Stones: Treatment Selection for Upper Urinary Tract Calculi

See 2016 AUA Stone Surgery Guideline Notes

Natural history

• Debate exists about the true natural history of renal calculi, particularly asymptomatic ones, and it is unclear how to approach minimally symptomatic or asymptomatic renal calculi.
  • Risk of surgical intervention for initially asymptomatic stones: ≈10-20% at 3-4 years
    • Sorenson et al. NEJM 2022[1]
      • Population: 73 patients with scheduled to undergo endoscopic surgical treatment (ureteroscopy or PCNL) of a primary stone at the urology clinics of the participating large, urban, tertiary-care centers, with one or more secondary stones on computed tomography (CT)
        • Primary stones defined as those located within the ureter or a kidney and that produced symptoms or were considered at high risk of causing an adverse clinical event
        • Secondary stones defined as small (≤6 mm), asymptomatic renal stones that were:
          • Located in the contralateral kidney (in the case of a primary renal stone) OR
          • In either kidney (in the case of a primary ureteral stone, with the specific kidney identified before randomization)
        • Patients with known systemic disease or anatomical disorders such as medullary sponge kidney, primary hyperparathyroidism, renal tubular acidosis, sarcoidosis, and horseshoe kidney were excluded.
      • Randomized to treatment vs. control of secondary stones
        • Secondary stones in patients in the treatment group were removed by ureteroscopy
      • Results
        • Baseline characteristics
          • Median secondary stone size: 3 mm treatment vs. 4 mm control
          • Median number of secondary stones: 1 treatment vs 1 control
        • Outcomes
          • Primary: relapse in each group, defined according to any of 3 measures:
            1. Emergency department visit owing to stones on the same side where the original asymptomatic stone had occurred (trial side) during the follow-up period (2 weeks to 5 years after surgery)
            2. Subsequent surgery to remove stones on the trial side in the follow-up period
            3. Growth of an original secondary stone, as measured with the use of CT.
               • Stone growth defined as an increase in stone size of more than 1 mm in one dimension or 1 mm or more in two dimensions, as measured by subsequent CT scans.
      • Results
        • Treatment group had significantly fewer relapses than the treatment group (relapse rate 16% treatment vs. 63% control)
      • Sorensen, Mathew D., et al. "Removal of small, asymptomatic kidney stones and incidence of relapse." New England Journal of Medicine 387.6 (2022): 506-513.
  • Relative indications to treat small, asymptomatic stones (6):
    1. Children
    2. Solitary kidney (including renal transplants)
    3. High-risk professions (e.g. pilot)
    4. Women considering pregnancy
    5. Traveling to remote locating
    6. Rapidly increasing in size

Investigations Prior to Treatment★

UrologySchool.com Summary

• History and Physical Exam
• Laboratory:
  • Mandatory (1): urinalysis +/- culture
  • Certain situations (4):
    • Serum electrolytes
    • Serum creatinine
    • CBC
    • Coagulation profile
• Imaging
  • Non-contrast CT
    • Should be obtained prior to PCNL
    • Can help select between SWL vs. URS (decision should not be based on US)
  • Certain situations: functional imaging, other contrast enhanced studies

Laboratory

• Urinalysis +/- culture
  • Required prior to intervention
  • In patients with clinical or laboratory signs of infection, urine culture should be obtained
    • If the culture demonstrates infection, appropriate antibiotics should be prescribed based on sensitivity
    • There can be discordance between preoperative voided urine cultures or those from indwelling urethral catheters compared to urine proximal to an obstructing stone.
      • Intraoperative urine cultures should be obtained, if technically feasible, from urine proximal to the stone if infected urine is suspected at the time of intervention.
    • Additionally stone cultures may be obtained, especially in cases of suspected infection-related stones, in order to help guide postoperative therapy.
      • There is also potential discordance between stone cultures and preoperative voided urine cultures
  • 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)

• Serum electrolytes and creatinine
  • Should be obtained if there is suspicion of reduced renal function
    • Reduced renal function is suspected in those with hydronephrosis, parenchymal thinning or co-morbid conditions associated with renal dysfunction and electrolyte disturbances
• CBC and platelet count
  • Should be obtained for patients:
    1. Undergoing procedures where there is a significant risk of hemorrhage (e.g. PCNL)
    2. With symptoms suggesting anemia, thrombocytopenia, or infection
• Coagulation studies
  • In the absence of clinical indications (e.g., systemic anticoagulation, relevant hepatic dysfunction, hematologic disease or bleeding disorders, history suggestive of a coagulation disorder) coagulation studies should not be routinely obtained prior to surgical management of urinary stone disease

Imaging

• Non-contrast CT
  • CT protocols have been developed and evaluated utilizing radiation doses approximating those of plain film radiography.
  • Should be obtained prior to performing PCNL
    • Defines stone burden and distribution
    • Provides information regarding collecting system anatomy, position of peri-renal structures and relevant anatomic variants
    • May be used to predict stone composition
    • May be used to predict operative outcomes
  • May be used to help select the best candidate for SWL vs. URS
    • Ultrasound alone to select SWL vs. URS should be discouraged
      • Disadvantages of US:
        • Provides no information on stone density
        • Inaccurate in determination of stone size
          • US will correlate approximately 2/3 of the time with the stone size determined on CT scan.
            • US will overestimate the size of 1/3 of stones < 10 mm, and underestimate the size of 1/3 of stone, > 10 mm.
            • KUB underestimates > 90% stones > 10 mm due in part to its inability to measure in three dimensions
    • Factors associated worse SWL outcomes:
      • Renal stone attenuation >900-1000 Hounsfield units
      • Skin-to-stone distance >10cm
• Functional imaging study (DTPA or MAG‐3)
  • May be obtained if clinically significant loss of renal function in the involved kidney(s) is suspected
• Additional contrast imaging may be obtained if further definition of the anatomy is needed
  • Situations in which complex urinary tract anatomy may require further imaging include:
    • Ectopic kidneys (e.g., horseshoe kidney, pelvic kidney, cross-fused ectopia)
    • Other congenital kidney conditions (e.g., UPJ obstruction, duplicated collecting system, caliceal diverticulum, ureteral stricture, megaureter, ureterocele),
    • Renal transplant grafts
    • Kidneys with prior surgery
    • Complex stone anatomy/conditions (e.g., staghorn stones, nephrocalcinosis).
  • Further imaging may be required in certain patients (e.g., neurologic disorders, including spinal dysraphism; unusual body habitus; presence of urinary diversion or prior kidney/ureteral surgery)
  • CT and IVP are the most useful IV contrast studies
    • MR urography can be useful in defining anatomy during pregnancy (without contrast) and in the setting of IV contrast allergy, although stones are typically not well visualized directly with MR imaging
    • Contrast imaging studies can also include retrograde or antegrade pyelography

Management of Ureteric Stones

Diagnosis and Evaluation

• History and Physical Exam
  • History
    • New-onset urgency and frequency may indicate a stone at the UVJ irritating the bladder
    • Sudden relief of flank pain may indicate either passage or forniceal rupture as the pressure in the collecting system dramatically decreases.

Management

Observation

• If the ureter is not otherwise obstructed (e.g. from ureteric stricture distal to stone), 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

Management of Renal Stones

Treatment Selection

• Factors to consider when selecting treatment for kidney stones:
  1. Presence of symptoms
     • Observation may be appropriate for select, asymptomatic stones
  2. Stone factors
     1. Total stone burden
     2. Stone location
     3. Stone composition
  3. Patient factors
     1. Anticoagulation
     2. BMI
     3. Renal function
     4. Renal anatomic factors

Stone factors

• Classified as (3):
  1. Total stone burden
  2. Stone location
  3. Stone composition

Total kidney stone burden

• See 2016 AUA Stone Surgery Guideline Notes
• Most important factor influencing treatment decisions
• Classified as (3):
  1. < 1 cm
  2. ≥ 1 and ≤ 2 cm
  3. > 2 cm

Kidney stone burden <1 cm

• Options (3):
  1. SWL
  2. URS
  3. PCNL
     • SWL for kidney stone burden < 1cm
       • Stone-free rates: ≈50-90%
         • Most studies have assessed stone-free outcomes using renal ultrasound or plain radiography, which have limited sensitivity to detect small stones
         • Successful clearance with SWL is dependent on stone location:
           • Highest for stones in the renal pelvis and ureteropelvic junction (UPJ 80-88%)
           • Favorable for stones in the upper and middle calyces (70%)
           • Consistently less for lower poles stones (35-69%)
     • PCNL for kidney stone burden < 1 cm
       • Invasiveness and higher rate of significant complications of PCNL limit its widespread adoption in the treatment of kidney stone burden <1 cm
         • PCNL should be used for stones that have failed less invasive treatment modalities (SWL or URS) or are extremely large or dense.

Kidney stone burden ≥ 1 and ≤ 2 cm

• Options (3):
  1. SWL
  2. URS
  3. PCNL
• PCNL for kidney stone burden ≥ 1 and ≤ 2 cm
  • Higher stone-free rates and requires fewer additional procedures than SWL or URS
    • 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.

Staghorn stones

• No standard definition exists for complete and partial staghorn stones
  • Most consider complete staghorn stones to occupy the entire renal collecting system, whereas partial staghorn stones occupy less.
• Majority of staghorn stones are struvite in composition.
• PCNL is the method of choice for treating partial or complete staghorn kidney stones
  • Best approached through upper or lower polar access
  • Poorly or nonfunctioning kidneys and those associated with xanthogranulomatous pyelonephritis may be best managed with nephrectomy
• Observation and non-operative management is discouraged
  • Natural history of untreated staghorn stones (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

• 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

Stone location

• Second most important consideration
• Classified as (2):
  1. Lower pole stones
  2. Non-lower pole stones

Lower pole stones

• Treatment decisions are further divided into stone burdens
  1. < 1 cm
  2. ≥ 1 and ≤ 2 cm
  3. > 2 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 stone burdens ≥ 1 and ≤ 2 cm
  • Options (2):
    1. PCNL
    2. URS
  • PCNL remains the most efficient treatment option
    • 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.
    • Although PCNL 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 kidney stone burdens ≥2 cm
  • PCNL is the preferred approach
    • PCNL offers a considerably higher stone-free rate in a single procedure than URS or SWL.
• 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

Non-lower pole stones

• Options (3):
  1. SWL
  2. URS
  3. 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

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

Anticoagulation

• URS may be safely performed in patients with active anticoagulation or antiplatelet therapy.

Body mass index

• PCNL and URS stone-free outcomes are independent of the patient’s BMI, whereas SWL success falls with increasing obesity

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.
• 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

Renal anatomic factors

Ureteral pelvic junction obstruction

• Options 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

• Calyceal diverticula are 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 (4):
    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 seldom 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 kidney stone burden <1.5 cm in transplant kidneys; 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.
• 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.

Evaluation of Outcome

• Comparison of outcomes between endourologic stone treatment types is difficult due to varied 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
    • Success rate
      • 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