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using electromagnetic sensors and the SonixGPS navigation
system had 100% success at the first attempt
[13,19],
proving to be the most effective. This high success rate can
be explained by the ability of the two systems to define and
adjust the needle path in real time. These new techniques
allow knowledge of the position of the needle relative to the
desired renal calyx for puncture throughout the procedure.
The rate of success for puncture at the first attempt was only
73.3% for the optical system incorporated in the needle
[16] ;this technique does not provide an ideal path for the needle,
which explains the lower rate. In one study of marker-based
iPad-assisted puncture, the success rate for puncture at the
first attempt was 68.4%
[17]. In this technique it is not
possible to redirect the needle during puncture, and the
patient must be in the same position during preoperative CT
and the procedure, so there may be some errors in the path.
The success rate for puncture at the first attempt was 58.3%
using Uro-Dyna-CT for laser-assisted puncture of the renal
collecting system
[19]. Although this technique shows the
direction of the needle trajectory and allows adjustment
during the procedure, it is markedly impaired by renal
movement caused, for example, by the patient breathing. In
an in vitro experiment the same technique had a success
rate of 80% for the first attempt
[18] ,suggesting that it may
need to be enhanced before regular use is feasible.
Puncture techniques guided by electromagnetic sensors
also seem to offer a shorter learning curve, with only
12 cases required to reach the level of expert surgeon
[10],
which is much lower than the 60 cases previously reported
for standard techniques
[6]. Ultrasonography using
SonixGPS navigation for puncture of the renal collecting
system is also easier than conventional techniques, as the
needle position can be monitored throughout the procedure
[20]. The optical system incorporated in the needle does not
seem to facilitate percutaneous puncture because it only
improves visualization when the needle is already in the
collecting system. The model that uses an iPad and markers
shows that an expert surgeon takes longer to perform a
puncture than a training surgeon. This technique is more
difficult for an expert surgeon than the conventional
approach
[17]. The Uro-Dyna-CT technique is also difficult
to perform and learn
[19].
All the ionizing radiation received during patient
diagnosis, treatment, and follow-up is cumulative, and
may contribute to a higher risk of malignant transformation
[22]. Thus, avoidance of the use of such radiation in PCNL is
very important. Puncture of the renal collecting system
assisted by electromagnetic sensors effectively avoids
ionizing radiation, as the surgeon does not need fluoro-
scopic guidance. Puncture of the renal collecting system
with an optical system incorporated in the needle does not
use ionizing radiation because the camera system at the
needle tip allows visualization of the renal collecting system
in real time, and use of fluoroscopy is not necessary. The
SonixGPS system also avoids ionizing radiation by creating
the path and by the knowledge of needle positioning in real
time. However, the latter two techniques use ultrasound,
and in complicated cases (such as obesity and anatomical
abnormalities) fluoroscopy must be used because ultra-
sound is compromised in these circumstances. The two
other techniques rely on ionizing radiation: the average
radiation exposure dose is 377.5
m
Gy/m
2
for marker-based
iPad-assisted puncture of the renal collecting system
[17]and 5850
m
Gy/m
2
for Uro-Dyna-CT for laser-assisted
puncture
[19] .Both systems have a higher radiation dose
than conventional fluoroscopy. Moreover, the Uro-Dyna-CT
technique involves a very significant increase in costs
[19] .There are a number of limitations of this study that need
to be recognized. The sample size is small, as this was
conceived as a feasibility study in a highly selected
population. Therefore, the technique and technology will
need to be tested in more challenging cases, such as large
stone burdens filling the renal pelvis and lower pole, as it may
be difficult to place the catheter with the electromagnetic
sensor in the desired calyx in such cases. In addition, we did
not test the system in obese patients. In this regard, we know
that the longer the distance between the electromagnetic
field generator and the sensor, the more likely is signal loss.
Therefore, further investigation in a larger sample and with
different study populations is certainly needed.
Moreover, in some patients it might not be possible to
introduce the flexible ureterorenoscope because of a tight
or narrow ureter. In this scenario we would proceed with a
standard technique for kidney puncture, which of course we
believe should be part of the surgical skills of anybody
performing PCNL.
In addition, one might argue that ureteroscopy-assisted
combined access might translate into higher costs in terms
of both probes and total resources used. The system itself is
not commercially available yet and therefore a specific cost
cannot be provided. Moreover, it was beyond the scope of
this study to perform a cost assessment, which would
require a more complex analysis that should take multiple
factors into consideration. Finally, whether there are any
harmful effects from these electromagnetic sensors in
humans remains undetermined
[23] .5.
Conclusions
A novel navigation system using real-time electromagnetic
sensors can be safely and effectively used in the clinical
setting for puncture of the renal collecting system during
PCNL. This new technology overcomes some of the intrinsic
limitations of standard fluoroscopy- and ultrasound-based
techniques. These encouraging preliminary findings need to
be validated in further clinical investigations using this
novel technology.
Author contributions:
Estevao Lima had full access to all the data in the
study and takes responsibility for the integrity of the data and the
accuracy of the data analysis.
Study concept and design:
Lima, Rodrigues, Joa˜o Vilac¸ a.
Acquisition of data:
Lima, Mota, Dias, Carvalho.
Analysis and interpretation of data:
Lima, Mota, Dias, Carvalho.
Drafting of the manuscript:
Lima, Rodrigues.
Critical revision of the manuscript for important intellectual content:
Lima,
Correia-Pinto, Autorino, Joa˜o Vilac¸ a.
Statistical analysis:
Lima, Autorino.
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