Urolithiasis is a commonly encountered clinical problem,
accounting for 7-10 hospital admissions per 1000 in the United States with similar figures reported for the United Kingdom. The main aim of treatment is complete stone clearance however the evolution and refinement of minimally invasive techniques has revolutionized the treatment of urinary tract calculi over the last three decades. The technique of Percutaneous Nephrolithotripsy (PNL) was first described in 1976 by Fernstrom and Johansson [1]. The technique has subsequently been refined,
rendering it an effective and safe treatment in the management of urinary tract calculi. Despite similar advances in endourologic techniques and extracorporeal shock wave lithotripsy (ESWL),
the role of PNL has expanded greatly,
due to a combination of technologic advances and patient factors and is now considered the treatment modality of choice for stones greater than 2cm in diameter.
Indications:
These can be broadly divided into two categories: factors relating to the stone and patient-related factors.
- Factors relating to the stone
Stone Size:
- Stone size or “burden” is closely related to stone-free rates and is therefore an important determinant of treatment modality
- Guidelines of the European Association of Urology recommend the use of PNL as the primary treatment modality for all stones greater than 2cm in diameter [2]
Staghorn calculi:
Fig.: Figure 1: Pre PNL radiograph demonstrating large staghorn calculus forming a cast of the entire renal pelvis and calyceal system on the right. The staghorn calculus was completely cleared with PCNL.
- Treatment of choice for patients with staghorn calculi
- American Urological Association (AUA) [3] found
Higher stone free rates for PNL compared to open surgery for staghorn calculi (78% v 71%)
Higher stone free rates for combined approach PNL & ESWL for staghorn calculi v ESWL alone
Lower number of mean procedures necessary for treatment when PNL was used either alone or in combination with ESWL than for ESWL or open surgery alone
- PNL associated with lower morbidity (16% v 37%) and shorter in-patient hospital stay (4 v 6 days) when compared with open surgery for the treatment of staghorn calculi [4]
Stone Location:
- PNL is the treatment modality of choice for lower pole calyceal stones
- Stone free rates have been shown to be higher for lower pole calyx stones >1cm treated with PNL v ESWL (85-90% v 50-56%) in a number of retrospective studies [5,
6,
7]
- Randomized controlled trial has shown that stone free rates dropped as low as 21% for calculi >1cm treated with ESWL [8]
- Lower pole stones treated with PNL have a lower recurrence rate one year post treatment than those treated with ESWL (4% v 22%) [6]
- PNL may also be used for large calculi in the proximal ureter with higher reported stone free rates compared to ureteroscopy (95% v 58%) [9]
Stone composition:
- Renal calculi can be rendered highly resistant to fragmentation by their chemical composition
- Such calculi pose significant difficulty for treatment with ESWL.
Examples include either very hard (cystine,
calcium monohydrate,
brushite) or very soft stones (uric acid and matrix stones)
- Soft stones,
in addition to being resistant to fragmentation due to their putty-like consistency,
are radioloucent and thus difficult to target fluoroscopically at ESWL
- Struvite calculi result from chronic urinary tract infection (UTI) with urea-splitting organisms e.g.
Proteus and Klebsiella,
and due to the presence of foreign bodies in the urinary tract which become encrusted and act as a nidus for stone formation
- In such cases,
PNL provides the best treatment option for complete eradication of stone burden
Stones in patients with anomalies of the renal tract (congenital or acquired)
A number of congenital anomalies of the urinary tract are associated with impaired drainage and therefore a low probability of successful passage of stone fragments following ESWL
- Horseshoe kidneys
- Calyceal diverticula
Fig.: Figure 2: Control radiograph obtained during PNL demonstrates right retrograde ureteral catheter in situ. A 1.5cm cluster of tiny calculi is visualised overlying the upper pole of the right kidney, within a calyceal diverticulum.
Fig.: Figure 3: Opacification of the stone-bearing calyceal diverticulum and its communicating infundibulum (arrow) is achieved following injection of dilute contrast via the ureteral catheter. The diverticulum is then punctured under fluoroscopic guidance using an 18 Gauge Chiba needle.
- Ectopic kidneys
- Fused kidneys
- Transplant kidneys
Fig.: Figure 4: Control radiograph from PNL demonstrating surgical clips overlying the right iliac fossa from prior renal transplant. A 1.5cm radiopaque calculus is present within a lower pole calyx.
Fig.: Figure 5: Successful puncture of the lower pole of the right iliac fossa transplant was achieved using an 18G Chiba needle. Dilute contrast was then injected to opacify the ureter and bladder.
- Stones in obstructed systems requiring simultaneous correction e.g.
pelviureteric obstruction (PUJO)
Fig.: Figure 6: Retrograde catheter in situ which has been used to opacify the collecting system, demonstrating typical PUJ obstruction configuration. Multiple small calculi are identified in the lower pole and interpolar calyces.
2.
Factors relating to the patient
Urinary diversion:
- Approximately 10% of ileal conduits are associated with the development of calculi
- Retrograde access is typically challenging for the urologist and stone clearance rates of up to 100% are reported for this patient subgroup when treated with PNL [10]
Fig.: Figure 7: Spot fluoroscopic image from a PNL procedure demonstrating tip of 30 French sheath (small arrow) in the renal pelvis with an internal/external ureteral stent in situ with its distal tip in the ileal conduit (large arrow).
Skeletal malformations:
- May be a suitable alternative in patients with severe scoliosis,
contractures or spina bifida in whom treatment with ESWL is not feasible due to limitations posed by ineffective coupling with the shockwave head
Obesity:
- Increasing trends towards patient obesity in Western populations imposes significant limitations on the use of ESWL e.g.
imaging resolution,
weight limit for fluoroscopy table. In addition,
increased “skin to stone” distance limits the effectiveness of ESWL with success rates as low as 57% reported [11]
- Surprisingly,
many studies have shown that BMI does not affect PNL in terms of duration of hospital stay and complications with similar stone free rates reported as with non-obese populations [12]
Occupation:
- The diagnosis of renal tract calculi in some professions such as commercial and military pilots,
even if asymptomatic,
results in immediate cessation of flight duties until treated
- Several centres have found PNL to minimize the work-time lost and result in the highest rates of stone clearance [13]
Contraindications:
Few absolute contraindications to PNL exist. These include:
- Untreated coagulopathy
- Hydatid cyst
Relative contraindications include:
- Pregnancy
- Concurrent urosepsis
- Non-functioning kidney
- Anaesthetic co-morbidity
- Lack of safe percutaneous access e.g.
overlying colon
Principles of PNL access:
Aims:
- The aim of PNL is to produce complete stone clearance
If complete clearance is not technically feasible
- Clear the renal pelvis to improve drainage
- Clear the stone burden from the lower pole calyces preferentially,
as these are less likely to respond to ESWL
- Calculi remaining in the upper or interpolar calyces can later be treated with ESWL
Access:
- Anterior calyces can be accessed via a posterior calyx puncture
- Anterior calyceal entry makes intrarenal navigation more difficult
- Upper pole access while associated with a higher rate of vascular and pleural injury,
allows access to the pelvi-ureteric juction and upper ureter
The fornix is the ideal puncture site for PNL access. The risk of vessel dilation associated with 30 Fr dilation is [14]:
- <8% venous injury,
0% arterial injury for fornix
- 33% for renal pelvis
- 38% for interpolar infundibulum
- 68% for both the upper and lower infundibulum
Interpolar access
- This requires greater torque forces to reach the upper and lower poles and is associated with 3.5 times the rate of complications
- Should be used selectively for specific indications e.g.
stone-bearing calyceal diverticula & staghorn calculi
Supracostal access
- Use ultrasound to mark the lung,
liver/spleen prior to puncture
- Avoid the paraspinal muscle
- Reduce the tidal volume to move the aerated lung out of the access field
Dilation:
Dilation should be performed only as far as the fornix
Fig.: Figure 8: Spot fluoroscopic image demonstrating balloon dilatation being performed beyond the fornix.
Fig.: Figure 9: Balloon dilatation is optimal in this case, being performed just as far as the fornix.
Care should be taken not to over-advance the sheath and advancement should therefore be performed under fluoroscopic guidance
There should be a low threshold for insertion of a second tract if the first is sub-optimal