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1
Department of Radiology, S. Maria delle Grazie Hospital, Via Domitiana
Località La Schiana, Pozzuoli (Na),
Italy.
2
Present address: Via Crispi 92, Naples, I-80121, Italy.
3
Department of Diagnostic Imaging, PSI Napoli EST, Via Ciccarelli 1, Naples,
I-80147, Italy.
Received May 11, 2001;
accepted after revision August 21, 2001.
Address correspondence to O. Catalano.
Abstract
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SUBJECTS AND METHODS. From January 1997 to December 1999, 181 consecutive patients with acute flank pain underwent unenhanced radiography, sonography, and unenhanced helical CT (protocol A). From January 2000 to December 2000, 96 consecutive patients arriving at the emergency department with acute flank pain were alternately submitted either to primary unenhanced helical CT (protocol B, 48 patients) or to unenhanced radiography and sonography with the addition of helical CT in unclear cases (protocol C, 48 patients).
RESULTS. When compared with the diagnostic accuracy for ureterolithiasis of the combined sonography and radiography in the same group of subjects (protocol A), CT had a greater sensitivity (92% vs 77%), negative predictive value (87% vs 68%), and overall accuracy (94% vs 83%). Among patients who underwent primary CT (protocol B), we found three false-negatives (all with spontaneous stone passage) and no false-positives. Among patients initially examined with unenhanced radiography and sonography (protocol C), we found one false-positive (leading to patient admission and needless repeated radiographic and sonographic studies) and six false-negatives (all followed by an uncomplicated course and spontaneous passage); CT depicted four of these stones but did not result in change in treatment. Fourteen percent of the patients in protocol C required invasive treatment, but combined sonography and radiography showed stones and hydronephrosis in all these patients.
CONCLUSION. Unenhanced CT was the most accurate modality for determining the presence of ureterolithiasis. The combination of abdominal radiography and sonography, however, yielded comparable results with no clinically important misdiagnoses and thus can be used as an alternative when CT resources are limited.
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Nevertheless, in our institutions, as in most others in Europe, urography was replaced long ago by combining unenhanced radiography and sonography. We have had difficulty in convincing our referring clinicians—and ourselves—to perform CT on all subjects with flank pain. Therefore, this study was designed to compare prospectively these diagnostic tools.
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The study was approved by our institutional review board and all patients gave their consent. We selected patients with pain duration of less than 3 days who had unilateral flank pain that could radiate to the abdomen, back, or groin. All patients were evaluated by emergency department general surgeons and none were seen by a urologist before imaging. Some patients were examined after hospitalization, whereas others were first studied in our department and then either admitted or discharged home. Access to the study was possible 24 hr a day, 7 days a week.
Subjects: Protocol A
From January 1997 to December 1999, 181 consecutive patients (108 men and
73 women; age range, 19-73 years; mean age, 40) were imaged because of
suspected ureteral colic. Positive history for renal stone disease or for
previous ureteral colic was present in 36 patients, and microhematuria was
identified in 51.
All patients were submitted first to unenhanced radiography of the urinary
tract, second to sonography, and finally to CT. The interval between the first
and the last study ranged from 5 to 120 min (mean, 
20 min). Radiologists
performing sonography were aware of the radiographic results and used the
radiograph as a guide to focus on suspected areas. The reports of radiographic
plus sonographic findings and the reports of CT findings were written
independently.
Subjects: Protocols B and C
From January 2000 to December 2000, 96 consecutive patients (58 men and 38
women; age range, 22-71 years; mean age, 38) were studied because of suspected
renal colic. A positive history for renal stones or previous colic was present
in 21 patients, and microhematuria was identified in 30.
These patients were alternately randomized in two different protocols. A first group underwent only unenhanced CT imaging (protocol B), whereas another group was imaged with combined unenhanced radiography and sonography, undergoing CT in selected unclear cases (protocol C).
At the end of this 1-year study, 48 patients had been studied with protocol B (28 men and 20 women; age range, 22-62 years; mean age, 41) and 48 patients had been studied with protocol C (29 men and 19 women; age range, 23-71 years; mean age, 37). Among the patients imaged with protocol C, 11 were also studied with CT because of negative or unclear findings on the initial radiographic—sonographic approach; the intervening time from sonography to CT ranged from 10 to 100 min (mean, 15 min).
Imaging Techniques
The technique was the same for all patients who underwent a given
procedure.
Unenhanced urinary tract radiographs were obtained with conventional film or as digital images. A single anteroposterior acquisition of the whole urinary tract was obtained with the patient in supine position. No bowel preparation was used.
Sonographic studies were performed by experienced radiologists using an AU5 or a Technos unit (Esaote Biomedica, Genoa, Italy) and curved phased array transducers, with frequencies ranging from 2.8 to 7 MHz. Most patients were imaged after oral or IV hydration. Subcostal, flank, and back images of both kidneys were first obtained with the patient lying in supine, oblique, and prone positions. Then the dilated proximal and distal ureter or the possible course of the nondilated ureter was followed upward and downward. Finally, the bladder and the ureterovesical junctions were explored with transverse, sagittal, and oblique imaging to detect stones and to analyze the ureterovesical color jets. The ureteral jets were evaluated for about 2 min using a 500-Hz pulse repetition frequency and a 50-Hz filter. In unclear cases of intramural ureteral stone, a direct transperineal approach was also used. No patient underwent transvaginal or transrectal sonographic examination.
The sonographic study was extended to nonurinary structures whenever their involvement was suggested by patient history, laboratory data, or ongoing sonographic findings. A color Doppler sonographic assessment of the kidneys or of any extraurinary structure was added as appropriate.
CT studies were performed by radiologists with at least 5 years of experience with emergency helical CT. All examinations were carried out with a Somatom Plus 4 Expert scanner (Siemens, Erlangen, Germany) with subsecond revolution time (750 msec). The unenhanced images were obtained with the patient in the supine position during breath-hold or breath-hold plus quiet breathing. The volume extended from the superior aspect of the kidneys to the pubic symphysis, using 5-mm collimation, 5- or 7.5-mm/sec table speed (pitch, 0.75 or 1.125), 120 kVp, 180 mA, 3-mm reconstruction interval, soft-tissue image algorithm, and soft-tissue window setting. The CT examinations were interpreted on hard-copy films.
Data Analysis
Because sonography is not well suited for retrospective analysis, we
decided to review only the radiologists' study forms and we did not attempt to
reevaluate the images.
Hydronephrosis was diagnosed on sonography as a separation of the renal sinus polar echoes greater than 5 mm [11] and graded as 1 (central, oval, anechoic area seen in two planes with continuous echoic sinus periphery), 2 (dilated calices connecting to the central area with continuous sinus periphery), or 3 (replacement of most of the renal sinus with discontinuity of sinus periphery) [12].
An abnormal color jet on Doppler sonography was defined as evidence if we found on the side the patient reported pain at least four jets fewer than on the non-obstructed side, a weaker and prolonged jet, a deflected jet (in case of intramural stones), or an absent jet [11, 13,14,15].
We considered the following findings to be positive for ureteral colic: clear calculus image on radiography or sonography, unilateral grade 2-3 hydronephrosis, unilateral grade 1 hydronephrosis plus abnormal ureteral jet, or any combination of these findings [12, 14, 15]. Findings considered uncertain included a suspect stone image on either radiography or sonography, isolated unilateral grade 1 hydronephrosis, and isolated unilateral abnormal ureteral jet.
A CT examination was interpreted as positive when it revealed the following features on the side with pain: stone image (calcified density with the lumen of the urinary tract), unilateral hydroureter plus perinephroureteral stranding or fluid, or any combination of these findings [1, 2, 7, 15, 16]. Findings considered uncertain included a unilateral suspect stone image, unilateral hydronephrosis, or unilateral perinephric or periureteral stranding or fluid.
Uncertain results were counted as a negative outcome of the imaging studies on final data analysis.
Differences between the two techniques were compared by using the chi-square test. A commercially available software package was used (Statistica; Statsoft, Tulsa, OK).
Stones were considered proven when recovered in the urine, extracted during urologic procedures, clearly shown by other imaging modalities, or clearly shown by both CT and sonography with unenhanced radiography [7, 14, 15].
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Eighty-two (51%) of 160 patients had ureteral disease, always unilateral and caused by a single calculus, that was proven by spontaneous stone passage in 60, stone extraction in eight, and other imaging modalities in six (urography in four; ascending pyelography in two). In eight patients, no stone was recovered in the urine, but clear agreement between sonography and CT showed unequivocal evidence of ureterolithiasis. These cases also were considered as confirmed.
A different cause of pain was found in 23 (14%) of 160 patients. Five had ovarian cyst hemorrhage (proven by disappearance of the findings after medical therapy), four had appendicitis (proven at surgery), three had adnexal torsion or ovarian mass torsion (proven at surgery). One patient each had hydrosalpinx (proven at surgery), acute epididymitis (proven by disappearance of the findings after medical therapy), pleuritis (proven at chest radiography), diverticulitis (proven at barium enema), omental infarction (proven by disappearance of the findings after medical therapy), bile duct stone (proven at retrograde cholangiography and sphincterotomy). Also, one patient each had focal pyelonephritis (proven by contrast-enhanced CT and by disappearance of the findings after medical therapy), renal abscess (proven by disappearance of the findings after medical therapy), papillary necrosis (proven at urography), bleeding retroperitoneal sarcoma (proven at surgery), and renal tumor infiltrating the calices (proven at surgery).
No abnormality was found in the 55 remaining patients (34%).
Sonography plus unenhanced radiography was positive in 62 of the 82 patients with ureterolithiasis (Figs. 1A,1B,1C,1D,2A,2B,2C,3A,3B,3C,3D). Sonography was falsely positive in one patient, suggesting a nonobstructing ureteral stone that was excluded at CT and follow-up. In another patient, unenhanced radiography misdiagnosed a vascular calcification as a ureteral stone, as shown on CT images.
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Sonography plus unenhanced radiography showed 19 of 23 cases of alternative cause of pain, including three false-negatives (appendicitis, uncomplicated diverticulitis, and papillary necrosis), one partial false-negative (uncertain result, an ovarian cyst torsion seen but considered as uncomplicated), and two false-positives (cecal mural thickening ruled out at barium enema and coloscopy and diverticulitis shown as diverticulosis on barium enema).
CT findings were positive for ureteral colic in 79 cases with calculi. In another patient, CT suggested a ureteral stone that was proven to be a phlebolith on contrast-enhanced study. CT showed 18 alternative causes, including four false-negatives (acute pyelonephritis, papillary necrosis, pleuritis, and epididymitis), one partial false-negative (uncertain result, a hemorrhagic ovarian cyst considered as uncomplicated), and one false-positive (hemorrhagic adnexal cyst that resulted as a noncomplicated cyst on transvaginal sonography and follow-up).
The sonographic, unenhanced radiography, and CT findings in these 82 patients with ureterolithiasis are listed in Table 2.
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Protocol B
A final diagnosis was available in 40 of 48 patients (22 men and 18 women;
age range, 24-62 years; mean age, 43)
(Table 1).
Twenty-three (57.5%) of 40 patients had ureteral stone disease, proven by stone passage in 17, stone extraction in three, and other imaging modalities in three (urography in two, retrograde pyelography in one).
An alternative cause of pain was found in five (12.5%) of 40 patients, including one appendicitis (proven at surgery), one renal vein thrombosis (proven by contrast-enhanced CT and color Doppler sonography), one renal tumor infiltrating the calices (proven at surgery), and one a ruptured aortic aneurysm (proven at surgery).
No abnormality was found among the 12 remaining patients (30%).
CT allowed correct recognition of stone disease in 20 of 23 patients and alternate causes of pain in four patients. The renal vein thrombosis was not seen on CT images. One false-positive was a case of diverticulosis suggested as diverticulitis.
The single CT findings in the 23 patients with proven stone disease are reported in Table 2.
Protocol C
A confirmed diagnosis was obtained in 39 of 48 patients (22 men and 17
women; age range, 24-70 years; mean age, 40)
(Table 1).
Twenty-one (53.8%) of 39 patients had ureteral stone disease, proven by spontaneous stone emission in 15, stone extraction in three, and urography in three.
An alternative cause of pain was found in three (7.7%) of 39 patients: one with tuboovarian abscess (proven at surgery), one with focal pyelonephritis (proven by contrast-enhanced CT and by disappearance of the findings after medical therapy), and one with bleeding retroperitoneal metastases from lung cancer (proven by contrast-enhanced CT).
No relevant abnormality was identified in the 15 remaining patients (38.5%).
Sonography plus unenhanced radiography was truly positive for ureteral colic in 15 of the 21 patients with ureteral calculi (Figs. 4A,4B,4C and 5A,5B). Unenhanced radiography was falsely positive in another patient, suggesting a stone that was later recognized to be a phlebolith. Sonography showed two of three cases with alternative causes of pain: one was false-negative (hemorrhagic retroperitoneal metastasis) and one was false-positive (appendicitis, ruled out by enhanced CT and follow-up).
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CT was performed in 11 of 22 patients with negative findings on sonographic plus radiographic evaluation. These 11 patients had clinical findings strongly suggestive of ureteral colic. CT depicted a small ureteral stone in four patients, but it failed to show any defined abnormality in the others (Fig. 6).
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The sonography, unenhanced radiography, and CT findings in the 21 patients with a final diagnosis of ureterolithiasis are listed in Table 2.
Diagnostic Accuracy and Impact on Patient Treatment
Compared with the same group of patients (protocol A), the two diagnostic
options (combined sonography and unenhanced radiography vs CT) had,
respectively, a 77.1% and 92.4% sensitivity, a 92.7% and 96.4% specificity, a
95.3% and 98% positive predictive value, a 68% and 86.9% negative predictive
value, and an 82.5% and 93.7% overall diagnostic accuracy. On the basis of
chisquare test results, the calculated value for sensitivity, negative
predictive value, and accuracy was a p value of less than 0.05,
indicating a statistically significant difference. No statistical difference
was found in specificity or positive predictive value.
Sonography plus unenhanced radiography had 20 false-negative results. Nevertheless, all these patients had an uncomplicated course with spontaneous stone emission.
Comparing the effect on patient treatment in two different groups of patients evaluated with the two different algorithms, we found no false-positives in the diagnosis of ureterolithiasis among patients submitted to primary CT (protocol B). The three false-negatives were followed by spontaneous stone expulsion.
Among those patients studied with initial unenhanced radiography plus sonography (protocol C), one false-positive diagnosis for stone disease led to patient admission and to needless repeated radiographic and sonographic studies. Six false-negatives were followed by an uncomplicated course and spontaneous calculus emission in all patients; CT correctly detected four of these calculi, but no relevant change in patient treatment was derived.
In protocol B, three of the patients with stones (13%) underwent urologic treatment and all showed calculi on CT images.
In protocol C, three patients (14.3%) required an invasive treatment. All these showed hydronephrosis at sonography and stones at sonography, unenhanced radiography, or both.
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The limitations of unenhanced CT are few. Interpretation of unenhanced images obtained in patients with acute abdominal pain may be more difficult than evaluation of contrast-enhanced studies. In cases with clear presentation, CT does not increase the diagnostic accuracy. The data provided on exact stone size, shape, attenuation, and location are only partially considered in clinical practice. Finally, limited functional data are obtained with controversial treatment implications [17,18,19].
It is not the accuracy of CT that we debate but its position in the algorithm. We have four main objections to primary CT imaging: radiation exposure, incidence of true-negatives, incidence of spontaneous stone emission, and the availability of alternate techniques.
Concern has been expressed about CT dose [20, 21]. Fielding et al. [7] reported a comparable dosage for CT (4.6 rad [0.046 Gy]) and urography (4.4 rad [0.044 Gy]). Remer et al. [22] calculated a 10- mSv dose from CT, approximately equivalent to that received from three radiographs. Denton et al. [20] estimated an average effective dose of 4.7 mSv, approximately threefold that from three-film urography. Rosser et al. [9] found an effective dose equivalent of 18 mSv. Liu et al. [23] used a low-dose technique and determined an effective dose equivalent of 2.8 mSv, about twofold that from urography. Foley et al. [24] estimated a uterine dose of 0.0036-0.0043 Gy for CT and of 0.006 Gy for standard urography. Exposure may be decreased by using faster table feed [4, 23], subsecond revolution time [22], or lower dose [4]. However, patients are subjected to additional exposure when they undergo scanning in the prone position (to distinguish ureterovesical junction stones from intravesical ones [25]), radiographs as follow-up to CT (to detect stones not evident on the CT scout [26]), a contrast-enhanced study (to assess noncalculous diseases or distinguish distal calculi from phleboliths [6, 14, 16, 24]), urography as follow-up to CT (to distinguish stones from phleboliths or other calcifications [7]), follow-up CT imaging (to monitor stone progression and need for intervention [1, 14, 26]), or when a new colic episode occurs. More than 75% of patients with ureterolithiasis have recurrence [27]. A selective use of CT would reduce overall population dose.
Many CT examinations reveal negative findings for ureterolithiasis and for alternative causes or show signs of recent passage. In our series, 34% of the patients had true-negative findings. Among the major series [2, 3, 7, 8, 10, 14, 17, 18, 20, 23, 27, 28], the rate of true-negative findings ranges from 16% to 62% of patients, which represents, in mean, approximately half the subjects investigated. With increasing clinician familiarity with this technique, the number of examinations with negative findings may increase: Chen et al. [29] compared 2 years of experience and reported that stones were found in 49% of the patients imaged in the first year and in 28% of those evaluated in the second year. Moreover, in all series [2, 14, 18, 26] there are several patients who were lost to follow-up or who lack a final diagnosis (14% in our experience), and many of these cases are believed not to be due to ureteral colic or to be related to irrelevant forms of ureterolithiasis [18].
Most patients with ureteral colic recover spontaneously [2, 11, 14, 18, 26]; assessing precisely the stone size and location and the presence and severity of the accessory findings in these patients has a limited practical value.
Finally other methods are available to screen patients with flank pain. In our experience, sonography combined with unenhanced radiography proved a valuable alternative to CT. In comparing the diagnostic accuracy of the various modalities in the same patients (protocol A), we found CT more accurate than combined sonography and unenhanced radiography in diagnosing ureteral colic. Nevertheless, all of our patients whose stones were incorrectly classified recovered spontaneously. Hence, the positive CT result in these patients had a limited practical value. The observation that false-negatives on sonography are usually followed by spontaneous stone emission has been already reported [11], and we believe that finding represents a key point in focusing this argument. When we compared the results of the imaging modalities carried out in different patient populations, we observed that treatment was effective both in patients studied with primary CT (protocol B) and in patients with initial sonographic and radiographic imaging (protocol C). Again, patients with a false-positive finding with the sonography-and-radiography approach had an uncomplicated course, whether CT revealed negative or positive findings.
Misconceptions about sonography are common. Many articles [5, 24, 30] state that calculi cannot usually be seen on sonography and, hence, that this technique is not efficient in the detection of ureteral colic, but this opinion is confuted by recent studies [31, 32]. Most stones are located within the upper ureteral third or at the ureterovesical junction, and a careful search allows detection of most of them [31]. Also, it has been shown that, in the proper setting, detection of unilateral hydronephrosis is suggestive of acute obstruction with few false-positives [11, 12]. Sonography cannot be separated from the unenhanced radiographic findings that provide increased ability to explore the entire ureter: articles find that unenhanced radiography has a 59-66% sensitivity for calculi [11, 26, 27], mainly missing stones smaller than 3 mm. With the use of combined sonography and unenhanced radiography, a sensitivity of 80-97%, a specificity of 59-67%, and a negative predictive value of 92-95% have been reported [31, 32]. Finally, many researchers use renal-limited sonography and do not attempt to evaluate the entire urinary tract or to use tools such as ureteral color-jet assessment or intrarenal resistive index measurement [22, 28, 30, 33]. Some patients in our institutions are also studied by using pulsed Doppler sonography to assess resistive index changes: we use this technique when other results are indeterminate, but this modality has raised controversies and is time-consuming [11, 13]. Unenhanced radiography combined with complete sonography (including jet assessment and resistive index measurement) has shown an 84-97% sensitivity and an 85-100% specificity [11, 13].
A comparison between sonography and CT is reported in three articles [14, 15, 28]. In one study of 16 patients with documented stones, sonography had an 81% sensitivity and CT a 100% sensitivity with, respectively, 12.5% and 94% of calculi directly detected [15]. Sonographic results are not correlated with those of routinely performed unenhanced radiography. In another experience, sonography and CT showed a 19% and a 94% sensitivity in detecting ureteral stones, respectively [14]. Nevertheless, although sonography shows caliceal dilatation in 73% and abnormal ureteral jet in 53% of patients with stones, these data are not considered, and the additional value of routinely performed unenhanced radiography is not analyzed. Sheafor et al. [28] also focused on calculus detection, and they reported a sensitivity of 61% for sonography performed by sonographers and 96% for CT. When the two techniques were compared for overall "detection of clinically relevant abnormalities," sonographic sensitivity increased to 85% and CT sensitivity to 100%. In the study by Sheafor et al., three positive findings (13%) were missed on sonography; unenhanced radiography was not performed.
Our series is larger than others and compares CT with combined sonography and unenhanced radiography from all points of view. Although less accurate than unenhanced CT, sonography with unenhanced radiography allows detection of all clinically relevant cases with similar consequences for decision-making and patient treatment. In particular, in our experience, all patients whose stones were missed at sonography plus radiography recovered spontaneously.
CT and sonography also have a comparable accuracy in diagnosing alternative causes of pain, which is considered a major advantage of CT over urography. In one series, only one patient with an alternative CT diagnosis (appendicitis) was reported; the sonographic findings in this patient were not reported [15]. In another study, a single case of alternative cause (appendicitis) was reported as having been detected by CT and missed on sonography [28]. Yilmaz et al. [14] found CT more accurate in recognizing mimickers of ureteral colic, because this technique identified six of seven alternative causes, whereas sonography recognized only four of them. In our series, the overall number of alternate causes is limited, probably as a result of better clinical selection. However, our series is larger that those previously mentioned and shows that sonography is as accurate as CT in diagnosing causes other than ureterolithiasis.
Finally, two other factors must be considered: time consumption and financial cost. In one study, the average time for CT, including reformatted images, was 15 min, whereas that of sonography plus unenhanced radiography (frequently including one or both oblique views) was 37 min [22]. Another article reported that the complete CT study took 10-15 min, whereas sonography, including jets assessment, required 35-40 min [28]. Yilmaz et al. [14] found that the examination time for CT was approximately 5 min, whereas that of sonography was slightly longer. We did not precisely calculate the examination time, but, in our experience, the CT studies took approximately 10 min, whereas unenhanced radiography and sonography lasted for about 20 min. The overall efficiency of performing sonography and unenhanced radiography versus unenhanced CT depends partially on the relative resources within the emergency department and the expertise of the radiologists. Examination time will affect the most efficient use of radiologist's time.
In most institutions, the financial charge for unenhanced helical CT has been made equal to or even lower than that for urography [1, 5, 15, 16]. From the clinician's point of view, Li et al. [34] found CT expensive: the CT diagnosis resulted in a $1,409 charge with a $673 maximal insurance reimbursement, and the urographic diagnosis resulted in a $445 charge with a $141 maximal reimbursement. Remer et al. [22] estimated that the technical cost of helical CT is $37 compared with $58 for sonography plus unenhanced radiography, although we believe that is probably an underestimate of the true CT costs. Grisi et al. [35] found that the full cost of primary CT was 74 Euro ($71), which was higher than that of sonography plus unenhanced radiography plus selective CT (64 Euro [$62]).
A minor methodologic limitation of our study should be highlighted. In all protocols, and especially in the patients included in protocol A, the order of performance of the imaging studies should have been randomized to avoid changes such as stone passage. Nevertheless, the interval time between radiography, sonography, and CT was limited, and no patient passed stones in the meantime.
Because of the good negative predictive value of sonography plus unenhanced radiography, CT is rarely helpful in patients with an initial negative result, mainly detecting minor, spontaneously resolving colic caused by tiny stones. In our experience, a sonographic—radiographic approach is accurate in assessing most patients, although it should be stressed that CT allows a more constant and precise depiction of stone size, which is relevant information in predicting spontaneous passage [17].
We suggest two paths: performing a CT study in all patients with negative sonographic—radiographic results (expecting to have various negative results and various positive results because of minor colic), or performing a CT examination only when the referring clinician has a strong conviction that the patient may have major colic or a relevant nonureterolithiasic cause of pain (for example, patients without hematuria). We believe that CT should be used mainly when the initial workup is equivocal for both ureteral obstruction and alternative causes or when urologic intervention is believed necessary. In our protocol C, however, a conspicuous number of patients with initial radiographic—sonographic approach underwent CT imaging (50% of those with negative initial workup and 23 of the total) and, hence, patient selection remains a problem.
Smith and Varanelli [6] recently stated that "at least in relation to stone disease unenhanced helical CT is truth." We agree, but we believe that unenhanced radiography plus sonography is near truth, which in most patients is enough. An approach using urinary tract radiographs plus full-potential sonography may obviate CT in the majority of patients: the combined modalities will mainly miss colic caused by 1- to 3-mm stones, and the patients will usually recover with conservative treatment. Primary CT causes an overevaluation of these patients with minor colic. Selective CT decreases overall dose and cost, at the price of a slight increase in the time necessary to reach diagnosis. Both diagnostic accuracy and patient treatment will be unchanged.
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