Our site is fortunate that Dr. Luke Reynolds, an outstanding young urological surgeon, has created an article on percutaneous nephrolithotomy (PCNL). Many patients come to need this complex surgery, and most will not know much about it. An article about PCNL has long been missing and I am thrilled this talented and experienced surgeon has been willing to write it for us. Fred Coe
The lovely photograph of autumn’s gourds is by Phyllis Brodny, a contemporary artist to whose eyes these natural shapes display startlingly human attitudes. This image is from the cover of her book of gourds pantomiming life, the commonplace and the wonderful.
Origins of PCNL
Before the 1970’s patients suffering from kidney stones required open surgery. In 1976 Fernström and Johansson described a way to create a tract into the kidney through a small incision in the back. Instruments could be passed through the tract to remove stones. This was the first example of Percutaneous Nephrolithotomy (PCNL). PCNL has virtually replaced open surgery because it allows removal of even large stones.
Shockwave lithotripsy (SWL) and ureteroscopy (URS), perfected over the past decades, together with PCNL, make up the three main surgeries used for stone removal.
Why PCNL vs SWL or URS?
The straightforward answer is that large kidney stones (greater than 2 cm or 1 inch) are best treated by PCNL as URS and SWL often fail to remove all the stone material leaving behind residual fragments. Shockwave Lithotripsy (SWL) is ideal for one or perhaps a few smaller stones. Ureteroscopy (URS) can remove numerous stones but does poorly when the mass of stone is large. These are the general rules that surgeons tend to follow. Besides stone size and location, the anatomy of the kidney, symptoms, general health and patient expectations all weigh into the final decision.
This last is very important, as patients may well have their own priorities. SWL is the least invasive method and some may prefer it despite a greater chance of residual stone fragments. PCNL may be the ideal in a given situation but patients elect otherwise because the procedure is more invasive. URS stands somewhere in between these extremes. So a shared decision making process is needed between patients and their urologist to choose which treatment is truly right for them.
Benefits of PCNL
Most Likely To Make Kidneys Stone Free
Although PCNL is the most invasive treatment option for kidney stones, apart from the rare open surgery itself, it is the procedure most likely to clear the full stone burden in a single treatment. The American Urology Association guideline recommends, “In symptomatic patients with a total renal stone burden >20 mm, clinicians should offer PCNL as first line therapy”.
A randomized controlled study in 2015 (Karakoyunlu et al.) demonstrated that multiple URS sessions were needed in order to have a similar outcome to a single PCNL. Another finding of this study was that even with multiple treatments, patients still had a higher rate of small residual fragments with URS compared to PCNL. Residual stone fragments can be a problem in the future as they grow larger or cause pain, bleeding, infection, or obstruction.
Specially Good for Lower Pole Stones
Due to anatomy, stones in the lower pole of the kidney pose a particular challenge for surgeons. Fragments from SWL or even URS often lodge there, especially when the original stone was large. As an example, a randomized controlled trial demonstrated that PCNL produced a 95% stone free rate compared to 37% with SWL (Albala 2001).
A recent review article concerning treatment options for lower pole stones, confirmed that PCNL generally provides higher stone free rates compared to both URS and SWL. This is balanced, however, by a longer hospital stay and the potential for complications (Zhang 2015).
Given the trial data, the American Urology Association guidelines recommend, “Clinicians should inform patients with lower pole stones >10 mm in size that PCNL has a higher stone-free rate but greater morbidity”.
For any one patient, the final choice depends on anatomy and stone characteristics, so the choice between URS and PCNL, and even SWL can be complex. As always, patients have a right to add their own priorities into the final decision.
Virtually Required for Staghorn Stones
Unfortunately, some people form exceptionally large branched stones that can fill the entire renal pelvis and calyces. The radiograph at left shows such ‘staghorn‘ stones. They look like the horns of a stag, do they not?
Often times staghorn stones are composed of struvite created by urinary tract infection, and treatment requires skilled surgery and antibiotic treatment combined.
PCNL is the recommended treatment for staghorn stones. SWL and URS have limited success with them. If the stone does contain struvite, and is therefore infected, it’s important to try and completely remove the stone without leaving fragments behind as residual fragments can act a nidus for future stone growth and infection. As well, more common calcium stones can be infected, too, and demand special care.
How PCNL is Performed
Before undergoing surgery, patients will require routine blood work, a urine sample to rule out infection, and a CT scan to better understand anatomy and stone characteristics. Often times patients will be assessed by an Anesthesiologist to ensure that they can safely undergo a general anesthetic.
After going off to sleep, patients are most commonly positioned prone position – lying on their front. This allows access to the kidney with good working space while avoiding the bowel. Recently, some surgeons have placed patients supine – on their back. Surgeons who favor this approach say that stone free rates and overall complications are similar to prone positions, but the supine approach is faster – easier positioning, and may also lead to fewer postoperative fever events (Li 2019).
The most critical step of the procedure is gaining access to the kidney. It was special access that originated PCNL in the first place.
One inserts a needle through the back or flank and guides it into a calyx of the kidney. Once the needle is inserted into the kidney, a working sheath is inserted over a dilator. The working sheath allows the surgeon to insert scopes and instruments to fragment and remove the stones.
The drawing shows the sheath passing through the outer part of a kidney and through a papillum into the renal pelvis where a large stone resides. An instrument has been passed through the sheath to break up and remove the stone.
For most surgeons, access is performed under x-ray guidance although it can be performed with ultrasound guidance or a combination of the two. Although more technically challenging, ultrasound guidance limits radiation exposure (Liu 2017).
A third method for gaining access uses ureteroscopy to visualize the needle in real-time as it enters the kidney. The link takes you to a brief and nifty video showing the procedure. Through the optics of the ureteroscope the surgeon can confirm the correct placement of the needle. This decreases the amount of x-ray required. As well, the surgeon can use URS to help treat the stone if needed.
Recently some surgeons have adopted the Miniaturized PCNL approach. Mini PCNL requires the same procedural steps of a standard PCNL, but uses a smaller dilator and working sheath. You can see the size difference in the picture at left. The benefit of Mini PCNL is that smaller dilation decreases the risk of bleeding (Atassi 2019). The major downside is that a smaller sheath may impede removal of larger stones. Although the role of Mini PCNL is evolving, it may be an appropriate option to treat stones <2 cm in size.
Removal of the Stone
Typically, surgeons will use a combination of instruments to perform a PCNL The most useful tool to treat large stones are intracorporeal lithotripters which use a combination of ballistic and ultrasonic wave energy to break the stone into tiny pieces while simultaneously vacuuming out the fragments. The link above is to a brief movie that shows a lithotripter inside a kidney breaking up a large stone during a PCNL.
When intracorporeal lithotripters are unable to reach the stone, surgeons can use a combination of laser lithotripsy and baskets to treat the stone. The laser light has a high temperature and is used to break the stone into small pieces or dust the stone into sand. At the end the scope is pulled back through the sheath and fragments removed from the kidney,
After the stone has been treated, the entire kidney is inspected with flexible nephroscopy to attempt to identify any fragments that may have migrated during the procedure.
Post Surgical Drainage
At the conclusion of the surgery most surgeons will leave a nephrostomy tube, a ureteric stent, or a combination of both to ensure the urine from the kidney drains without obstruction.
A nephrostomy tube drains urine from the kidney through a tube using the tract established from the surgery. The left part of the picture shows the drain and its bag to collect fluid. At the right of the picture, the coiled end of the drain is shown inside the renal pelvis just where the ureter begins.
A ureteric stent is a small flexible tube that drains the urine from kidney, down the ureter to the bladder. The small picture just below shows a stent, Its coiled upper end is much like that of the drain of a nephrostomy tube, but instead of draining out through the skin, it drains into the bladder.
In recent years some surgeons have begun to favor just a ureteric stent. Compared to a nephrostomy tube, a stent may cause less post-operative pain and lung complications, and allow a shorter hospital stay and an earlier return to work (Xun 2017, Alschuler 2019). Regardless of which type of drainage tube is used, both are temporary and often removed within a week.
Post Operative Care and Discharge
Most surgeons aim for discharge after 1 day in hospital. In some centers patients are discharged home the same day of surgery. Compared to those kept overnight, patients selected for “ambulatory” PCNL tend to be healthier, have less complex stone disease, and an uncomplicated operation (Bechis 2018, Schoenfeld 2019).
Approximately 13% of patients present to emergency departments within a month after surgery (Khanna 2020). Common reasons are voiding discomfort, flank pain, and blood in the urine. More serious risks with PCNL are severe bleeding, and infection. Risk factors for bleeding include longer operative times, larger stones, multiple punctures, hypertension, diabetes and a larger tract size. The risk of bleeding requiring a blood transfusion ranges from 1-10%.
The risk of developing a post-operative infection following PCNL ranges from 2.5 – 20%. This variability is in part due the nature of the surgery and the fact that many stones are infected. Patients with bacteria in their urine pre-operatively require a full course of antibiotics prior to surgery to try and prevent post-operative fever. Patients are monitored post-operatively for signs of infection (fever, elevated heart rate, low blood pressure) and treated as needed.
Most surgeons will obtain a CT scan or a plain x-ray and ultrasound to visualize residual stones and rule out obstruction. Sometimes residual stones need to be treated, some can be observed over time. The count of residual stones is crucial to assess whether new stones are forming once medical stone prevention is in place. All removed stones and fragments must be analysed as this is crucial for long term prevention.
- Percutaneous Nephrolithotomy is a well-established treatment for large kidney stones.
- The aim of PCNL is to remove all of the stone burden with a single treatment
- The most common reasons for PCNL are stones >2 cm and lower pole kidney stones >1cm.
- Most patients will be home 1 day after surgery.
FREQUENTLY ASKED QUESTIONS
Q: Does the dilation of the kidney cause long-term damage to the kidney?
A: Following your surgery it is not uncommon to see a transient decrease in renal function. Over time, renal function typically returns to normal and can even improve, particularly if the stone was obstructing the flow of urine.
Q: What happens to the tract in the kidney after the procedure?
A: After the working sheath is removed the tract closes up on its own. Urine leak from the back is possible and typically resolves after a day or two.
Q: Do the tubes and stents cause pain?
A: The nephrostomy tube typically does not cause pain (although can be uncomfortable) but it does require that you carry around a drainage bag to collect the urine. The ureteric stent is often uncomfortable – commonly patients experience urinary frequency, urgency and blood in the urine while the stent is in place. Your symptoms will improve after the stent is removed.
Q: Do I need to stop my anticoagulation (blood thinner) before surgery?
A: Most surgeons will NOT perform a PCNL if you are taking medication to thin your blood. Before stopping blood thinners it is necessary to speak with the anesthesiologist or doctor who prescribed the medication to ensure that it is safe.
Q: How big will my scar be?
A: The incision on the back/flank is about an inch in size
Q: When will I be able to return to work?
A: Everyone recovers at their own pace, however, most patients will be able to return to work about a week after their procedure.