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The Future of Stone Management
treatments was emphasised by another study by Skenazy et al.,
6
Figure 1: 5F Ureteric Catheter Compared with 4.5–8.5F
who demonstrated a significant difference in the initial therapy for
Semi-rigid Ureteroscopes
nephrolithiasis strongly related to geographical location, year of
residency completion and percentage of managed-care patients in
a urologist’s practice. Given the complexity of the treatment of large
renal stones, a dedicated stone centre may provide the best
treatment and educational resources.
7
Stone Imaging
There is no doubt that stone size has decreased dramatically in
western countries due to improved diagnostic and therapeutic
tools. Any modern imaging modality for stone detection requires a
high specificity and sensitivity. In addition, modern requirements
are acute onsite availability for emergency cases and the ease of
interpreting results obtained. Non-contrast enhanced spiral
computed tomgraphy (CT) scans seems best to combine all of
Figure 2: 6.5F Flexible Ureteroscope Accessing Lower
Renal Calyx with a 0.125mm Holmium Laser Probe
these necessities (see Figure 3). In addition, Connolly et al.
8
In Situ
demonstrated in their study that even the urology registrar
detected 51 of 54 stones at non-contrast-enhanced spiral CT with
sensitivity, specificity and positive predictive values of 94.5, 93.5
and 94.5%, respectively. This was virtually equal to findings by a
specialist radiologist and a senior urologist. This underlines the fact
that non-contrast spiral CT is an effective diagnostic tool for stone
diagnosis and allows rapid and accurate evaluation of the urinary
tract. Another promising finding was the difference in CT density of
the renal papillae of stone-formers and non-stone-formers.
9
The
mean Hounsfield density of papillae in stone patients was
significantly greater than that of control patients (50.9 versus
36.4; p<0.0001), but there is no difference in kidneys with and
without stones in patients with nephrolithiasis. In future this could
be useful in predicting patients at risk of developing nephrolithiasis.
Figure 3: Left Proximal Ureteric Stone Immediately
Furthermore, non-contrast CT may improve patient selection for
Diagnosed at Spiral Computed Tomography Scan on
SWL or more invasive treatment. Kacker et al.
10
found that average
Intravenous Pyelogram After Four Hours
stone attenuation was the best independent predictor of SWL
success. However, further refinement of this finding is still needed.
Pathophysiology and Medical Treatment
Stones are a highly recurrent disease. Unsurprisingly, prevention
of stone recurrence is achievable only by identifying
pathophysiological and molecular mechanisms of stone formation.
Asplin et al.
11
requested radiological studies to identify the overall
stone burden and to monitor treatment. For patients with a single
stone, an abbreviated laboratory evaluation was regarded as
sufficient, but for recurrent stones 24-hour urine chemistry is
mandatory to identify abnormalities and to guide dietary and plaque. Therefore, it is likely that the granules in human kidneys
pharmacological therapy. fulfil analogous functions in calcium homeostasis. This may add to
basic knowledge involved in the formation of human kidney stones.
Netelenbos et al.
12
presented risk factors associated with recurrent Another interesting finding was presented by Gao et al.,
14
who
stone formation. Hypercalciuria, hypocitraturia and urinary tract identified a polymorphism of matrix Gla protein gene, a potent
infections had odds ratios for active stone formation above 2.5, calcification inhibitor that was associated with kidney stones (OR
but 0.38 for a positive family history only. Hyperuricosuria, 0.51, 95% confidence interval [CI] 0.30–0.87; p=0.012). The G-allele
hyperoxaluria and a low urinary volume did not influence the risk of carrier had a two-fold decreased kidney stone risk compared with
active stone formation. The risk profile for active stone formation A-allele carriers in single nucleotide polymorphism 11 (OR 0.55,
versus urolithiasis in general differs significantly. Therefore, 95% CI 0.31–1.00; p=0.047). They concluded that functional assays
metabolic evaluation and determination of those risk factors might of the polymorphism should permit better understanding of the role
improve the therapeutic regimen. Ryall et al.
13
looked at various of matrix Gla protein genetic variants and kidney stones.
ways to control the formation of biominerals. His research centred
on electron-dense granules resembling calcified nanobacteria, Holmes et al.
15
questioned the role of dietary oxalate on kidney
which are remarkablly similar in general structure and composition stone formation. The only difference identified to date between
to particles observed in healthy human kidneys and in Randall’s normal individuals and those who form stones is in the intestinal
EUROPEAN UROLOGICAL REVIEW 79