Indications for intervention
Percutaneous access is indicated when extracorporeal shock wave lithotripsy is ineffective or impossible.
Main indications:
- Large renal pelvis stones (pelvis renalis) measuring more than 2 cm.
- Staghorn calculi (staghorn calculi).
- Lower pole calyx stones (calyx renalis inferior) larger than 1 cm.
- Calculi in the presence of impaired drainage (horseshoe kidney, diverticular stones).
Relative indications:
- Very dense formations (CT density exceeds 1000 HU).
- Cystine stones.
In rare cases, access is used for resection of transitional cell carcinoma of the renal pelvis, foreign body removal, or balloon dilation of pelviureteric junction (PUJ) strictures.
Planning and access selection
A critically important step before starting the puncture is understanding the patient's intrarenal anatomy. A high-quality three-dimensional (3D) CT pyelogram is used for this purpose. The entry point is planned to ensure good endoscopic navigation and maximum stone clearance.
Renal access options:
- Through the posterior calyces. This is the optimal route, providing convenient access to the anterior calyces. Direct puncture of the anterior calyces makes intrarenal navigation extremely difficult.
- Through the upper pole. Allows deep access to the pelviureteric junction and the upper third of the ureter. The disadvantage of the method is the increased risk of injury to the pleura or the posterior branch of the renal artery.
- Through the lower pole. Can be challenging in the case of an acute infundibulopelvic angle (making it difficult to reach the distal part of the pelvic stone).
General rule: if removing all stones is impossible, the surgeon must clear the renal pelvis to eliminate kidney obstruction. It is also important to drain the lower calyces, as residual fragments from there cannot drain naturally.
Stages of puncture performance
The intervention is most commonly performed with the patient in the prone position, although the supine approach is also acceptable. The procedure is performed under C-arm guidance.
- Visualization: The collecting system is contrasted by intravenous administration of a radiopaque agent. If necessary, air or carbon dioxide can be used to locate narrow infundibula (e.g., in diverticula).
- Positioning: The instrument is projected over the target calyx. The needle is inserted strictly perpendicularly. Correctness of the axis is confirmed when the needle appears as a dot on the screen (bull's-eye view).
- Advancement: The C-arm is switched to an oblique view. Synchronous displacement of the needle with the patient's respiration confirms its passage through the renal capsule.
- Fixation: Upon obtaining urine from the needle, a guidewire is advanced into its lumen and coiled into a loop within the calyx. Ideally, two guidewires are placed: a stiff (working) one and a safety one.
- Dilatation: A puncture tract is created over the guidewire using balloon, serial plastic, or concentric metal dilators. Then, a working sheath (Amplatz sheath) is placed.
Complications and their management
Like any invasive procedure, percutaneous nephrolithotomy carries risks. A major international study highlights the following complication rates:
- Bleeding (7.8%): The most frequent issue. Despite the high frequency, the need for angiographic embolization arises in less than 1% of cases. Hemostatic plugs are sometimes used for prevention, but their efficacy lacks a strong evidence base.
- Pelvic perforation (3.4%): Managed primarily with adequate drainage.
- Pleural effusion (1.8%) and pneumothorax: Require symptomatic treatment or pleural cavity drainage.
- Bowel injury: Initially managed conservatively to allow fistula tract formation; surgical correction is required if conservative management fails.
A specific delayed complication is the formation of a pseudoaneurysm (pseudoaneurysm), which may manifest as bleeding weeks or even months later. When detected on angiography, embolization coils are placed into the lumen to stop the blood flow.
Stenting as a stage or alternative
Following PCNL or stricture dilatation, ureteral stenting is often required. It acts as a scaffold and ensures natural urine outflow, sparing the patient from external drains.
Modern stents include plastic ones (e.g., double pigtail type — double pigtail) and nitinol metallic mesh stents (with polymer coatings). Metal stents are less prone to ingrowth into the wall and can be used for long-term stenting. It is important to remember that all stents cause reactive urothelial hyperplasia and reduce ureteral peristalsis. Early outflow through the stent is exclusively passive.
Briefly: answers to topical questions
What imaging methods are used for guidance during renal puncture?
Fluoroscopy, ultrasonography, and computed tomography, as well as their combinations, are used for guidance during renal puncture.
- Fluoroscopic guidance (fluoroscopic) — allows visualization of needle advancement and the opacified collecting system.
- Ultrasound guidance (ultrasound-guided) — routinely used in cases of a dilated pelvicalyceal system.
- CT guidance (computed tomography-guided) — used either alone or in combination with fluoroscopy.
- Combined guidance — a combination of ultrasound and fluoroscopy or CT and fluoroscopy.
What methods exist for the prevention of infectious complications during percutaneous nephrolithotomy?
Medication and technical methods are used to prevent infectious complications during percutaneous renal interventions.
- Antibiotic prophylaxis — low-risk patients are prescribed a single dose of a broad-spectrum antibiotic, whereas high-risk patients require continuation of therapy based on urine culture. Patients at risk of pyonephrosis must receive antibiotic premedication.
- Adequate hydration — ensured before the procedure begins.
- Manipulative technique — overdistension and excessive manipulation within the collecting system must be avoided, as they increase the risk of bacteremia.
The "dart" sign — the needle points directly at you. If the needle appears as a round dot on the X-ray screen (with no visible length), it means the puncture axis is directed strictly perpendicularly and hitting right on target.
Class and exam questions
What is the difference between standard and mini-PNL?
The difference lies in the caliber of the working sheath used. In the standard procedure, the tract is dilated up to 30 F, whereas micro- and mini-access approaches use instruments with a diameter of 16–24 F to reduce tissue trauma.
Why is it necessary to clear specifically the lower calyces during incomplete removal of a staghorn stone?
Unlike the middle and upper calyces, stone fragments from the lower pole cannot spontaneously exit (drain) with the urine flow due to gravity and anatomical location. They frequently cause recurrences.
How is a nephrostomy catheter reliably secured?
The "Roman sandal" technique (Roman sandal configuration) is applied: a suture passed through the skin is tightly wrapped in a crisscross fashion around the adhesive tape on the tube, and then a reverse knot is formed. The construction is additionally covered with an adhesive fixation dressing.
What else to study on this topic
- Access features for caliceal diverticular stones
- Comparative characteristics of plastic and metal ureteral stents
- Pathophysiological urothelial reactions to foreign body (stent) placement
- Technique of antegrade ureteral stenting
- Methods of renal pseudoaneurysm embolization
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