Srinivas Kalabhavi1, Pramod Makannavar2, Revanasiddappa Kanagali3, Prabhath A.N.4, Narendrakumar Shah5
BACKGROUND
Dual energy computed tomography (DECT) is a new method of computed
tomography (CT) imaging which allows to determine stone composition in
addition to assessing stone morphology. The purpose of this study was to
evaluate the role of dual energy CT (DECT) preoperatively to assess the
composition of urinary stones and to compare it with post-operative in vitro
qualitative chemical analysis as reference standard.
METHODS
Forty patients (18 male and 22 female) who presented with symptoms of renal
stones in the department of urology were included in the study. All 40 patients
who were diagnosed to have renal stones clinically and by ultrasonography
(USG) kidney, ureter and bladder (KUB) region were subjected to dual energy
CT. The stone composition assessed in vivo using DECT preoperatively and in
vitro by chemical analysis post operatively after stone extraction by surgical
procedure. The results were compared by statistical analysis. Sensitivity,
specificity and positive predictive value (PPV) were calculated and descriptive
study done using Statistical Package for Social Sciences (SPSS) 20.00 version.
Data was analysed by comparing it with correlative qualitative chemical analysis.
RESULTS
In our study, in vivo analysis using DECT showed most common type of stone
was calcium oxalate seen in 20 cases compromising 50 % of total cases. Next
common stone type was uric acid stone (22.5 %) followed by cysteine (17.5 %)
and calcium hydroxyapatite (10 %) respectively. When the same stones were
subjected to ex vivo chemical analysis, one of the calcium oxalate stone came
out to be calcium phosphate and one of the cysteine stone came out to be mixed
stone. Thus, out of 40 stones, 38 stones were found to have the same result in
ex vivo chemical analysis as that of in vivo analysis by dual energy CT. Hence,
accuracy of dual energy CT in diagnosis of renal stones was found to be 100 %
with CI 91.19 % - 100 %.
CONCLUSIONS
With dual energy CT, it is possible to determine the composition of renal calculi
in vivo non-invasively (with specificity of 100 % in our present study). Therefore,
this helps in deciding the modality of treatment pre-operatively whether the
stone is amenable to medical management (e.g., Uric acid stones) or requires
extracorporeal shock wave lithotripsy (ESWL) or surgical intervention can be
determined preoperatively. This helps to reduce the unnecessary financial
burden and is found to be time saving.
