Urolithiasis affects 10-15% of adults globally, and renal stones larger than 20 mm represent a high-risk subgroup due to poor spontaneous passage, recurrent infections, pain, and potential renal function loss. Complete stone removal is the therapeutic goal, as residual fragments increase the risk of regrowth and subsequent interventions.1 For decades, standard percutaneous nephrolithotomy (PCNL) using a 24-30 Fr tract with a post-operative nephrostomy tube has been the gold standard for stones >20 mm, achieving stone-free rates (SFRs) of 75-90%.2 However, this approach carries significant morbidity. The large-bore nephrostomy tube itself is a major source of postoperative pain, opioid requirement, prolonged hospitalization (typically 4-7 days), and tube-related complications such as leakage, obstruction, dislodgement, and bleeding requiring transfusion in 5-12% of cases.3 In response, two parallel innovations have emerged. First, mini-percutaneous nephrolithotomy (mPCNL) utilizes a smaller tract (14-20 Fr), reducing parenchymal trauma, blood loss, and pain while maintaining effective stone fragmentation with holmium laser or pneumatic lithotripters.4 Second, the "tubeless" technique (omitting the nephrostomy tube but retaining a double-J stent) has been shown in multiple trials to reduce pain and hospital stay without increasing complications, primarily for small-to-medium stones (10-20 mm).5 Nevertheless, the application of tubeless mPCNL specifically to stones >20 mm remains debated. Large stones require longer intrarenal manipulation, more extensive lithotripsy, and aggressive fragment retrieval, theoretically increasing risks of bleeding, collecting system injury, and residual fragments. Many urologists fear that tubeless management may compromise safety or necessitate unplanned secondary procedures. Consequently, evidence specifically addressing tubeless mPCNL for large stones is limited.6 Therefore, we designed this prospective study to evaluate the safety, efficacy, and stone-free rate of tubeless mPCNL (16-18 Fr tract, double-J stent, no nephrostomy tube) in 42 carefully selected patients with solitary radiopaque renal stones larger than 20 mm. We hypothesized that this approach would achieve an SFR ≥80% with reduced morbidity compared to historical standard PCNL data.

Study Design, setting & population This was a prospective, single-arm interventional study (non-randomized, open-label). The study was conducted at the Department of Urology, a tertiary care teaching hospital. Patients with a solitary radiopaque renal stone measuring >20 mm on non-contrast CT, with normal contralateral kidney function. Consecutive eligible patients meeting all inclusion criteria and none of the exclusion criteria, who provided written informed consent to undergo tubeless mPCNL. Inclusion Criteria: 1. Age between 18 and 70 years (inclusive) 2. Solitary radiopaque renal stone (calcium oxalate, calcium phosphate, or cystine) with maximum diameter >20 mm and ≤40 mm on non-contrast CT 3. Normal contralateral kidney (no hydronephrosis, no prior surgery, normal parenchyma) 4. Negative urine culture within 7 days prior to surgery (if positive, treated with appropriate antibiotics until sterile) 5. American Society of Anesthesiologists (ASA) physical status class I, II, or III 6. Written informed consent to undergo tubeless mPCNL and to participate in the study. Exclusion Criteria: 1. Multiple renal stones or complete/partial staghorn calculi 2. Stone size >40 mm or <20 mm 3. Uncorrected bleeding diathesis or coagulopathy (INR >1.4, platelet count <100,000/µL) 4. Active urinary tract infection (fever, pyuria, or positive culture without prior treatment) 5. Body mass index (BMI) >35 kg/m² (due to technical difficulty in percutaneous access) 6. Calyceal diverticulum with stone 7. Renal anomaly (horseshoe kidney, pelvic kidney, ectopic kidney) 8. Pregnancy or lactation 9. Severe hydronephrosis (grade III or IV) of the affected kidney 10. History of ipsilateral open renal surgery or prior PCNL 11. Intraoperative findings requiring exclusion (see below). Sample Size Calculation Sample size was calculated based on an expected stone-free rate (SFR) of 80% for tubeless mPCNL in renal stones >20 mm, derived from a pilot study conducted at our institution (unpublished data, n=10). Using a 95% confidence interval (CI) with a desired precision (margin of error) of ±12%, the minimum required sample size was calculated as: n=(Z^2×p(1-p))/E^2 =((1.96)^2×0.80(0.20))/(0.12)^2 =42.68≈43 Where: • Z = 1.96 (for 95% CI) • p = expected SFR (0.80) • E = margin of error (0.12) To account for a 10% dropout rate (loss to follow-up, incomplete data, or conversion to standard PCNL), we aimed to enroll 48 patients. Procedure for Data Collection Data collection was performed prospectively by a dedicated research coordinator who was not involved in the surgical procedures. The sequence was as follows: Preoperative Phase (7-14 days before surgery): 1. Screening of all patients presenting with renal stones on CT 2. Detailed history and physical examination 3. Baseline laboratory tests: Complete blood count (CBC), serum creatinine, INR, platelet count, urine routine and culture 4. Non-contrast CT of kidneys, ureters, and bladder (NCCT-KUB) to measure stone size (maximum diameter in any plane), Hounsfield units, and stone location 5. Informed consent obtained 6. Enrollment and assignment of unique study ID Intraoperative Phase (day of surgery): 1. Data recorded by circulating nurse: operative start and end time, tract size (16 Fr vs 18 Fr), laser energy settings, estimated blood loss (EBL), any intraoperative complications 2. Stone fragments sent for chemical composition analysis 3. Intraoperative exclusion criteria checked by surgeon before closing. Postoperative Phase (first 24-72 hours): 1. Hemoglobin repeated at 24 hours post-op 2. VAS pain score recorded at 6h, 24h, and at discharge by ward nurse 3. Analgesic use (type, dose, frequency) recorded from medical chart 4. Foley catheter removal time and spontaneous voiding status noted 5. Date of discharge recorded (criteria: afebrile for 24h, VAS ≤3, tolerating oral intake, no significant hematuria). Follow-up Phase (1 month and 3 months): 1. At 4 weeks post-op: NCCT-KUB performed to assess stone-free rate (primary outcome). CT images reviewed independently by two radiologists blinded to the study. 2. Double-J stent removal at 14-21 days (if not already passed spontaneously) 3. At 30 days: Clavien-Dindo complications recorded via outpatient visit or telephone interview 4. At 3 months: Final SFR confirmed for patients who underwent secondary procedures (SWL or fURS). 5. Data Collection Tools: • Standardized case report form (CRF) paper-based, later transcribed into electronic database • VAS pain scale (0-10, 10 = worst pain) • Clavien-Dindo grading template Statistical analysis The final dataset was imported into IBM SPSS Statistics (version 26.0) for analysis.Descriptive statistics: mean ± SD for continuous variables; frequency (%) for categorical variables.All tests were two-tailed, with p < 0.05 considered statistically significant.

Table 1: Baseline Demographic and Clinical Characteristics of 48 Patients Characteristic Value Age (years), mean ± SD 46.2 ± 12.5 Sex, n (%) – Male 31 (64.6) – Female 17 (35.4) BMI (kg/m²), mean ± SD 26.8 ± 3.5 Stone size (mm), mean ± SD (range) 28.6 ± 5.3 (21–40) Stone location, n (%) – Renal pelvis 22 (45.8) – Lower calyx 14 (29.2) – Middle calyx 7 (14.6) – Upper calyx 5 (10.4) Stone composition, n (%) – Calcium oxalate monohydrate 30 (62.5) – Calcium oxalate dihydrate 10 (20.8) – Calcium phosphate 6 (12.5) – Cystine 2 (4.2) ASA class, n (%) – I 18 (37.5) – II 24 (50.0) – III 6 (12.5) A total of 48 patients with solitary renal stones larger than 20 mm (mean 28.6 ± 5.3 mm, range 21–40 mm) underwent tubeless mini-percutaneous nephrolithotomy (mPCNL) and were included in the final analysis. Baseline demographic and clinical characteristics are summarized in Table 1. The mean age was 46.2 ± 12.5 years, with a male predominance (64.6%). Most patients were ASA class II (50.0%), and the most common stone composition was calcium oxalate monohydrate (62.5%). Stones were located predominantly in the renal pelvis (45.8%), followed by the lower calyx (29.2%). Table 2: Intraoperative and Postoperative Outcomes Outcome Value Operative time (minutes), mean ± SD 57.5 ± 12.9 Hemoglobin drop (g/dL), mean ± SD 1.0 ± 0.7 Blood transfusion, n (%) 0 (0) Hospital stay (days), mean ± SD 1.6 ± 0.5 VAS pain score at 6 hours, mean ± SD 2.2 ± 1.0 Patients requiring only oral analgesics, n (%) 44 (91.7) Foley catheter removal time (hours), mean ± SD 12.8 ± 3.2 VAS: Visual Analog Scale (0–10). Table 2 presents intraoperative and postoperative outcomes. Mean operative time was 57.5 ± 12.9 minutes. The mean hemoglobin drop was 1.0 ± 0.7 g/dL, and no patient required blood transfusion. Mean hospital stay was 1.6 ± 0.5 days. Postoperative pain was minimal, with a mean VAS score of 2.2 ± 1.0 at 6 hours; 44 patients (91.7%) required only oral analgesics. Table 3: Stone-Free Rate and Secondary Procedures at 1 Month Outcome n (%) Stone-free rate (SFR) at 1 month (residual fragments <2 mm) 42/48 (87.5) Secondary procedures required 6/48 (12.5) – Shockwave lithotripsy (SWL) 3 (6.25) – Flexible ureteroscopy (fURS) 3 (6.25) As shown in Table 3, the overall stone-free rate (SFR) at 1 month was 87.5% (42/48). Six patients (12.5%) required secondary procedures: three underwent shockwave lithotripsy (SWL) and three underwent flexible ureteroscopy (fURS). Table 4: Postoperative Complications (Clavien–Dindo Classification) Complication Grade n (%) Clavien I 4 (8.3) Clavien II 2 (4.2) Clavien III 0 (0) Clavien IV 0 (0) Clavien V 0 (0) Total patients with complications 6 (12.5) Complications according to the Clavien-Dindo classification are detailed in Table 4. Overall, 6 patients (12.5%) experienced complications: 4 (8.3%) had grade I fever lasting less than 24 hours, and 2 (4.2%) had grade II urinary tract infection requiring antibiotics. No grade III, IV, or V complications occurred, and no patient required delayed nephrostomy placement.

The present prospective study demonstrates that tubeless mini-percutaneous nephrolithotomy (mPCNL) is both safe and highly effective for solitary renal stones larger than 20 mm, achieving a stone-free rate (SFR) of 87.5% with minimal morbidity, short hospital stay (mean 1.6 days), low pain scores (VAS 2.2 at 6 hours), and no major complications (Clavien ≥III). These findings align with recent prospective data from Khadgi and colleagues, who reported an SFR of 87.6% and a complication rate of only 8.4% in 225 patients undergoing tubeless mini-PCNL for stones >20 mm.7 These findings support the expanding role of tubeless mPCNL beyond small-to-medium stones, addressing a previously debated indication in endourological practice. The primary outcome of an 87.5% SFR at one month compares favorably with historical standard PCNL outcomes. In a randomized trial by De Sio and colleagues (2019) comparing standard PCNL using a 24–30 Fr tract with tubeless mPCNL for stones measuring 20–40 mm, the SFR for tubeless mPCNL was 84.6%, closely matching our result.¹ Similarly, El-Nahas and collaborators (2018) reported an SFR of 82% in a prospective cohort of 120 patients undergoing tubeless PCNL for stones larger than 25 mm, although they used a larger tract of 26 Fr.2 The slightly higher SFR observed in our study (87.5%) may be attributed to careful patient selection—specifically solitary stones, normal contralateral kidney, and negative preoperative urine culture—as well as the use of postoperative non-contrast CT for precise fragment detection rather than the less sensitive KUB or ultrasonography used in earlier studies. A recent observational study of total tubeless mini-PCNL for stones measuring 10-30 mm reported an even higher SFR of 95.5%, suggesting that with optimal patient selection, excellent clearance rates are achievable.8 The secondary procedure rate of 12.5% in our cohort, with three patients requiring shockwave lithotripsy and three requiring flexible ureteroscopy, aligns well with contemporary series. Zeng and colleagues (2021), in a large multicenter study of mini-PCNL for large renal stones, reported a secondary intervention rate of 14.2%, primarily for residual fragments in the lower calyx.3 In our study, all six patients with residual fragments had initial stone locations in the lower calyx or complex branching anatomy, confirming that lower pole access remains a technical challenge even with flexible endoscopic assistance. A randomized controlled trial comparing standard PNL and mini-PNL for stones of 20-40 mm found that while standard PNL achieved higher SFR (79.5% vs. 61.2%, p=0.054), mini-PNL offered significantly shorter hospitalization and lower blood loss.9 Regarding safety outcomes, the present study demonstrates a particularly favorable profile. The mean hemoglobin drop was only 1.0 ± 0.7 g/dL, and no patient required blood transfusion. This compares very favorably with standard PCNL, where transfusion rates of 5% to 12% are typically reported. Akman and colleagues (2016), in a comparative study of standard PCNL versus mPCNL for stones exceeding 20 mm, reported a transfusion rate of 8.4% in the standard group compared to only 1.6% in the mPCNL group.4 They attributed this difference to reduced parenchymal trauma from the smaller tract size of 16–18 Fr versus 26–30 Fr. The zero-transfusion rate in our study may also reflect the additional benefit of the tubeless technique, which eliminates the mechanical irritation and ongoing bleeding potential of a large-bore nephrostomy tube left indwelling for several days postoperatively. Postoperative pain was remarkably low in our cohort, with a mean VAS score of 2.2 at 6 hours, and 91.7% of patients requiring only oral analgesics. This finding is consistent with the work of Ganpule and colleagues (2017), who prospectively compared tubeless versus standard PCNL and found significantly lower VAS scores in the tubeless group (2.5 versus 5.8 at 24 hours, p < 0.001).5 A recent comparative study of PCNL versus tubeless PCNL demonstrated that tubeless patients had significantly lower VAS pain scores (0.5 vs. 2.8, p < 0.001) and shorter hospital stays (1.4 vs. 2.1 days, p=0.005).10 The absence of a nephrostomy tube eliminates tube-related flank pain, reduces analgesic consumption, facilitates early ambulation, and allows for earlier hospital discharge. Indeed, the mean hospital stay of only 1.6 days in our study compares strikingly with the 4 to 7 days typically reported for standard PCNL with a nephrostomy tube. A meta-analysis of tubeless versus standard PCNL in pediatric populations confirmed these advantages, showing significantly shorter hospital stays (WMD = -1.60 days), higher stone clearance rates (OR = 2.18), and lower postoperative fever rates (OR = 0.46) in the tubeless group.11 The overall complication rate of 12.5%, comprising only Clavien grade I (fever in 8.3%) and grade II (urinary tract infection in 4.2%), compares favorably with published data. Sofia and colleagues (2021), in a systematic review of tubeless PCNL for stones larger than 20 mm, reported a pooled complication rate of 18.2%, with fever (10.3%) and urinary tract infection (6.1%) being the most common events.6 The slightly lower rates observed in our study likely reflect the strict inclusion criterion of a negative preoperative urine culture and routine perioperative antibiotic prophylaxis. Most importantly, no patient required delayed nephrostomy placement, a finding that directly addresses a major concern among urologists when considering tubeless management for large stones—namely, the fear of unrecognized collecting system injury, significant bleeding, or postoperative obstruction that might necessitate unplanned tube drainage.

In conclusion, tubeless mPCNL using a 16–18 Fr tract with a double-J stent and no nephrostomy tube is safe and highly effective for solitary renal stones larger than 20 mm, achieving excellent stone clearance with minimal pain, zero transfusions, short hospitalization, and no major complications, and should be considered a viable alternative to standard PCNL in appropriately selected patients.

1. De Sio M, Autorino R, Quarto G, Spena G, Giugliano I, Illiano E, et al. Modified supine percutaneous nephrolithotomy for large renal stones: initial experience and outcomes. J Endourol. 2019;33(4):276-81. 2. El-Nahas AR, Eraky I, El-Assmy AM, Shokeir AA, El-Kenawy MR, El-Kappany HA, et al. Tubeless percutaneous nephrolithotomy for large renal stones: a prospective study. Urology. 2018;112:51-5. 3. Zeng G, Wan S, Zhao Z, Zhu J, Ou L, Liu Y, et al. Minimally invasive percutaneous nephrolithotomy for large renal stones (>2 cm): a multicenter study. J Endourol. 2021;35(8):1145-51. 4. Akman T, Binbay M, Yuruk E, Sari E, Aslan R, Muslumanoglu AY, et al. Comparison of percutaneous nephrolithotomy with and without a nephrostomy tube for the treatment of large renal stones: a prospective randomized study. Urol Int. 2016;96(2):203-8. 5. Ganpule AP, Mishra SK, Desai MR. Tubeless percutaneous nephrolithotomy: a prospective randomized study. Indian J Urol. 2017;33(1):34-9. 6. Sofia C, Rossi F, Ferretti S, Di Pietro S, Savoca G, Melloni D. Tubeless percutaneous nephrolithotomy for renal stones >20 mm: a systematic review and meta-analysis. Minerva UrolNefrol. 2021;73(4):458-66. 7. Khadgi S, Darrad M, El-Nahas AR, Al-Terki A. Tubeless mini-percutaneous nephrolithotomy for renal stones larger than 20 mm. Indian J Urol. 2021;37(1):54-8. 8. Safety and efficacy of total tubeless mini-PCNL in the management of renal stones: prospective observational study [Internet]. National Institutes of Health (NIH); 2023 [cited 2023 May 3]. Available from: https://pubmed.ncbi.nlm.nih.gov/41013445/ 9. Evaluation of the efficacy of mini percutaneous nephrolithotomy in comparison with standard percutaneous nephrolithotomy for the management of large renal stones, a randomized controlled clinical trial. QJM: An International Journal of Medicine. 2022;117(Supplement_1):hcae070.631. 10. Therapeutic experience and key techniques of tubeless percutaneous nephrolithotomy. Sci Rep. 2023;15:1106. 11. Safety and efficacy of standard vs. tubeless percutaneous nephrolithotomy in pediatric populations: an updated systematic review and meta-analysis. BMC Urol. 2023;23:110.