematuria, which generally is terminal
• Imaging
  • Plain film
• Cystoscopy
  • Most accurate examination to document the presence of a bladder calculus.
  • Can assist in surgical planning by identifying prostatic enlargement, bladder diverticulum, or urethral stricture that may need correction before or in conjunction with the treatment of the stone.

Management

• Best managed with endoscopic techniques.
  • Transurethral endoscopic management is generally considered safe in augmented bladders, regardless of the type of substitution performed.
  • Holmium laser lithotripsy has become the modality of choice, owing to its ability to treat large calculi while incurring a minimum of collateral damage
  • Endoscopic management through a continent catheterizable (e.g. Indiana, Mitrofanof, etc.) conduit is not advised, because disruption of the continence mechanism can occur
    • Percutaneous cystolithotomy (i.e. PCNL of bladder) is highly successful in clearing bladder stones and might be less traumatic than transurethral approaches
    • Although percutaneous intervention is generally advised for the treatment of stones in patients with pouch diversions, the large caliber of the catheterizable limb and the nipple valve of the Kock pouch will tolerate endoscopic instrumentation.
  • No role of medical therapy in bladder stones.
• Subsequent recurrence is prevented by relief of the bladder outlet obstruction.

Prostatic calculi

• Believed to arise as a result of inspissation of prostatic secretions within the prostatic ducts
  • Majority are found in the posterior and posterolateral zones of the prostate, along the course of large prostatic ducts; large stones are rarely found within the central zone.
  • Generally composed of calcium phosphate and calcium carbonate
• Typically asymptomatic; however, there have been rare cases of exceptionally large calculi causing urinary tract obstruction
• Serum prostate-specific antigen levels are unaffected by the presence of prostate calculi.

Urethral calculi

• A urethral diverticulum is present in nearly all reported cases of urethral calculi in females
• In instances of prolonged delays in diagnosis, urethrocutaneous or urethrorectal fistulae may develop
• Management
  • Largely determined by the location within the urethra, as well as by the presence of an associated anatomic pathologic process such as a diverticulum.
  • Stones located in the posterior urethra may be pushed back into the bladder for subsequent fragmentation. For stones in the anterior urethra, retrograde relocation to the bladder is rarely feasible and should therefore not be attempted.

Preputial calculi

• Virtually all cases of preputial calculi are associated with severe phimosis in uncircumcised males
• All symptoms typically completely resolve after circumcision and calculus removal

Questions

1. Which patients are at risk of forming primary bladder calculi?
2. What is the typical composition of secondary bladder calculi?
3. When should endoscopic management of bladder calculi be avoided?
4. What abnormality is commonly associated with urethral calculi?
5. What are potential complications of an untreated urethral calculus?
6. What is the treatment of preputial calculi

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 55