Ureteral Calculi


Investigator

Year

Procedure

Instrument

Young

1929

Ureteroscopy for dilated ureter in infant with Puv

Pediatric cystoscope

Marshall

1964

Diagnostic ureteroscopy
 
Goodman

1977

Therapeutic ureteroscopy—fulguration of ureteral tumor

Pediatric cystoscope

Raney

1978

Electrohydraulic ureterolithotripsy
 
Das

1981

Ureteral basket stone removal under direct vision

Pediatric cystoscope  +  basket

Dretler, Watson, Parrish & Murray

1987

Ureteroscopy  +  laser lithotripsy

Pulsed dye laser

Dretler & Cho

1989

Modern-day ureteroscopy

Semirigid ureteroscope





Natural History of Ureteral Calculi


Stone factors including size and location influence the rate of spontaneous passage, without any intervention. The majority of small ureteral calculi will pass spontaneously if given sufficient time. For stones less than 4 mm in diameter, two-thirds pass spontaneously within 4 weeks of symptom onset with an average time for passage being 1.6 weeks, compared with 2.8 weeks for stones 4–6 mm [14]. The current combined AUA/EAU guidelines on ureteral calculi report an estimated spontaneous passage rate of 68% (95% CI: 46–85%) for stones ≤5 mm [15]. For stones >5 mm and ≤10 mm, the estimated spontaneous passage is 47% (95% CI: 36–59%).

In the absence of ureteral disease, the width of the stone is the most significant measurement affecting the likelihood of stone passage [16]. As such, a linear association is seen between stone size and spontaneous passage rates, with rates of 87, 72, 47, and 27% for stones measuring 1, 4, 7, and 10 mm, respectively [17]. The systematic review by Hübner and colleagues showed a similar relationship between stone size and passage rates from a pooled analysis of 6 studies totaling 2,704 patients [14]. The rate of spontaneous passage for stones smaller than 4 mm was 38% compared to 1.2% for those larger than 6 mm within 4 weeks, irrespective of their position in the ureter at the time of presentation. Another systematic review of 37 pooled studies showed that in symptomatic ureteral calculi <4 mm, 38–71% will pass spontaneously and only 4.8% of stones <2 mm will need intervention during surveillance [7].

Stone location also influences clearance rates and has associated passage and impaction rates, i.e., proximal calculi pass less spontaneously than distal calculi, when controlled for size. Early studies showed a passage rate of 71% for distal calculi, and only 22% for proximal calculi, with an overall passage rate of 60% [18]. Other similar studies indicated less impressive results: calculi discovered in the distal third of the ureter had a spontaneous passage rate of 45%, compared with the mid third at 22%, and the proximal third at 12% [14]. Furthermore, the advent of medical expulsive therapy (MET) has improved the rate of spontaneous passage rates. Pooled results of high-quality randomized controlled trials in a contemporary meta-analysis showed a 65% greater likelihood of spontaneous stone passage with calcium channel blockers or alpha-blockers, compared to patients not receiving these drugs [19].

Some of the differences in reported stone passage rates can be attributed to measuring stone-free rates (SFRs). It should be kept in mind that the time needed for spontaneous clearance to occur can vary between patients and is not always apparent in the reporting criteria of studies; as such, an adequate period of observation is necessary if this is the chosen initial approach. The variability of observed spontaneous stone passage rates may be influenced by the duration of observation given before intervention is chosen, individual patient characteristics, and other confounding factors such as stone location or the use of MET. Furthermore, it has been shown that the criteria chosen to measure stone size can have interobserver differences [20]. However, cumulative results of studies indicate that 38–100% of stones <5 mm can be expected to pass spontaneously within 4 weeks. Thus, if spontaneous passage is chosen, the advantages of this approach must be weighed against the potential benefits of early definitive intervention. In general, literature supports that if significant progress has not occurred within 40 days of observation, intervention is necessary [18, 21].


Predictors of Spontaneous Passage


Interestingly, a recent study looking at the various factors influencing stone passage implicated serum WBC count as having a predictive potential for spontaneous passage. This study showed that its value, at the acute phase of a renal colic, is a significant predictor for stone spontaneous passage and should be considered [22]. The rationale for this observation is that a more mobile stone might cause more micro-trauma to the ureteral epithelium, causing a relatively more pronounced inflammatory response. However, the clinical utility of this is yet to be determined; even if a higher WBC count may suggest a greater likelihood for the stone to pass, it should be cautiously weighed against the possibility of an underlying infection or sepsis. Other potential predictors included stone sidedness, with a higher likelihood for left-sided stones to pass.


Ureteroscopic Treatment of Ureteral Stones



Ureteroscopy Versus Shock Wave Lithotripsy


The options for management of ureteral stones include conservative approaches such as active monitoring, and MET, minimally invasive procedures such as shock wave lithotripsy (SWL) and URS, and less often, laparoscopic ureterolithotomy. Taking together the observed rates of spontaneous stone passage, and variable time frame with which stones pass, the timing of when and modality with which to intervene can be challenging. Several factors, including patient preference, stone burden and location, resource availability, and surgeon skill, all contribute to the chosen treatment approach. Although conservative approaches such as observation or MET are acceptable options, passage of stones with such approaches may take several weeks to occur, during which period, patients may remain symptomatic, requiring ER visits, hospital admission, and analgesic use. Interestingly, despite its proven role in promoting stone passage, MET is still rarely used at the primary care level [19, 23]. In select cases, it might be prudent to offer early definitive therapy after a thorough discussion with the patient.

The indications and recommendations for URS have changed over the years, and is largely attributable to the refinement of flexible and rigid ureteroscopes, improved optics and ancillary instruments such as laser fibers and baskets, and to an extent evolution of surgical technique. Also, SWL has proven to be less effective than once thought. The updated ureteral stone guidelines reflect these changes, with an expansion for the indications of URS in treating ureteral stones [6]. While no differences in overall SFR were found between SWL and URS, the only instance in which SWL yielded slightly higher SFR was for proximal ureteral stones ≤10 mm. URS had significantly higher SFR for proximal stones >10 mm and for distal ureteral stones of all sizes. For all mid-ureteral stones, URS trended towards superior results but did not reach statistical significance. Such outcomes data would indicate that URS is perhaps less affected by stone burden than is SWL [24], and for obvious reasons, i.e., with SWL, the larger the stone burden, the more fragments that need to pass. URS is now deemed appropriate as first-line therapy for stones of any size in the proximal ureter, with clear benefits for stones >10 mm. Consistent with this is the updated Cochrane review comparing SWL to ureteroscopic management of ureteral calculi, which evaluated data from 7 randomized controlled trials. The authors report lower SFR (RR 0.84) and higher retreatment rates (RR 6.18) with SWL compared to URS, but with the benefit of shorter hospital stay and fewer complications (RR 0.43) [25]. This was further illustrated by Raman et al., where the number of primary procedures (i.e., the intended treatment modality) was fewer for URS compared to SWL at all ureteral locations, indicating a higher retreatment rate for SWL [24]. Scales and colleagues showed in a recent analysis that the odds of a second procedure following initial SWL were 1.54 times those of URS [26]. In their review, they showed that in beneficiaries undergoing initial SWL, 38% underwent an additional procedure within 120 days, versus 9% for URS and 18% for URS plus holmium laser.

Although the 1997 ureteral stone guidelines recommended SWL for stones <10 mm and either SWL or URS for stones >10 mm in the proximal ureter, the current guidelines, along with more recent data, reflect a change in this assertion. This shift in outcomes is largely due to improved endoscopic technology as discussed earlier, rendering URS easier and safer. Furthermore, newer devices such as the Stone Cone (Microvasive; Boston Scientific Corp., Spencer, IN) and N-Trap (Cook Urological, Spencer, IN) to prevent stone retropulsion during proximal URS may further contribute to the improved results [27, 28].

Unfortunately, it is very difficult to draw direct comparisons between available studies due to the variability in methodologies and criteria for determining SFRs; this continues to affect newer literature as well, as outlined in the Cochrane review discussed above. The limitations in assessing the currently available literature on SWL and URS stem from the lack of standardization in comparing stone size and burden, and more universal criteria in future study designs might permit a more accurate standard of comparison [20].


Current Trends in Treatment of Ureteral Calculi


In a recent review of over 9,000 beneficiaries in the USA who underwent an initial procedure for the treatment of ureteral stones, several patients, providers, and practice setting characteristics were associated with the selection of URS versus SWL [26]. As might be expected, the odds of undergoing URS was 44% higher when treated at a high-volume URS facility versus 68% lower odds when treated at a high-volume SWL facility. A significant and interesting finding in this review was that female patients were less likely than males to undergo URS. Such gender-based preferences for the treatment modality for ureteral stones may have subtle clinical implications, in light of the observed trend of higher rate of increase in the incidence of stone disease in women compared to men. Congruent with these findings was a study that showed more recently that trained urologists were more likely to use URS than SWL, based on an analysis of board certification logs [29]. Leijte et al. showed that surgeon experience was indeed a predictive factor for complications and success for ureteroscopic holmium laser lithotripsy for ureteric calculi. Experienced surgeons had fewer complications, and the success rate was higher [30]. Nonetheless, current practice patterns indicate a consistent trend among American urologists towards URS and away from SWL for the management of stones of all sizes throughout the ureter [31]. For example, even with an expansion of extracorporeal lithotripter ownership in the state of Michigan, an associated drop in the rate of URS was not seen [32].

A cost–benefit analysis showed that, after failed observation, URS is the most cost-effective treatment strategy for ureteral stones at all locations [33]. Although observation alone is purported to be more cost-effective than surgical treatment, costs of total observation are more difficult to ascertain as the observation regimen is less controlled due to variations in management, with variable hospital ER visits, loss of work secondary to pain, etc. Cumulative economic data suggest that URS is the most cost-effective treatment strategy for ureteral stones in all locations, after observation fails [34].


Stone Factors



Size and Location


The probability of spontaneous stone passage as discussed previously is directly correlated with the distance of ureter to be traversed and inversely with that of stone size. Greater ureteroscopic success is observed as the stone location is more distal, and as the stone burden is lower. It is known that ureteral stones are held up at predictable sites: the UPJ, crossing of the ureter over the iliac vessels, and at the UVJ, the narrowest portion of the ureter. However, recent clinical studies demonstrate the two most common sites of stones to lodge in patients presenting to the ER with renal colic: the UVJ (60.6% of cases), and the proximal ureter between the UPJ and the iliac vessels (23.4%) [35]. In this study, the proportion of stones lodged at the UPJ and crossing of the iliac were only 10.6 and 1.1%, respectively. These findings would indicate a greater role for URS over SWL, based on the previous outcomes discussion.

The technical challenge of treating proximal stones is greater than distal stones, potentially contributing to the lower SFRs at these locations. This is due to the instrumentation distance required to traverse and access the relatively more delicate upper ureter and added challenges due to stone migration during treatment. However, with the advent of newer and more sophisticated equipment, the gap in the SFRs between proximal and distal stones is decreasing [34]. Hollenbeck et al. showed that endoscopic management of proximal ureteral stones is highly successful, without an increase in complication rates, and that the differences in success rates between proximal and distal calculi have narrowed substantially [36].

The current ureteral stone guidelines report SFRs of 81, 86, and 94% for ureteroscopic management of proximal, mid, and distal ureteral calculi, respectively [15]. In comparing SWL versus URS in this report, the SFRs were 82 vs. 81%, respectively, for proximal ureteral calculi, 73 vs. 86% for middle ureteral calculi, and 74 vs. 94% for distal ureteral calculi [15]. Ureteroscopic SFRs showed less size dependence with comparable rates for proximal, middle, and distal stones ≤10 mm and >10 mm. Newer series report SFRs of 72, 95, and 99% [37] and 80, 94, and 91% [38], for proximal, mid, and distal calculi, respectively. It is important to note, however, that in some contemporary series, lower SFRs were observed for proximal stones, such as 69.4 [39] and 59% [40]. Another recent series showed SFRs of 77, 85, and 91%, but subgroup analysis for stones >10 mm showed that the SFRs were 54, 77, and 88%, respectively [41]. Table 7.2 highlights ureteroscopic outcomes from selected recent series since the 2007 guidelines for stones at various locations in the ureter.


Table 7.2
Ureterolithotripsy outcomes: Selected contemporary series (after 2007 guidelines review)







































































































     
Mean stone size (Mm)

Overall % SFR (# patients)

SFR (days, modality)
 

Investigators, year

Study type

Total # patients

Distal

Mid

Proximal

I nstrument used

Al-Ghazo et al. 2011

Retrospective

244
 
96.6%

95.8%

69.4%

4 weeks, Kub

7.5, 8f Semirigid; Swiss Lithoclast

Best And Nakada 2011

Retrospective

43

9.1

N/A

N/A

86%
 
Flexible; Ho:Yag Laser

Ciftci et al. 2010

Retrospective

336

9.77

90.7%

85.5%

76.5%

4 weeks, Kub

9.5f Rigid; Pneumolithotripsy

Hong and Park 2009

Retrospective

341

8.8 (D)

96.9%

93.8%

80.3%

2 weeks, Kub

9.5f, 10f Rigid; Swiss Lithoclast

8.7 (M)

10.9 (P)

Yencilek et al. 2010

Retrospective

1,416

12.1

98.9%

94.8%

71.7%
 
Semirigid; Pneumatic Lithotripsy

Ather et al. 2010

Retrospective

265

>30 mm2

92%

53%

59%

3 months

6.4, 7, or 8 F Semirigid; Swiss Lithoclast

Preminger et al. 2007

Systematic Review—2007 Aua Guidelines

8,194

N/A

94%

86%

81%

N/A

N/A

In all, given the excellent overall results with URS, the guidelines on ureteral calculi now recommend URS to be appropriate for stones of any size and in any location in the ureter. This meta-analysis demonstrated that the URS yields significantly greater SFR for the majority of stone stratifications.


Stone Composition


Stone composition dramatically affects SWL efficacy, whereas URS is less affected by stone type. It is established that SWL is not as effective for cystine, brushite, or calcium oxalate monohydrate stones [42]. In contrast, studies evaluating the success rates of Holmium laser lithotripsy have shown equal efficacy for most stone types, including calcium oxalate monohydrate stones [43]. This study further demonstrated that radio-opacity of the stone has no bearing on laser lithotripsy. Teichman’s review of his earlier studies showed that the holmium-YAG laser is effective for stones of all composition and sizes [42].


Very Large/Impacted Proximal Ureteral Stones


In cases with impacted stones in the proximal ureter, URS can be technically more challenging. As discussed above, URS yields better SFRs than SWL for proximal ureteral stones larger than 10 mm. Even in centers where flexible ureteroscopes are not available for example, semirigid URS is efficacious for proximal ureteral stones >10 mm, with excellent SFRs and safety profile [44]. This begs the question of a recommended maximum stone size for URS, i.e., in stones larger than 20 mm. Chen et al. showed that proximal ureteral stones >20 mm can be safely treated with semirigid URS and Holmium:YAG laser lithotripsy while achieving excellent SFR (84% at 4 weeks post treatment); here, no complications were reported [45]. In situations where traditional URS may not seem feasible or appropriate for proximal stones, i.e., for a stone that is too large or severely impacted, an antegrade approach may be suitable, which is discussed next.


Antegrade Ureteroscopy for Proximal Impacted Stones


The treatment of larger or impacted proximal stones can be challenging, with the attendant risk of ureteral perforation and higher likelihood of stone migration during fragmentation. Antegrade URS has been described for impacted proximal and mid ureteral stones dating back to 1989 [46]. The AUA guidelines state that percutaneous antegrade URS is an acceptable first-line treatment in select cases [15]. As such, this, along with other studies, speaks to the feasibility and safety of this technique, in view of evolving technology [47, 48]. Retrospective series comparing antegrade with retrograde URS for impacted large upper ureteral calculi showed that better SFRs were achieved with the antegrade approach, and without complications [49]. A recent study prospectively looked at the utility of antegrade URS, where patients with large (>10 mm), impacted proximal ureteral calculi were randomized to either the standard retrograde URS or an antegrade approach [50]. This was based on a “mini-PCNL” technique for the antegrade group, with the access tract dilated to 16 F and utilization of a sheath that extended to the UPJ. Their results were in favor of the antegrade procedure, with SFR at discharge home being 95.3 vs. 79.5% for the retrograde group. It is to be noted, however, that the hospital stay was longer in the antegrade group (6.3 days vs. 2.1 days), although the complication rate was similar in both groups. Conversely, a randomized study comparing retrograde, antegrade, and laparoscopic approaches for proximal stones >15 mm failed to show any significant differences in stone clearance or an obvious benefit for one over the others [48].

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Sep 21, 2016 | Posted by in UROLOGY | Comments Off on Ureteral Calculi

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