Shock Wave Lithotripsy for Kidney Stones
Shock wave lithotripsy uses focused energy generated outside the body to break selected kidney and ureteric stones into smaller fragments that can then pass through the urinary tract.
CT imaging helps assess size, position, density and anatomy before treatment is selected.
Fever with an obstructed kidney stone requires urgent assessment
Shock wave treatment is not the priority when a patient has an infected obstructed urinary system. Fever, chills, significant illness, confusion, worsening symptoms or difficulty passing urine should prompt urgent medical assessment rather than waiting for routine stone treatment.
Learn about blocked or infected kidney stones →What is shock wave lithotripsy?
Shock wave lithotripsy—usually abbreviated to SWL and historically called extracorporeal shock wave lithotripsy or ESWL—treats a stone without passing a telescope through the urinary tract and without making a surgical incision.
A lithotripsy machine generates shock waves outside the body. Imaging is used to locate the stone and the energy is focused onto it. Repeated shock waves can progressively fragment a suitable stone into smaller pieces.
Treatment does not physically remove every fragment during the procedure. The fragments generally need to leave the kidney and pass through the ureter afterwards. This is one reason why the position of the stone and the anatomy around it matter when deciding whether SWL is likely to work well.
Which kidney stones are best suited to shock wave treatment?
SWL works particularly well when the stone can be accurately targeted, fragmented effectively and the resulting pieces have a reasonable pathway out of the kidney.
Stone Size
Smaller stone burdens are generally more favourable. As stone size increases, the chance of requiring repeat SWL or an alternative procedure also increases.
Stone Location
Stones in the renal pelvis, upper kidney or selected parts of the ureter may be favourable. Lower-pole kidney stones can be more difficult because fragments must leave the dependent lower calyx.
Stone Density
CT density provides information about stone hardness. Stones above approximately 1,000 Hounsfield units are generally less likely to fragment successfully with SWL.
Understand Hounsfield units →Kidney Anatomy
Calyceal anatomy, drainage angles and the route fragments need to travel can influence whether successful fragmentation ultimately results in stone clearance.
Ability to Target the Stone
The stone needs to be reliably localised during treatment. Visibility and the distance between the skin and stone can affect treatment effectiveness.
Stone Composition
Different stone types fragment differently. Some particularly hard stones are less responsive to shock waves and may be more suitable for an endoscopic approach.
Your CT scan can help predict whether SWL is likely to work
A CT scan provides considerably more information than simply stating that a kidney stone is present. It can help determine whether SWL is technically attractive or whether another treatment is more likely to achieve clearance.
What about a lower-pole kidney stone?
A stone in the lower part of the kidney can sometimes fragment successfully but still fail to clear completely.
This is because the resulting stone fragments need to travel out of the lower calyx and into the renal pelvis before entering the ureter. The anatomy of this pathway may work against gravity and reduce fragment clearance.
For lower-pole stones—particularly once they become larger—the relative advantages of SWL and flexible ureteroscopy deserve careful consideration.
Breaking the stone is not the same as clearing the stone.
The ideal treatment should consider both the likelihood that the stone can be fragmented and the likelihood that those fragments will successfully leave the kidney.
Explore ureteroscopy & laser surgery →How does shock wave lithotripsy work?
The details vary according to the lithotripsy system, stone location and individual treatment plan, but the overall process follows the same principles.
Locate the Stone
Imaging is used to identify the stone and position it within the treatment focus.
Position the Patient
The treatment head is coupled to the body so shock-wave energy can be transmitted efficiently toward the stone.
Deliver Shock Waves
Repeated focused shock waves are delivered. Energy may be progressively adjusted during the procedure.
Fragment the Stone
The aim is to reduce the stone into fragments that are small enough to subsequently pass through the urinary tract.
Pass the Fragments
Stone fragments may pass over the following days or weeks. Temporary renal colic can occur while fragments move.
Check Stone Clearance
Follow-up imaging may be recommended to determine whether fragments remain and whether further treatment is needed.
What happens after SWL?
Recovery is usually different from recovery after an endoscopic or percutaneous operation because there is no surgical incision and no ureteroscope has been passed to directly remove the stone.
However, the stone fragments still need to pass through the urinary tract afterwards. Symptoms therefore vary according to the amount of fragmented stone and how easily those fragments pass.
Temporary haematuria can occur following treatment.
Some soreness around the treated kidney region can occur.
Small fragments may pass in the urine over subsequent days.
Moving fragments can occasionally produce ureteric pain.
Will I need a ureteric stent with SWL?
Not routinely. One advantage of SWL for an appropriately selected stone is that a ureteric stent may not be required.
There are situations where a stent may nevertheless be appropriate, depending on the stone burden, obstruction, urinary anatomy, previous procedures and individual circumstances.
Learn about ureteric stents →SWL vs ureteroscopy vs PCNL
There is no universally “best” kidney stone procedure. The aim is to match the treatment to the stone rather than select a procedure in isolation.
| Shock Wave Lithotripsy | Ureteroscopy & Laser | PCNL | |
|---|---|---|---|
| Access | Energy delivered externally | Telescope through urinary tract | Direct tract through back into kidney |
| Skin incision | None | Usually none | Small percutaneous incision |
| Stone treatment | External fragmentation | Direct visual laser fragmentation / removal | Direct treatment and extraction |
| Often suited to | Selected smaller, targetable stones with favourable characteristics | Many ureteric and renal stones requiring endoscopic treatment | Larger or more complex renal stone burdens |
| Stone clearance | Relies on passage of fragments | Fragments can be removed and/or dusted | Allows direct extraction of larger stone burdens |
| Repeat treatment | Can be required | Can be required for larger stone burdens | May still require staged treatment for complex stones |
When might SWL not be the best option?
A treatment that is relatively non-invasive is not necessarily the treatment most likely to clear every stone.
Large Stone Burden
Larger stones may generate substantial fragments and have a greater likelihood of incomplete clearance or needing multiple treatments.
Very Dense Stone
High-density stones on CT can be relatively resistant to shock-wave fragmentation.
Unfavourable Lower-Pole Anatomy
Even when fragmentation occurs, fragments may remain within the lower part of the kidney.
Difficult Stone Targeting
Treatment effectiveness depends on being able to consistently localise and focus energy onto the stone.
Infected Obstruction
An infected obstructed kidney may need urgent drainage before definitive stone treatment is considered.
Need for More Predictable Clearance
In some circumstances direct endoscopic removal or PCNL may offer a more appropriate route to achieving stone clearance.
What are the possible risks of shock wave lithotripsy?
SWL avoids an incision but it is still a medical procedure and does not guarantee complete stone clearance.
Following fragmentation of a larger stone burden, multiple fragments can occasionally line up within the ureter and obstruct drainage. This appearance is sometimes called steinstrasse, or “stone street”. Further treatment may occasionally be required.
What if SWL has not completely cleared the stone?
Residual stone after SWL does not automatically mean that the same treatment should simply be repeated.
Updated imaging can show the amount of stone remaining, its location and whether the fragments are likely to clear spontaneously. The next step may be observation, further SWL, ureteroscopy or another treatment depending on the residual stone burden.
Explore residual kidney stones after treatment →How is the decision actually made?
Define the Stone
Size, location, number, density and urinary anatomy are reviewed.
Assess Its Impact
Symptoms, obstruction, infection, kidney function and previous treatment are considered.
Select the Treatment
Observation, SWL, ureteroscopy or PCNL can then be considered in the context of the individual stone.
Explore related kidney stone information
Shock Wave Lithotripsy FAQs
Common questions about selecting, undergoing and recovering from shock wave treatment for urinary stones.
Request a kidney stone assessment →Does shock wave lithotripsy involve surgery? +
SWL is a procedural treatment but does not normally require a surgical incision. Shock waves are generated outside the body and focused onto the stone.
Is SWL the same as ESWL? +
Yes. ESWL stands for extracorporeal shock wave lithotripsy. The shorter term SWL—shock wave lithotripsy—is now commonly used to describe the same treatment principle.
What size kidney stone can be treated with SWL? +
Size is important but is not the only determinant. SWL tends to be more attractive for smaller stone burdens, while selected stones up to around 20 mm may sometimes be considered depending on location, density and anatomy. Larger stone burdens are more likely to require another approach such as PCNL.
Why do Hounsfield units matter? +
Hounsfield units measure the density of a stone on CT. Higher density often indicates a harder stone. Stones above roughly 1,000 HU are generally less likely to fragment effectively with SWL.
Learn more about kidney stone density →Is SWL better than ureteroscopy? +
Neither treatment is universally better. SWL avoids passage of instruments into the ureter but relies on fragments subsequently passing. Ureteroscopy provides direct access to the stone and may offer a higher likelihood of clearance for some stones, although it is more invasive. The relative advantages depend on the individual stone.
Will the stone disappear immediately? +
Not necessarily. SWL fragments the stone rather than removing it intact. The pieces then need to leave the kidney and pass through the ureter. This can occur over days or weeks.
Can SWL fail? +
Yes. A stone may not fragment sufficiently, fragments may remain within the kidney, or further stone treatment may be required. Treatment success depends heavily on appropriate stone selection.
Can I need more than one SWL treatment? +
Yes. Repeat treatment is sometimes appropriate, although persistent stone after SWL may also be a reason to reconsider whether ureteroscopy or another approach is more suitable.
Does SWL require a ureteric stent? +
A stent is not routinely required before uncomplicated SWL in adults. It may nevertheless be used in selected circumstances based on stone burden, obstruction and individual clinical factors.
Can SWL be performed if I have a urine infection? +
Active urinary infection is an important consideration before stone treatment. Infection generally needs to be appropriately assessed and treated. An infected obstructed kidney may require urgent drainage rather than SWL.
What if I still have fragments after SWL? +
Follow-up imaging can determine their size and location. Some fragments can be observed while others may warrant additional treatment depending on symptoms, obstruction, infection risk and the amount of residual stone.
Learn about residual kidney stones →Can kidney stones return after successful SWL? +
Yes. Treating the current stone does not necessarily remove the underlying tendency to form stones. Recurrent stone formers may benefit from stone analysis, metabolic assessment and 24-hour urine testing.
Explore kidney stone prevention →Have you been told your kidney stone may be suitable for shock wave treatment?
Existing CT imaging can be reviewed to assess the stone's size, location, density and anatomy and determine whether SWL, ureteroscopy, observation or another treatment pathway is most appropriate.
This information is general educational information and does not replace individual medical advice. The appropriate treatment for a urinary stone depends on factors including stone size and location, stone density, symptoms, obstruction, infection, kidney function, urinary anatomy, previous treatment, medications and individual clinical circumstances. Patients with fever or significant illness associated with suspected urinary obstruction should seek urgent medical assessment.