Stones: Treatment Selection for Upper Urinary Tract Calculi

See 2016 AUA Stone Surgery Guideline Notes

Natural history

• The true natural history of renal calculi, particularly asymptomatic ones, has not been well characterized and it is unclear how to approach minimally symptomatic or asymptomatic renal calculi.
  • Although some small, asymptomatic renal stones may never require treatment, many will grow over time, become symptomatic, and ultimately require treatment
    • Risk of surgical intervention for initially asymptomatic stones: ≈10-20% at 3-4 years
    • Indications to treat small, asymptomatic stones
      • Children
      • Solitary kidney
      • High-risk professions (e.g. pilot)
      • Women considering pregnancy
      • Traveling to remote locating
      • Rapidly increasing in size

Pretreatment assessment

• History and Physical Exam
  • Identify conditions that predispose to nephrolithiasis (See Stone Epidemiology and Pathogenesis Chapter Notes
• Laboratory tests: urinalysis, lytes, Cr +/- CBC
  • Pre-operative urinalysis and culture are mandatory before any stone surgery, and positive cultures should prompt appropriate treatment before the day of surgery
    • Presence of crystals may reveal clues to underlying stone composition
    • Urine pH may add useful information when one is considering uric acid stones (low pH) or the presence of urease-producing bacteria (high pH)
  • Assessment of underlying renal function is necessary
  • Preoperative CBC should be obtained when PCNL or laparoscopic/open stone removal is contemplated
• Imaging

Stone factors: total stone burden, location, composition

• Total kidney stone burden
  • See 2016 AUA Stone Surgery Guideline Notes
  • Most important factor influencing treatment decisions
  • Classified as: < 1 cm vs. between 1 and 2 cm vs. > 2 cm
    • Kidney stone burden <1 cm
      • Almost all renal stones <1cm may be treated with SWL, URS, or PCNL.
        • SWL achieves stone-free rates of approximately 50-90%
          • Most studies have assessed stone-free outcomes using renal ultrasound or plain radiography (which has its limitations)
          • Successful clearance with SWL is highest for stones in the renal pelvis and ureteropelvic junction (UPJ 80-88%), favorable for stones in the upper and middle calyces (70%), and consistently less for lower poles stones (35-69%)
        • The greater invasiveness and higher rate of significant complications of PCNL limit its widespread adoption to the treatment for these stones
          • PCNL should be used for stones that have failed less invasive treatment modalities (SWL or URS) or are extremely large or dense.
        • The outcomes of PCNL and URS are independent of the patient’s BMI, whereas SWL success falls with increasing obesity
    • Kidney stone burden between 1 and 2 cm
      • PCNL has higher stone-free rates and requires fewer additional procedures than SWL or URS for kidney stones between 1-2cm. However, PCNL is more invasive and has higher risk of complications compared to SWL and URS.
    • Kidney stone burden > 2 cm
      • PCNL should be considered first-line therapy for kidney stone burdens >2 cm
        • In patients with significant comorbidities or contraindications to PCNL are present (frailty, coagulopathy, refusal of transfusion), less invasive alternatives such as URS, though less efficient and potentially requiring multiple stages, should be considered.
          • URS may be safely performed in patients with active anticoagulation or antiplatelet therapy.
  • Staghorn stones
    • No standard definition exists for complete and partial staghorn stones, though most consider complete staghorn stones to occupy the entire renal collecting system, whereas partial staghorn stones occupy less.
    • Struvite composes the majority of staghorn stones.
    • PCNL is the method of choice for treating partial or complete staghorn kidney stones
      • Poorly or nonfunctioning kidneys and those associated with xanthogranulomatous pyelonephritis may be best managed with nephrectomy
      • Best approached through upper or lower polar access
    • Observation and non-operative management should be discouraged, because the natural history of untreated staghorn stones is associated with (3):
      1. Complete loss of function in the affected kidney
         • Complete renal function loss in 50% of affected kidneys can occur after 2 years without treatment
      2. Recurrent UTIs and sepsis episodes
      3. Increased overall mortality
  • Open nephrolithotomy is reserved for rare instances where complicating factors make PCNL impossible or unlikely to achieve reasonable stone clearance within an acceptable number of combination of procedures
  • No change in long-term renal function from SWL, multiple URS, or single-access tract PCNL
    • The effects of multi-access tract PCNL on renal functional outcomes are mixed
• Stone location
  • Second most important consideration
  • Classified as lower pole stones vs. non-lower pole stones
  • Lower pole stones tend to prove the most difficult to treat and are more difficult to clear with URS or SWL, and therefore stones ≥1 cm within the lower pole may be most efficiently treated with PCNL.
  • Stones in a non-lower pole location tend to respond more readily to SWL and URS, making those techniques more competitive with PCNL.
    • However, excellent clearance with URS has been reported for all renal stones, suggesting that stone size and density, along with patient anatomy, are more important factors than intrarenal stone location when considering URS treatment decisions
    • For PCNL, stones within the middle calyx and renal pelvis are more likely to be cleared than stones in upper or lower calyceal locations
  • Lower pole calculi
    • Treatment decisions are further divided into stone burdens < 1 cm, between 1 to 2 cm, and > 2 cm.
    • Lower pole kidney stone burdens ≥2 cm
      • Best approached with PCNL because PCNL offers a considerably higher stone-free rate in a single procedure than URS or SWL.
    • Lower pole stone burdens of 1 cm to 2 cm
      • PCNL remains the most efficient treatment option, although it is more invasive, and is preferred when prior URS or SWL attempts have been unsuccessful.
        • Ureteroscopy is the treatment modality of choice when PCNL is completely or relatively contraindicated and is a reasonable first-line option in experienced hands.
      • SWL should not be recommended as an initial treatment modality
        • In general, SWL results are disappointing for lower pole stone burdens ≥; 1 cm
    • Lower pole stones <1 cm
      • May be reasonably approached with any modality including observation if completely asymptomatic, although future stone disease progression is likely.
      • Stone characteristics and patient factors become relatively more important than for larger stone burdens and should be incorporated into treatment recommendations.
    • Lower pole anatomic features that may reduce stone passage after SWL
      1. Narrow lower pole infundibulum (width <4 mm)
      2. Acute lower pole infundibulopelvic angle (<90 degrees)
      3. Multiple lower pole infundibula rather than a single infundibulum
    • Percussion, diuresis, and inversion are safe, well tolerated, and modestly aid in stone passage after SWL

• Stone composition
  • Affects success rates with SWL; URS, PCNL, and laparoscopic and open stone surgery are less affected by stone composition, if at all.
    • Therefore, factoring stone composition into treatment decision analysis is most relevant for stones ≤2 cm or less in size, for which SWL is often considered first-line therapy or as a first-line therapeutic option.
    • Stone compositions most resistant to SWL (in descending order) (4):
      1. Cystine
      2. Calcium phosphate (specifically “brushite”)
      3. Calcium oxalate monohydrate
      4. Matrix
         • PCNL is the preferred treatment approach for matrix renal stones owing to its high success rates and recurrence rates
    • In vitro studies have shown that holmium laser lithotripsy fragmentation efficiency is also dependent on stone composition, with the poorest fragmentation seen for the calcium oxalate monohydrate stones and moderate fragmentation seen for uric acid and cystine stones

Patient factors

• Renal function
  • Symptomatic upper tract stones located in renal units with <15% split function (different thresholds in literature) should be considered for nephrectomy, and stone-specific, nephron-sparing treatments should not be pursued.
• Renal anatomic factors
  • Ureteral pelvic junction obstruction
    • A variety of strategies can be used to treat renal stones with concomitant UPJO (3):
      1. PCNL with antegrade endopyelotomy
      2. Retrograde endopyelotomy with URS stone removal
      3. Pyeloplasty (laparoscopic or robotic) with pyelolithotomy or nephrolithotomy
  • Calyceal diverticula
    • Urothelium-lined, non-secretory, cystic dilations of the intrarenal collecting system that are thought to arise embryonically.
    • Associated with poor urine drainage
    • A large percentage of calyceal diverticula are asymptomatic
    • Management
      • Asymptomatic diverticular stones require no treatment
      • Indications for intervention: diverticular stones associated with
        1. Pain
        2. Recurrent infections
        3. Hematuria
        4. Decline in renal function warrant treatment
      • Approach:
        • Options: PNCL (preferred) vs. URS (no SWL)
          • Choice depends on both stone and diverticular anatomic characteristics
          • PCNL should be considered first-line treatment for most calyceal diverticular stones
            • Directly puncturing into the calyceal diverticulum is preferable and allows for stone fragmentation and removal, easy fulguration of the diverticular lining, and dilation of the diverticular neck if visible and desired
              • Ablation of the calyceal diverticular lining, dilation of the diverticular neck to improve drainage, or both are considered integral to achieving stone clearance and preventing stone recurrence
          • URS is a reasonable first-line treatment approach for patients with small (<2 cm) calyceal diverticular stones arising from an upper or middle calyx, and with a diverticular neck that is short and identifiable
            • For stones in an anterior calyceal diverticulum, URS is prefererred over PNCL due to the high risk of bleeding associated with PNCL into an anterior calyx
          • SWL is seldomly successful for diverticular stones and should not be considered first-line therapy for most symptomatic diverticular stones
  • Horseshoe Kidneys and Renal Ectopia
    • Horseshoe Kidneys
      • Embryonically, the abnormal medial fusion of the left and right metanephric blastemata creates an isthmus that anchors the fused kidneys at the level of the inferior mesenteric artery, leading to incomplete renal ascent and malrotation. As a result, the:
        1. Renal pelvis becomes elongated and anteriorly located
        2. UPJ has a high insertion into the renal pelvis and is also anteriorly situated
        3. Proximal ureter courses more anteriorly than usual because it must traverse over the isthmus of the horseshoe kidney.
        • Collectively, these changes are thought to impede normal urinary drainage and promote urinary stasis and renal stone formation
    • Management
      • SWL is a reasonable treatment option for stone burden < 1.5 cm and there is no UPJO or demonstration of poor renal drainage
        • UPJO and poor pelvicalyceal drainage must be excluded before SWL treatment
          • These are not uncommon in horseshoe kidneys and severely impede SWL success
          • Pelvic kidneys are routinely malrotated and often have a high ureteral insertion or UPJO, which can further hinder stone fragment passage
      • URS may also be reasonable for stone burden < 2 cm, although they may require multiple treatment sessions.
        • During URS, fragmented stones should be basket extracted rather than left in situ and left to pass spontaneously, given the often compromised drainage associated with horseshoe kidneys
      • For stone burdens of ≥2 cm, PCNL or laparoscopy should be the initial treatment; a combination of the two procedures is expected for pelvic kidneys
        • PCNL stone clearance and complications rates are the same for horseshoe kidney compared to orthotopic kidney.
          • A retroreneal colon may accompany horseshoe kidneys, and a preoperative CT is recommended to fully evaluate the safest percutaneous track.
      • When UPJO is confirmed, laparoscopy is the treatment of choice because it can address the stones and provides the highest success rate for UPJ repair.
  • Renal transplants
    • SWL
      • An option for stones in transplant kidneys <1.5 cm; however, high re-treatment rates and auxiliary procedure rates should be expected
    • URS
      • Antegrade and retrograde URS can be used to treat transplant kidney and ureteral stones.
    • PCNL
      • The preferred treatment choice for large-burden stones (>1.5 cm) or if less invasive methods have failed.
    • The general consensus is to remove upper tract stones within renal transplants, as the consequences of an obstructing stone can be devastating
    • In transplanted kidneys, typical renal colic does not occur because the transplanted kidney and ureter are denervated. The presentation may instead resemble acute rejection or acute tubular necrosis
  • Prior renal surgery
    • Not a contraindication to any form of renal stone surgery.

Ureteral calculi

• Diagnosis and Evaluation
  • History and Physical Exam
    • History
      • New-onset urgency and frequency may indicate a stone at the UVJ irritating the bladder, or the sudden relief of flank pain might indicate either passage or forniceal rupture as the pressure in the collecting system dramatically decreases.
• Management
  • Observation
    • If the ureter is not otherwise obstructed, the main determinant of stone passage is the axial diameter of the stone
      • Second most important determinant is the location of the stone within the ureter at presentation
      • Other factors that may influence interval to stone passage include:
        • Laterality (right side more likely to pass)
        • Duration of symptoms before presentation
        • Degree of hydronephrosis
      • Stone composition has not been shown to influence interval to stone passage
    • Active stone treatment is indicated when obstruction has persisted for ≈4 weeks. Continued renal blockage after this time may lead to irreversible kidney damage
  • Intervention
    • SWL and URS are both considered first-line therapies for stones at all locations within the ureter, although a higher rate of ancillary procedures should be expected with stones >1cm.
      • Ureteroscopy is the most cost-effective treatment strategy for ureteral stones at all locations, after observation fails.
    • A percutaneous and antegrade approach may be used for very large proximal ureteral calculi not amenable to SWL or URS
    • If a ureteric stricture is present, can perform open, laparoscopic, or robotic-assisted laparoscopic treatment for both the stricture and the stone in the same session

Evaluation of Outcome

• Comparison of outcomes between endourologic stone treatment types is difficult due to varried definitions of success
  • Since the introduction of SWL, treatment outcomes for patients with renal calculi have been reported by two different terms: stone-free rate and success rate.
  • The stone-free rate is self-explanatory, but the success rate includes patients who are stone free as well as those with clinically insignificant residual fragments.
    • Definition of clinically insignificant residual fragments (CIRF): fragments between 2-4 mm.
  • These different methods of reporting treatment results, the lack of a standard definition for CIRF, and the various modalities used for assessing postprocedural stone-free status (KUB studies, nephrotomography, ultrasonography, CT) make the comparison of endourologic stone outcomes difficult

Questions

1. What stone burden threshold is considered an indication for PCNL in renal transplant patients?

Answers

1. What stone burden threshold is considered an indication for PCNL in renal transplant patients?
   • >1.5 cm

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 52