EURURO Vol. 72 No. 2

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1. Introduction
Kidney stone disease is considered to be an important
health issue; its incidence has increased over the years to
almost 9% Despite efforts in prevention and advances in
management methods, urolithiasis is still an important
cause of morbidity in all age groups and carries a significant
economic burden because of associated direct and indirect
costs
Percutaneous nephrolithotomy (PNL) has gained accep-
tance as the gold standard for the treatment of large renal
calculi . During the past 20 yr, the instruments used
have been miniaturized in an effort to decrease morbidity
associated with standard PNL and increase the efficiency of
stone removal. Jackman et al and Helal et al initially
used smaller instruments in 1997 for pediatric cases with
the proposed advantage of lower morbidity. Today, the term
mini-perc, or mini-PNL (mPNL), usually describes tract sizes
between 14 Fr and 22 Fr, although a clear definition does not
exist . Recently, even smaller systems—ultramini-PNL
(umPNL) using tracts sized 11–13 Fr and microperc (mPNL)
using tracts sized 4.8–10 Fr—have been introduced as
alternative modalities to reduce procedure-related morbid-
ity .
The primary goal of PNL is to achieve stone-free status
while minimizing morbidity and complications. It has been
reported that tract size is one of the main parameters
affecting the complication rate However, reducing the
tract size may adversely affect some procedure-related
factors such as operation time . We performed a
systematic review to assess the relative benefits and harms
of different PNL tract sizes for the treatment of renal stones.
2. Evidence acquisition
2.1. Search strategy
This systematic review was performed according to the
Preferred Reporting Items for Systematic Reviews and
Meta-analyses (PRISMA) statement and the Cochrane
Handbook for Systematic Reviews of Interventions
. Studies on PNL (from January 1, 2000 to October 30,
2014) were identified by highly sensitive searches of
electronic databases (Embase, Medline, the Cochrane
Central Register of Controlled Trials, and the Health
Technology Assessment Database). Studies in languages
other than English were excluded. The protocol for the
review is available on PROSPERO (CRD42015023766;
).
The articles identified were independently screened by
two reviewers (Y.R. and A.T.). Full-text articles of potentially
relevant studies were subsequently independently scruti-
nized for eligibility. Disagreements were resolved by a third
party (T.K.).
2.2. Selection of studies
We included randomized controlled trials (RCTs), nonran-
domized comparative studies (NRCSs), and single-arm
studies with at least one study arm reporting efficacy or
safety data on PNL procedures using tracts sized 22 Fr
(mPNL, umPNL, or mPNL) for treatment of renal stones in
adults (age 18 yr). Studies published as full-text articles or
as congress abstracts were included. The exclusion criteria
were: case series (single arm) of <20 patients; pediatric
studies (age <18 yr); patients with pre-existing nephros-
tomy before PNL; anatomic abnormalities (eg, horse-shoe
kidney, transplanted kidney, malrotated kidney); use of
electrohydraulic lithotripsy for stone fragmentation; and
multitract punctures (ie, more than one tract used during
procedure). However, studies fulfilling any exclusion
criterion were included if groups of patients of interest to
this review were reported separately, or if the fraction of
procedures or patients with criteria meriting exclusion
constituted <10% of the total study population.
The primary benefit outcomes were the immediate
stone-free rate (ISFR) and the stone-free rate (SFR) at a later
date (after auxiliary procedures for a period of up to 3 mo).
For this review, ‘‘stone-free’’ was defined as there being no
detectable stone fragments on radiology; if an alternative
definition was used by the trialist (eg, residual fragments
sized <4 mm), the data were reclassified accordingly. The
imaging modality used to assess stone-free status was not
considered.
The primary harm outcomes were intraoperative and
postoperative complications. These were recorded as the
incidence of grouped complications according to severity,
such as Clavien grade, or as the incidence of ad hoc
individual complications such as blood loss (as defined by
the trialist; eg, ml of blood or change in hemoglobin
concentration), the need for blood transfusions, visceral
injury, urosepsis, pneumothorax, or death.
The secondary benefits and harms outcomes were:
duration of the procedure; quality of life (QOL; as defined by
the trialist); pain (as defined by the trialist; eg, analgesic
requirement, pain scores quantified on a visual analog scale
[VAS], etc); need for a secondary procedure (procedure to
clear the stone beyond the primary procedure, including
single-arm case series, and only two of which were RCTs. Furthermore, the tract sizes used
and types of stones treated were heterogeneous. Hence, the risks of bias and confounding
were high, highlighting the need for more reliable data from RCTs.
Patient summary: Removing kidney stones via percutaneous nephrolithotomy (PNL) using
smaller sized instruments (mini-PNL) appears to be as effective and safe as using larger
(traditional) instruments, but more clinical research is needed.
# 2017 European Association of Urology. Published by Elsevier B.V. All rights reserved.
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