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Association Between Sampaio Pelvicalyceal System Anatomy and Surgical Outcomes in Retrograde Intrarenal Surgery

This retrospective study of 128 patients undergoing retrograde intrarenal surgery suggests that Sampaio pelvicalyceal system anatomy influences surgical outcomes, with subtype B2 independently associated with significantly higher stone-free rates compared to subtype A1.

Original authors: Tuncer Bahceci, Mustafa Tıpırdamaz, Ozan Aydogan, Burak Güler, Cagatay Ozsoy, Akif Erbin, Umut Alkan, Mustafa Gok, Alparslan Unsal

Published 2026-06-24

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Tuncer Bahceci, Mustafa Tıpırdamaz, Ozan Aydogan, Burak Güler, Cagatay Ozsoy, Akif Erbin, Umut Alkan, Mustafa Gok, Alparslan Unsal

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your kidney isn't just a simple bean-shaped bag; it's a complex, branching network of tunnels and rooms, much like a cave system inside a mountain. Some caves have wide, open hallways, while others have narrow, twisting corridors that are hard to navigate.

This research paper is essentially a report on how the shape of these "caves" affects the success of a specific surgery used to remove kidney stones.

The Mission: The "Reverse Tunnel" Surgery

The surgery in question is called Retrograde Intrarenal Surgery (RIRS). Think of it as a rescue mission where doctors don't cut into the back (which would be like drilling into the mountain). Instead, they send a tiny, flexible camera and laser tool up through the patient's natural plumbing (the urethra and bladder) and into the kidney.

Once inside, the doctor has to navigate the stone-filled "caves" to break the stones into dust or small pieces so they can be washed out. The big question the researchers asked was: Does the layout of the kidney's tunnels make this mission easier or harder?

The Map: The Sampaio Classification

To answer this, the researchers used a specific map called the Sampaio Classification. They divided kidney layouts into four distinct "architectural styles," labeled A1, A2, B1, and B2.

Think of these types like different floor plans for a house.
Type A1 is like a house with a confusing layout where the middle rooms connect to both the upstairs and downstairs in a way that might trap things.
Type B2 is like a house with a very direct, open hallway that leads straight to the exit.

The Study: What They Did

The team looked back at the records of 128 adult patients who had this surgery between 2020 and 2025. They grouped these patients based on which of the four "architectural styles" (A1, A2, B1, or B2) their kidneys had.

They then compared the results to see if the "floor plan" of the kidney predicted whether the surgery was a total success (getting rid of all stones) or if some tiny pieces were left behind.

The Findings: The "B2" Advantage

Here is what they discovered, using simple terms:

The "Floor Plan" Matters: The shape of the kidney's internal tunnels did seem to influence the outcome.
The Winner (B2): Patients with the B2 kidney layout had the best results. About 86% of them were completely stone-free after surgery. It's as if their kidney "hallways" were wide and straight, making it easy for the doctor to reach the stones and for the debris to wash out.
The Struggle (A1): Patients with the A1 layout had the lowest success rate, with only about 56% becoming stone-free. Their kidney layout seemed to make it harder to reach every corner or clear out the fragments.
The Middle Ground: The other two types (A2 and B1) fell somewhere in between, but the difference wasn't as dramatic as the gap between A1 and B2.

The "Statistical" Twist

The researchers were very careful. While the B2 group did much better than the A1 group, when they looked at the entire group of four types together, the difference wasn't "statistically significant" in the strictest mathematical sense (meaning it could have been a fluke in a smaller sample).

However, when they ran a deeper analysis to see what factors independently predicted success (ignoring stone size, stone hardness, or patient age), the B2 layout stood out. It was the only factor that consistently predicted a higher chance of being stone-free.

The Bottom Line

The paper concludes that how your kidney is built inside matters.

If you have a B2-style kidney, the "tunnels" are likely set up in a way that helps the surgeon clear stones effectively.
If you have an A1-style kidney, the "tunnels" might be more complex, making it harder to get every single stone fragment out.

The authors suggest that knowing a patient's specific "kidney floor plan" (Sampaio type) before surgery could help doctors predict how well the surgery will go and explain the risks to the patient. It's like a mechanic looking at a car's engine layout before deciding how difficult a repair will be.

Important Note: The study is based on looking back at past data (a retrospective study) from a single hospital. The authors say we need more studies in the future to confirm these findings, but the initial results suggest that the internal shape of the kidney is a key piece of the puzzle.

Technical Summary: Association Between Sampaio Pelvicalyceal System Anatomy and Surgical Outcomes in Retrograde Intrarenal Surgery

Problem Statement
Retrograde intrarenal surgery (RIRS) is a standard minimally invasive treatment for renal stones; however, achieving a stone-free (SF) status remains influenced by patient, stone, and anatomical factors. While lower-pole anatomical parameters (e.g., infundibulopelvic angle, infundibular length, and width) are known to affect fragment clearance, the broader architecture of the pelvicalyceal system (PCS) is often underreported in RIRS studies. Existing literature frequently lacks systematic evaluation of PCS branching patterns, relying instead on limited lower-pole metrics that may suffer from interobserver variability. The Sampaio classification, which delineates PCS anatomy into four subtypes (A1, A2, B1, B2) based on mid-renal-zone drainage patterns, offers a comprehensive anatomical framework, yet its specific role in predicting RIRS outcomes remains unclear. This study aimed to evaluate whether preoperative Sampaio classification is associated with postoperative SF status, residual fragments, and operative time.

Methodology
The study was a single-center, retrospective observational cohort conducted at Aydın Adnan Menderes University Faculty of Medicine between January 1, 2020, and September 30, 2025.

Population: 128 consecutive adult patients undergoing unilateral RIRS for renal stones were included after applying strict exclusion criteria (e.g., stone size >3 cm, multiple stones, urinary system anomalies, preoperative double-J stenting, or lack of preoperative CT urography).
Classification: Patients were categorized into four groups based on the Sampaio PCS subtype: A1 ( $n=36$ ), A2 ( $n=31$ ), B1 ( $n=39$ ), and B2 ( $n=22$ ).
Imaging: All patients underwent preoperative CT urography (CTU). Two experienced radiologists reviewed images via consensus to determine Sampaio subtypes and measure anatomical parameters (infundibulopelvic angle, infundibular length, and width).
Surgical Protocol: Procedures were performed under general anesthesia using digital flexible ureteroscopes and a 35-W pulsed Ho:YAG laser. A suction ureteral access sheath was used when feasible.
Outcomes: The primary outcome was postoperative SF status, defined as no residual fragments or clinically insignificant residual fragments (CIRFs) <4 mm, assessed 30 days post-surgery. Secondary outcomes included operative time and complications (Clavien-Dindo grading).
Statistical Analysis: Comparisons utilized ANOVA or Kruskal–Wallis tests for continuous variables and chi-square/Fisher's exact tests for categorical variables. Univariable and multivariable logistic regression analyses were performed to identify independent predictors of SF status, adjusting for stone size, density, and location.

Key Results

Baseline Characteristics: Demographic data and stone-related characteristics (size, volume, density, location) were comparable across all four Sampaio subtypes.
Anatomical Differences: Infundibular width was the only radiological parameter showing a significant overall difference among subtypes ( $p=0.031$ ), though post-hoc pairwise comparisons did not yield statistically significant differences after Bonferroni correction.
Surgical Outcomes:
- Stone-Free Rates: The B2 subtype demonstrated the highest SF rate (86.4%), while the A1 subtype had the lowest (55.6%). However, the overall comparison across all four groups did not reach statistical significance ( $p=0.109$ ).
- Pairwise Analysis: Exploratory pairwise analysis showed a significant unadjusted difference between B2 and A1 ( $p=0.021$ ), but this lost significance after Bonferroni correction ( $p=0.126$ ).
- Regression Analysis: In multivariable logistic regression, the Sampaio B2 subtype was independently associated with a higher likelihood of achieving SF status compared to the A1 subtype (Odds Ratio: 5.52, 95% CI: 1.36–22.34; $p=0.017$ ). Conventional factors such as stone size, stone density, and lower-pole location were not independent predictors in this model.
Complications: Only two adverse events occurred in the entire cohort (one pyelonephritis, one death), precluding statistical comparison of complication rates.

Significance and Claims
The authors conclude that Sampaio pelvicalyceal system anatomy may be an independent predictor of stone-free outcomes following RIRS. Specifically, the study suggests that the B2 subtype is associated with more favorable postoperative results compared to the A1 subtype. The authors posit that the B2 anatomy may facilitate a more direct drainage pattern toward the renal pelvis, aiding endoscopic access and fragment clearance, whereas the A1 configuration (involving complex midzone calyceal drainage) may impede complete clearance.

The paper modestly frames these findings as preliminary evidence. It acknowledges that while the overall group comparison was not statistically significant, the independent association observed in multivariable analysis indicates that the Sampaio classification captures anatomical nuances not fully reflected by conventional lower-pole measurements. The authors emphasize that these results require validation through larger, prospective, multicenter studies with standardized imaging and surgical techniques before the classification can be definitively adopted for preoperative risk stratification.