Introduction
During endoscopic stone surgery, both Holmium:YAG (Ho:YAG) and Thulium Fiber Laser (TFL) technologies are employed to break down urinary stones into minute particles, often referred to as DUST. However, a universally accepted definition of what constitutes DUST in this context remains elusive. Similarly, the understanding and definition of Clinically Insignificant Residual Fragments (CIRF) are crucial for patient management and outcomes following stone removal procedures. This review aims to clarify and define both stone DUST and CIRF based on current literature. Understanding these definitions is vital for comparing the effectiveness of different laser technologies and assessing post-operative patient status.
Methods for Defining DUST and CIRF
To establish clear definitions, a comprehensive search was conducted across Embase, MEDLINE (PubMed), and Cochrane databases. The search encompassed both in vitro and in vivo studies related to DUST and CIRF. Keywords used included “dust,” “stones,” “urinary calculi,” “urolithiasis,” “residual fragments,” “dusting,” “fragments,” “lasers,” and “clinical insignificant residual fragments.” This rigorous approach ensured a broad capture of relevant research to inform the definitions.
Defining Stone DUST: In Vitro and Clinical Relevance
DUST, in the context of urinary stone fragmentation, refers to the fine pulverization of stones. In vitro studies define DUST as particles that float spontaneously with a sedimentation duration of 2 seconds or more. Crucially, these particles should be aspirable through the 3.6Fr working channel (WC) of a flexible ureteroscope (FURS). A consensus appears to be forming around an upper size limit of 250 µm for DUST particles. Various laser technologies, including Ho:YAG (with and without “Moses Technology”), TFL, and pulsed-Thulium:YAG (pTm:YAG), are capable of producing DUST. However, current perioperative technologies lack the ability to precisely measure DUST particle size in real-time during surgery. It is worth noting that TFL and pTm:YAG have demonstrated superior dusting capabilities compared to traditional Ho:YAG lasers. Therefore, the definition of DUST relies on both particle size and practical aspirability through standard surgical equipment.
Defining Clinically Insignificant Residual Fragments (CIRF)
CIRF pertains to residual fragments (RF) remaining after stone surgery that are not expected to cause immediate stone-related complications. These complications include loin pain, acute renal colic, or the need for further medical or interventional retreatment. The size definition of CIRF has evolved over time. Older studies, primarily based on Shock Wave Lithotripsy (SWL), defined CIRF as fragments ≤ 4 mm. More recent research, particularly in the context of FURS and Percutaneous Nephrolithotomy (PCNL), has refined this definition to ≤ 2 mm for FURS and ≤ 4 mm for PCNL, reflecting the different surgical approaches and their associated outcomes. Importantly, residual fragments ≤ 2 mm are associated with lower rates of stone recurrence, regrowth, and subsequent clinical events. While Non-Contrast Computed Tomography (NCCT) is recommended for postoperative CIRF evaluation, there is no standardized diagnostic method to precisely assess the presence and quantity of DUST postoperatively.
Conclusion: Independent Definitions of DUST and CIRF
In conclusion, DUST and CIRF represent distinct and independent entities in the realm of endoscopic stone surgery. DUST is defined in vitro by a particle size criterion of ≤ 250 µm and clinically by the ability to be fully aspirated through a 3.6Fr-WC. CIRF, on the other hand, is defined as ≤ 2 mm RF on postoperative NCCT for FURS procedures, and ≤ 4mm for PCNL, representing fragments unlikely to cause immediate clinical issues. These clear definitions are essential for standardized reporting, research, and comparison of different surgical techniques and laser technologies in the management of urinary stones. Further research may focus on developing intraoperative techniques to quantify DUST production and optimize surgical strategies for minimal residual fragments.
