| Abstract|| |
The aim of this study was to find an accurate, easily available and safe imaging modality as an alternative to intravenous urography for the diagnosis of acute urinary obstruction. This retrospective study included 332 patients, who underwent both excretory urography (EU) preceeded by plain radiograph as well as ultrasonography for evaluation of acute flank pain. There were 198 male and 134 female patients. The presence or absence of urinary stones, level of obstruction, excretion delay on EU and dilated excretory system on either or both techniques were recorded. The sensitivity, specificity, predictive values, and accuracy for plain radiograph, ultrasonography, and for both modalities together were measured considering EU as a standard reference. The sensitivity and specificity of combined plain radiograph and ultrasound were 97% and 67%, respectively, with positive and negative predictive values and accuracy rates of 92%, 99%, and 97%, respectively. Our study suggests that the combination of plain radiograph and ultrasonography yields a high sensitivity, negative predictive value, and accuracy in depiction of urinary stones. Thus, EU need not be used as a routine diagnostic procedure in patients with acute obstructive uropathy.
|How to cite this article:|
Samara OA, Haroun DA, Ashour DZ, Tarawneh ES, Haroun AA. Should excretory urography be used as a routine diagnostic procedure in patients with acute ureteric colic: A single center study. Saudi J Kidney Dis Transpl 2011;22:515-20
|How to cite this URL:|
Samara OA, Haroun DA, Ashour DZ, Tarawneh ES, Haroun AA. Should excretory urography be used as a routine diagnostic procedure in patients with acute ureteric colic: A single center study. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2019 Apr 25];22:515-20. Available from: http://www.sjkdt.org/text.asp?2011/22/3/515/80489
| Introduction|| |
Excretory urography (EU) was first introduced in 1923 as a new radiological procedure in the investigation of patients with acute renal colic, and was considered as a gold standard for a long time. More recently, there has been a definite trend toward increased use of unenhanced CT scan (UHCT), and has been considered by many authors as the most informative examination, particularly in patients with small renal or ureteric stones. ,,,,
The lack of availability of CT scan machines in many small radiologic centers and the urgent clinical condition of patients presenting with severe flank pain represent a diagnostic challenge to the emergency department physicians. The diagnosis is usually based on their clinical skill and on the available imaging modalities in any radiology center such as plain radiography kidney, ureter, bladder (KUB) and ultrasound (US). X-ray of the KUB has a sensitivity of 45-60% in the evaluation of acute flank pain; , however, radiolucent stones which nearly represent 10-20% of urinary stones are not visualized.  US is inexpensive, safe and non-invasive procedure, and is more widely available than CT scan; however, its sensitivity in detecting urinary calculi is less than that of UHCT. ,,
This retrospective study was carried out to find an alternative, safe, and easily available imaging modality to EU in the diagnosis of acute renal colic. We analyzed the diagnostic efficiency of combined US and KUB while taking the EU as a standard reference.
| Materials and Methods|| |
Over a period of three years, 332 patients who underwent both EU and US for evaluation of acute flank pain were retrospectively reviewed. There were 198 male and 134 female patients. The mean age of the patients was 46 ± 16 years, with a range of 6-82 years. The presence or absence of urinary stones, the location of the stones and level of obstruction, excretory delay on EU, and dilated excretory system on either or both techniques were recorded.
All the patients were initially evaluated by US and then by EU within a time period ranging from few hours to three weeks. These examinations were performed either by a consultant radiologist or by a senior resident in a teaching hospital. The typical EU protocol in our institution consists of X-ray KUB taken in the prone position followed by intravenous injection of non-ionic iodinated contrast material at a maximum dose of 1.5 mL/kg. A nephrogram image is usually taken at one minute, and then views covering the entire urinary tract in supine position are taken at five minutes, ten minutes and doubling the time if a delayed renal excretion is noted. For X-ray KUB, the prone position was preferred in our institution so as to obtain a natural magnification of a stone based on the concept that the image of an object will be magnified when the object is nearer to the X-ray source. For nephrography, the supine position was preferred as it is more comfortable and the diagnosis of urinary obstruction is usually based on the presence of filling defect in the excretory system or on other well-known secondary signs of urinary obstruction. However, nephrography images were acquired in prone position in some cases to enhance ureteric passage of contrast medium.
US examinations were performed by trans-abdominal approach for all patients on a full urinary bladder, using 3.5 or 5 MHz probes. The kidneys and the urinary bladder were examined in both longitudinal and transverse projections. The course of the ureters was followed down to the urinary bladder with special attention to the uretero-vesical junction. Any focal hyper-echoic focus, with or without posterior shadowing, was considered positive for a stone.
For statistical analysis, the sensitivity, specificity, positive and negative predictive values (PPV and NPV), and accuracy for KUB, US, and for both modalities when conjointly reported were measured considering EU as a standard reference. Cohen's Kappa test was used to define the presence or absence of any correlation between combined KUB and US findings and those on EU. McNemar test was used to identify the presence or absence of a statistically significant difference in the number of stones seen by these tests (significance: P < 0.05).
| Results|| |
One hundred and four of 332 patients (31%) showed urinary stones on EU examination and these represent our study population. There were 81 male patients with a mean age of 48 ± 15 years and 35 female patients with a mean age of 40 ± 16 years. There were 48 patients with stones in the kidney, 36 patients with ureteric stones, 16 patients with stones at the vesico-ureteric junction, and four patients with urinary bladder stones. The stones were in the right urinary tract in 47 cases and on the left side in 57 patients.
X-ray of the KUB demonstrated radio-opaque shadows along the course of the urinary tract in 84 of these patients (81%): 40 cases in projection of the kidneys, 41 along the anatomical ureteric course, and three in projection of urinary bladder. When these stones were compared with the corresponding EU images, urinary stones were confirmed in 81 of the 84 cases; the radio-opaque shadows seen on KUB in three patients were found to be extra-renal in location and were considered to be vascular calcifications. X-ray of the KUB missed urinary stones in 23 cases (22%): ten in the kidney, 12 in the ureters, and one in the urinary bladder; these were considered to be radiolucent stones.
US demonstrated 56 hyper-echoic foci with or without posterior shadowing: 42 (75%) were intra-renal, 12 (21%) were at the ureteric projection and two (4%) were within the urinary bladder. When US and EU findings were compared together, urinary stones as shown on US were confirmed in 45 of 104 (43%) cases: 35 (33%) renal, nine (9%) ureteric, and one (1%) in the urinary bladder, and there were 11 (20%) false-positive cases.
When KUB and US findings were reported conjointly, urinary stones were reported in 101 patients; 51 cases with renal stones, 46 with ureteric stones, and four with urinary bladder stones. Comparison of these findings with the gold standard EU findings revealed that urinary stones were confirmed in 93 cases (89%): 46 (44%), 43 (41%), and four cases (4%) with renal, ureteric, and urinary bladder stones, respectively. There were eight (7%) false-positive cases found on KUB + US; three of these were considered as vascular calcifications and five as hyper-echoic foci misdiagnosed on US as stones.
Both EU and US equally showed dilated ureteric and/or pelvicalyceal (PC) systems: 56 cases (54%) by EU and 55 cases (53%) by US. Delayed renal excretion on EU was observed in 39 cases (38%); of these, US showed dilated PC system in 35 cases and normal system in four cases. There was no renal excretion delay on EU in 65 cases (63%); of these, US demonstrated dilated and normal PC system in 20 and 45 cases, respectively.
The sensitivity, specificity, predictive values, and accuracy of each modality in detecting urinary stones are shown in [Table 1].
|Table 1: Sensitivity, specificity, predictive values and accuracy of X-ray KUB, US and KUB + US in|
detecting urolithiasis in 104 patients.
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Cohen's Kappa test revealed an excellent correlation between the findings of KUB combined with US and the findings on EU (κ = 0.92). In addition, McNemar test did not reveal a statistically significant difference in the number of urinary stones detected by these tests (P = 0.06).
| Discussion|| |
EU is an unsafe radiologic procedure with side effects such as radiation exposure, possible allergic reactions, and nephrotoxicity. In addition, this diagnostic modality has several disadvantages that render its application undesirable. It is time consuming, particularly in patients with delayed renal excretion of contrast material, and the detection rate of radio-opaque stones is 80-90%.  Small ureteric stones can be missed and only indirect signs such as delayed excretion, delayed nephrogram, or dilatation of the excretory system may be observed. The presence of severe obstruction with poor contrast excretion may lead to a sub-optimal direct visualization of the cause of obstruction. ,
In the last few years, many studies have encouraged the use of UHCT as the examination of choice for the detection of ureteric calculi. ,, It was found to be more sensitive than EU in detecting urinary stones and was recommended to replace EU in this clinical condition. ,,,, However, UHCT is expensive and not always available; also, it carries the risk of radiation exposure, particularly in pregnant individuals.
X-ray of the KUB is not useful in patients with radiolucent stones or in those with non-calculus urinary tract obstruction; it also lacks specificity regarding pelvic phleboliths.  The incidence rate of radiolucent stones in our series was 22% and was comparable to other reports.  We did not find it difficult to differentiate phleboliths from ureteric calculi based on their known criteria being rounded, with well-defined outlines, and sometimes by the presence of central lucency. In addition, urinary stones can be missed on X-ray KUB due to overlying fecal material, bowel gas, and osseous structures such as transverse processes of the lumbosacral spine. ,
US has a low sensitivity in detecting urinary calculi; it was found to be less accurate than EU for diagnosis of both obstruction and lithiasis and considered by some authors as a non-invasive alternative diagnostic modality.  Our results show that the sensitivity, specificity, and accuracy of US alone were 48%, 95%, and 82%, respectively, and they were comparable with other published rates. 
It had been reported that US performed by an emergency department physician carried a sensitivity of 72-97% to evaluate hydronephrosis and a specificity of 73% for the detection of urinary stones, compared with EU. , Sheafor et al l showed that the sensitivity of US for direct visualization of ureteric calculi was significantly lower than that of UHCT; it was 61% versus 96%, while in another report, the authors found that both UHCT and US demonstrated a comparable sensitivity and specificity.  In our study, ureteric calculi were undetected on US in 83% of cases; however, when it was reported conjointly with X-ray of the KUB, ureteric calculi were undetected in only 12% of cases and there were three false-positive cases.
Kobayashi et al  found that EU is rarely needed when KUB + US was normal, as stones undetected by these method were usually small and located in the distal ureter and that they may be passed spontaneously.
The essential and most easily detectable finding on US in patients presenting clinically with acute renal colic was dilatation of the urinary tract. Our results demonstrate that both EU and US detected the dilated excretory systems similarly. However, 49 patients (47%) in our study group did not show a dilated PC system on US, although excretion delay on EU was noted in 39 of them. The absence of dilated excretory system in a symptomatic patient can be explained by the absence of sufficient increase in the intra-renal pressure to induce dilatation. Some authors found that a distal ureteric location of the calculi usually produces less hydronephrosis than the proximally located stones.  In our study group, there were 16 cases with distal ureteric calculi without evidence of uretero-hydronephrosis. In addition, there were 29 cases with intra-calyceal location of stones. This observation is important as 59% of symptomatic patients did not show a dilated PC system on US and they could be misdiagnosed as normal. Intra-calyceal calculi may not produce hydronephrosis particularly if they were located in a minor calyx; thus, any hyper-echoic intra-renal focus, in the absence of the classic posterior shadowing, in a symptomatic patient should be carefully reported as this may increase the false-positive rate. In our study, false-positive renal stones were reported in seven cases (17%). According to numerous reports, US is usually unable to differentiate obstructive from non-obstructive dilatation of PC system in the absence of direct visualization of an obstructive agent.
Our results demonstrate that the sensitivity of KUB + US was very high (97%) and the specificity was relatively low (68%), and this is in excellent agreement with other studies where the sensitivity and specificity were 95% and 67%, respectively.  The combined modalities allowed exclusion of urinary tract obstruction in 228 cases (68%). Thus, it is evident that EU is not indicated when these two combined imaging modalities are negative. The combined modalities provided information about the size and location of the calculus, and about the presence or absence of uretero-hydronephrosis. The direct visualization of these abnormalities in a symptomatic patient permits suggesting the diagnosis of acute obstructive uropathy with great confidence. Diagnostic difficulty with these modalities could be encountered in cases with radiolucent stones in the absence of ureteric and/or PC system dilatation. This condition seems to be rare as it was only observed in three of our patients. Several studies found that measuring the intra-renal resistive index by Doppler ultrasonography was helpful in such situations. ,
It had been reported that KUB with abdominal US could be considered as an alternative to UHCT with comparable results. ,, In another study,  the authors suggested that in situations where KUB, US, and UHCT were available, the use of KUB + US is preferable as it is of low cost and less invasive in terms of radiation dose compared to CT scan. Sommer et al  found that UHCT scan was superior to KUB + US for imaging urinary calculi. Many authors recommend utilization of low-dose or ultra low-dose of CT scan. Kim et al  reported that a low-dose CT scan is comparable to standard-dose CT scan for the diagnosis of ureteric stones, which was similar to another report where the authors concluded that their protocol permits reducing the radiation dose up to 95%. 
The primary limitation of the current study was the delay between performing US and EU, which might have resulted in stones previously identified on US and could not be seen on EU since spontaneous passage of small stones is expected. The absence of an absolute standard of truth represents another limitation.
US and plain radiographs are also sub-optimal in obese patients and in those with gassy abdomen that can be secondary to paralytic ileus due to severe colic. In addition, the presence of residual hydronephrosis after passage of calculus in the urine may be non-specific and inconclusive.
However, we found in this study that KUB + US can effectively replace EU and this is in agreement with other reports. ,
| Conclusions|| |
Our study shows that the findings of KUB + US are very similar to those of EU, and we think that our goal was realized irrespective of the real diagnostic accuracy of EU. The combined modalities allowed demonstration of the cause and the level of obstruction in the majority of cases. We strongly believe that EU need not be practiced as a routine diagnostic procedure in patients with acute renal colic.
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Osama A Samara
Consultant Interventional Radiologist, Assistant Professor of Radiology, Jordan University Hospital and Jordan University, P.O. Box 1669, Amman 11953