Zero residual fragment ureteroscopy: from possibility to reality – an EAU endourology perspective

Residual fragments (RF) are a challenge in flexible ureteroscopy (FURS), often leading to re-intervention. In real-world practice, the FLEXOR registry showed that 21.7% of patients have RF, with 51.5% requiring re-intervention within 3 months for FURS without use of suction. ¹ Although this RF was based on post-procedure imaging according to the local standard of care, which included KUB X-ray and/or ultrasound or non-contrast computed tomography (CT) scan. Machine learning models achieve 81% accuracy in predicting factors associated with RF ² , and yet despite the best practice using high-power lasers and scopes, until suction techniques emerged, achieving a single-stage 100% stone-free status (SFS) was unpredictable. ³ As highlighted by Tzelves et al., suction via ureteral access sheaths, catheters or scopes enhances trifecta of FURS outcomes by improving stone-free rates (SFR), reducing infectious complications and re-intervention.^3-5 EAU endourology section views suction as the future of endourology in advancing RIRS as the leading intervention for urolithiasis. ⁶

It was only after the global study highlighted the use of flexible and navigable suction ureteral access sheath (FANS) as a technique and tool instrumental in achieving zero residual fragments (ZRFs), that it became universally feasible to consider ZRF or 100% SFS as a reality in FURS, at least in adult kidneys with normal anatomy. ⁷ It was finally possible to navigate and aspirate dust, debris and multiple fragments from every part of the pelvicalyceal system (PCS) under direct visualization. ⁸ Indeed, this begs the question that should urologist completely move towards using a FANS sheath for every patient? ⁹ Whilst this is debatable, Castellani et al, have advocated that as FANS significantly improves SFR and faster recovery, it is perhaps the better alternative to conventional sheaths should a surgeon choose to use a ureteral access sheath (UAS). ¹⁰

What ZRF surgery in urolithiasis entails is to ensure complete stone removal, minimizing the need for subsequent interventions due to RF and improving single intervention operative and patient outcomes. Reportedly, this was the foundation of advocating robotic pyelolithotomy ¹¹ as even with percutaneous nephrolithotomy (PCNL), the Endourologic Disease Group for Excellence (EDGE) research consortium confirmed that RF (2–4 mm) are possible and problematic for patients. ¹² Well proven by Li Puma et al. ¹³ and Kingma et al. ¹⁴ smaller RF (2–5 mm), alluded to as clinically insignificant RF (CIRF) have the potential of regrowth and larger fragments (6–9 mm) clinically significant RF (CSRF) increased risk of stone related events. Hence, CIRF, CSRF are perhaps good for patient counselling or manage expectations but unreliable as predictors of intervention success. In fact, several inconsistencies exist even in their very definitions and diagnosis, ¹⁵ and hence, strengthens the case for ZRF diagnosed on non-contrast CT as the best outcome for any endourology intervention including FURS.

The concept of ZRF in FURS was first hypothesized by Schoenthaler et al. in 2012. ¹⁶ They anticipated that achieving ZRF would require significant technical and financial resources. With suction and technological advancements in access sheath designs, ¹⁷ factors and strategies for optimizing ZRF are finally a reality. ZRF-RIRS not only ensures complete stone removal or reduced need for additional interventions but also minimizes need for post-operative ureteral stent placement. ¹⁸ An over 90% correlation of surgeon reported intra-operative 100% SFR assessment and post-operative imaging reported 100% clearance is now possible. This is useful to improve the patient counselling and surgeons overall experience of the procedure. ¹⁹

Modern FURS with FANS is increasingly used to achieve immediate CT-proven complete SFR, even in cases of large stone burden, lower pole stones, solitary kidneys, children, bilateral and ureteral stones.^{20 –22} Studies highlight that ZRF is only possible when surgeons carefully navigate the sheath throughout the PCS and mandatorily aspirate fragments, dust and debris from the kidney. From possibility to achievable reality as early as 24 h, ²³ even with other FURS modalities like direct in scope suction (DISS), ²⁴ ushers in an era of paradigm shift, where ZRF in every case should become the new norm. True SFR based on post-operative CT scan are under 50% with FURS without suction, ²⁵ while the definition of SFR has previously varied from no residual fragments to <4 mm with different imaging modalities. ⁴ Using FANS, on CT criteria of zero fragment, only 56% were stone-free. ¹⁹ Similarly in a multicenter, prospective, randomized trial, Matlaga et al. reported that the suction technology of steerable ureteroscopic renal evacuation (SURE) was noninferior to standard ureteroscopy and stone clearance and RV were significantly better with SURE, independent of baseline stone volume. ²⁶ Although zero fragment rate (ZFR) is ideal, we are still far from reaching that epitome of success.

The potential importance of ZRFs can be summarized as seen in Table 1.

Table 1.

Potential importance of ZRFs.

Benefit	Description
Reduced risk of recurrent stone disease	Residual fragments can serve as a nidus for new stone growth, increasing the risk of recurrent nephrolithiasis.
Minimized need for re-interventions	Residual fragments can become symptomatic necessitating further procedures to address the same.
Improved patient outcomes	Achieving ZRF reduces the risk of complications associated with stone-related events, such as urinary tract infections, renal colic and stone enlargement.
Improved cost benefits to patients	Reduced healthcare costs and patient burden of related expenses on kidney stone disease intervention.

ZRF, zero residual fragment.