Current Trends in the Treatment of Ureteral Stones

Introduction

Ureteral calculi are one of the most common urological problems encountered by urologists nowadays. Timely and systematic treatment can bring about a successful outcome whereas late and inappropriate treatments can lead to unnecessary suffering and significant complications including deterioration of renal function.

Current Modalities of Treatment

Currently, ureteral stones can be treated by various modalities depending on different situations.

Medical Expulsive Therapy (MET)
Extracorporeal Shockwave Lithotripsy (ESWL)
Ureteroscopic lithotripsy (URSL)
Percutaneous Nephrolitotomy (PCNL)
Laparoscopic or robotic-assisted Laparoscopic surgery
Open surgery (where facilities and expertise are not available)

Determining the optimal treatment for a given patient is not always straightforward. It depends on stone-related factors, clinical factors, and technical factors .It is the interplay of these factors and the familiarity of the urologist with each surgical technique that ultimately determine the best treatment modality for a given patient.

The purpose of this article is to provide a sound knowledge and to provide a framework to help guide urologists in matching a given patient’s unique clinical situation and ureteral stone disease characteristics to the most effective and least morbid surgical therapy.

Natural History

When a renal calculus begins to pass, it moves from the kidney into the ureteropelvic junction (UPJ) and into the ureter proper. At that point, depending on the size of the stone relative to the ureter throughout its course, the stone will begin to obstruct the kidney. The first manifestation of this is an increase in the intra–collecting system pressure, which will stretch the renal pelvis, calyces, and renal capsule. It is during this phase that the traditional colic of a stone episode will begin.

This increase in intraluminal pressure will increase the hydrostatic pressure exerted on the walls of the renal pelvis and ureter, which can cause the failure of normal peristalsis. Pressure further increases at that point, with direct transmission to the nephron tubules, with a resulting drop in the glomerular filtration rate (GFR).

Pressure will subsequently decrease to the levels that were present before obstruction developed, usually within 12 to 24 hours. Accordingly, the renal colic episode caused by a stone is often limited to severe pain from the acute renal stretch, followed by gradual resolution of the pain.¹

Further movement of the stone down the ureter can relieve the pressure and reobstruct further distally, explaining the intermittent nature of renal colic as a stone passes.

Long-term obstruction can cause permanent damage to the kidney’s function; therefore, regardless of the absence of pain or infection, a stone must either pass spontaneously or be surgically treated. Key to the passage of a stone is ureteral peristalsis, not hydrostatic pressure.²

When the ureter is not otherwise obstructed, the chief determinant of stone passage is the diameter of the stone in its transverse orientation. Next most important is the location of the stone within the ureter at presentation, with a review of the literature demonstrating a 71% chance of passage of a distal ureteral stone versus 22% for proximal stones.³

Additional evidence supports the idea that the likelihood of spontaneous passage may be directly related to stone location at the time of presentation.^1,4

With respect to size as a predictor of spontaneous passage, meta-analysis of the available literature demonstrates a 68% chance of passage for stones 5 mm or smaller, and an estimated 47% chance for stones 6 to 10 mm in size.⁵

These rates can be enhanced with medical expulsive therapy (MET) using either αlpha-receptor blockers or calcium channel blockers. Alpha Blockers (Tamsulosin, Doxazocin, Terazocin) appeared to offer an overall greater increase of spontaneous passage, with an absolute increase in chances of passage calculated at 29% across all stones.

Thus, for ureteral calculi 5 mm or smaller, MET with expectant management is a reasonable therapeutic choice. Please be reminded that these patients can have postural hypotension and retrograde ejaculation due to the side-effect of alpha- blockers.

Pretreatment Assessment and urgency of treatment

The pretreatment assessment, including medical history, imaging, and laboratory testing, for ureteral stones include KUB and Trans abdominal Ultrasound as a conventional way. If clinical assessment is certain to be ureteral stone, we can go straight to CT KUB which is very helpful for decision making of the best treatment modality.

Particular attention should be directed toward the duration of symptoms, given the fact that long-term obstruction can result in irreversible nephron loss.

If there is fever in the setting of a ureteral stone with hydronephrosis, it strongly suggests the presence of infection proximal to the point of obstruction.

Appropriate broad spectrum antibiotics must be started parenterally and emergency drainage of infected and obstructed upper tract by either Percutaneous Nephrostomy or Ureteroscopic Double J stent insertion must be done in all the centers where facilities and expertise are available.

After a period of about two weeks when infection is sorted out, we can do definitive intervention for stone removal.

Specific symptoms may give clues to the course of the episode: New-onset urgency and frequency may herald 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.

Assessment of renal function is paramount because ureteral stones are often obstructing at the time of presentation, and therefore renal function may be impaired. Please remember, serum creatinine will not rise due to obstruction of one upper urinary tract. In other words, normal range creatinine does not exclude significant obstruction of one upper urinary tract by ureteral stone.

Treatment of Ureteral Stones

Treatment of Ureteral Stones is decided based on Stone-related factors such as

Stone location
Stone Size and
Stone Composition together with factors like degree of obstruction, symptom severity, patient’s expectations, associated infections, available equipment & expertise and Cost.

Stone location & size

Stones at Proximal and Mid-Ureter. The chief determinant of the optimal treatment for calculi in these locations is size. As previously mentioned, those which are more proximal and greater in size are significantly less likely to pass spontaneously. There is a paucity of data on the effectiveness of MET use in proximal and mid-ureteral stones, although since many of these stones do migrate distally, presumptive use of MET is not contraindicated.^6,7

For stones that do not move in a reasonable time frame, or in the setting of recurring severe pain, or if the patient prefers, surgical therapy is indicated. Primary options include ESWL (Fig.1) and URSL (Fig. 2), although PCNL (Fig. 3) may be indicated for selected cases. Pooled data, as evaluated in the AUA ureteral stone guidelines, have defined outcomes in proximal and mid-ureteral stones (of all sizes) in patients who underwent ESWL, with overall 82% and 73% treatment success rates, respectively.5 When considering proximal ureteral stones that are 1 cm or smaller, ESWL success rises among these pooled series to 90% (85% to 93%), and 84% (65% to 95%) for mid-ureteral stones. For stones larger than 1 cm, rates of complete stone clearance drop in both groups, to 68% for proximal and 76% for mid-ureter stones.

Similarly, the guidelines pooled numerous studies to evaluate outcome success for URSL for these locations and sizes, demonstrating an overall success of 81% for proximal and 86% for mid-ureteral stones.⁵ Calculi 1 cm or smaller again demonstrated higher success rates in both groups than did larger stones.

The cost-efficiency of management of proximal ureteral stones has been shown to be superior for URSL when compared with ESWL, when used as the initial treatment procedure.⁸

For very large proximal ureteral calculi not amenable to either ESWL or URSL, Percutaneous Nephrolithotomy (PCNL) is the best treatment option. Lastly, laparoscopic Ureterolithotomy (Fig 4) and robotic assisted laparoscopic Ureterolithotomy (Fig 5) have been described for LARGE proximal and mid-ureteral calculi, which are not suitable for URSL or PCNL, with success rates for stone clearance in selected cases of 93% to 100%. Significant discussion regarding such an approach, in many cases significantly more invasive than ESWL, URSL, or PCNL, should be undertaken with the patient when considering this option.

It is important to note that stones in a mid-ureteral location are typically handled in much the same way as proximal calculi, although some considerations relative to the pelvic anatomy will apply. With respect to ESWL, the presence of the bony structures lying posterior to the ureter at this level can interfere with fluoroscopic or plain film imaging of the stone, as well as pose challenges to positioning the patient so that shock wave energy does not pass through the bone. Oblique or prone positioning may be required for ESWL at this level.

Finally, URSL for the mid-ureteral stone can often be accomplished with a semirigid ureteroscope; however, limitations caused by the iliac vessels, particularly in male patients, may be encountered. In addition, proximal migration of these stones can some- times present a challenge with semirigid instrumentation. The availability of flexible ureteroscopes and the skills to perform flexible URSL will improve the overall success rates and decrease complications.

Stones at Distal Ureter

As discussed earlier, distal stones are most likely to pass with observation or Medical Expulsive Therapy(MET).⁵

The most typical site for impaction in this region of the ureter is at the Vesico-ureteric Junction (UVJ); stones reaching this location often cause significant irritative symptoms owing to stimulation of the bladder, a clinical sign that helps localize them. When stones fail to pass, once again surgical therapy is indicated.

ESWL and URSL both remain the mainstays of treatment of distal ureteral stones. Once again, the AUA ureteral stone guidelines present a detailed review of pooled studies to identify success rates in both procedures. Among reviewed series using ESWL for distal ureteral stones, the overall success rate was 74%. When considering stones 1 cm or smaller, an overall success rate of 86% was noted, whereas stones larger than 1 cm yielded a success rate of 74%.5 In the same ureteral calculi guidelines analysis, URS for the distal ureteral calculus was shown to yield a 94% overall success rate, with stones 1 cm or smaller at 97% and over 1 cm at 93% success rate.

All Locations

Additional factors to consider in addition to stone- free success rates in the choice of therapy include the following:

The complications of therapy such as sepsis, steinstrasse, ureteral stricture, and ureteral injury
Anesthetic requirements
Bleeding risk in patients with anticoagulation or antiplatelet
Therapy
Recovery expectations
Potential need for adjunctive procedures

Treatment decision by Stone Burden

As described earlier, ESWL success for ureteral stones at all locations is significantly affected by the total stone burden, just as it is for renal calculi: The larger the stone, the less effective the treatment5. As a specific example, the success rates for SWL at the distal ureter were 86% for stones 1 cm or smaller and 74% for those larger than 1 cm, and such differences held true for all locations. In contrast, URSL had a much smaller degree of variation in terms of success based on stone burden: 97% success for stones 1 cm or smaller and 93% for those larger than 1 cm.

In a cost-comparison study of the management of ureteral calculi, Lotan and colleagues demonstrated that URSL was associated with a lower cost than SWL for proximal stones, even before factoring in the higher adjunctive procedure rate associated with ESWL.8

Treatment decision by Stone Composition

Assessment of ureteral stone density based on the Hounsfield units on CT scan can offer valuable predictive ability as to the stone-free rate using ESWL. Stone density varies depending on different types of stones. Stones with density of less than 900 are more suitable to be treated with ESWL.

Therefore, whenever possible, it is best to obtain prior stone composition data or prediction of composition based on radiological studies, so as to best inform the patient regarding choices of therapy and possible outcome.

Conclusion

It should be clear that it is imperative to tailor therapy choices to the individual patient, after careful discussion of outcomes of treatment: success rates, adjunctive procedures, and treatment-related morbidity. Both patient factors (body habitus, coagulation status, medical comorbidities) and stone factors (location, burden, composition) must be considered when selecting the optimal treatment for ureteral calculi.

References

Hubner WA, Irby P, Stoller ML. 1993. “Natural history and current concepts for the treatment of small ureteral calculi.” Eur Urol 24:172–6.
Lennon GM, Thornhill JA, Grainger R, et al. 1997. “Double pigtail ureteric stent versus percutaneous nephrostomy: effects on stone transit and ureteric motility”. Eur Urol 31(1):24–9.
Morse RM, Resnick MI. 1991. “Ureteral calculi: natural history and treatment in an era of advanced technology”. J Urol; 145:263–5.
Coll DM, Varanelli MJ, Smith RC, et al. 2002. “Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT”. AJR Am J Roentgenol; 178:101–3.
Preminger GM, Tiselius HG, Assimos DG, et al. 2007. “Guideline for the management of ureteral calculi.” J Urol; 178:2418–34.
Hollingsworth JM, Rogers MA, Kaufman SR, et al. 2006. “Medical therapy to facilitate urinary stone passage: a meta-analysis.” Lancet;368(9542): 1171–9.
Seitz C, Martini T, Berner L, et al. 2008. “Efficacy and treatment outcome of a new electromagnetic lithotripter for upper urinary tract calculi.” J Endourol;22(11):2519–25.
Lotan Y, Gettman MT, Roehrborn CG, et al. 2002. “Management of ureteral calculi: a cost comparison and decision-making analysis”. J Urol;167: 1621–9.