Helical CT without contrast media as alternative to other methods in urolithiasis

PURPOSE: During the last five years the use of unenhanced helical CT (HTC) has been proposed as a preliminary diagnostic approach in patients with typical renal colics or with nonspecific flank pain. The aim of this study was to describe our experience in this field. MATERIAL AND METHODS: 130 consecutive patients (82 men and 48 women, with an average age of 54 years) were studied; 94 of them presented typical renal colics, while 36 presented acute flank pain. The parameters used were: 5-mm-thick sections, a pitch of 1.6, a reconstruction interscan spacing at 3 mm, an examination area extending from the kidneys to the base of the bladder. Depending on the case, examinations were carried out using urography in the instrumental or surgical pretreatment phase, ultrasonography to check urinary dilatation and juxtavesical calculi, pyeloMR, ureteroscopic extraction, surgical operation, extracorporeal lithotripsy, and finally the expulsion of the calculi was checked. RESULTS: 81 cases of urolithiasis, 6 cases of renal abnormalities and other renal pathologies, 23 cases of extraurinary pathologies correlated to the symptoms, 5 cases of extraurinary pathologies not correlated to the symptoms and 15 normal cases, were diagnosed. The results obtained were a) a sensitivity of 96.8%, a specificity of 98.4% and a diagnostic accuracy of 97.6% in identifying ureteral calculi; b) a diagnostic accuracy of 100% in identifying urinary tract dilatation; c) a sensitivity of 100% and a specificity of 96.7% in determining the level of obstruction; d) a sensitivity of 92.9% and a specificity of 100% in determining the cause of obstruction. CONCLUSIONS: Confirming the data in the medical literature, helical CT has yielded for more reliable results than the other procedures in identifying the following: calculi, acute obstruction of the urinary tract and other urinary and extraurinary pathologies correlated to the symptoms. Therefore helical CT, where available, must be accepted as the method of preliminary evaluation in all patients with typical renal colics or with nonspecific flank pain.     

Spiral computerized tomography without perfusion of contrast media as first line investigation in patients with renal colic

INTRODUCTION: We investigated the diagnostic accuracy of unenhanced helical CT in the detection of stones in patients with suspected renal colic from ureteral stones and compared CT findings with the results of plain abdominal film and US. MATERIAL AND METHODS: We reviewed the findings relative to 80 patients (age range 24-75) who came to our observation to the Emergency Department with acute flank pain. All patients had been examined with plain abdominal radiography, US and unenhanced helical CT. RESULTS: While abdominal radiography showed the presence of radiopaque stones in 38 patients only (47.5%), US demonstrated ureter dilatation in 72 patients and detected stones in 36 of them (45%). Helical CT performed best, depicting a stone in 72 patients (90%), with high sensitivity and specificity. Mean stone size was 3 mm, with 7 mm-1 mm range. The biggest stones were seen in 3 cases and the smallest ones in 34. In 8 patients with no signs of stones we found other extraurinary conditions, namely pancreatitis, diverticula, renal cancer. We also found a case of urinary tract infection. CONCLUSIONS: Thanks to its short execution time and accuracy, helical CT makes the examination of choice in patients with acute flank pain due to renal colic. It is also a most valuable tool in the differential diagnosis of other pathological causes of pain such as abdominal or pelvic masses and inflammatory conditions.     

Sensitivity of CT scout radiography and abdominal radiography for revealing ureteral calculi on helical CT: implications for radiologic follow-up

OBJECTIVE: We compared the sensitivity of CT scout radiography with that of abdominal radiography in revealing ureteral calculi on unenhanced helical CT. MATERIALS AND METHODS: Over a 6-month period, patients presenting to the emergency department with acute flank pain were examined with standard abdominal radiography and unenhanced helical CT, which included CT scout radiography. In 60 patients in whom a diagnosis of ureteral calculus was made, CT scout radiographs and abdominal radiographs were examined by two interpreters who assessed whether stones could be visualized. All CT scout radiographs were viewed on a workstation using optimized window settings. RESULTS: CT scout radiography and abdominal radiography revealed 28 (47%) and 36 (60%) of 60 ureteral calculi, respectively. All ureteral calculi that appeared on CT scout radiography also appeared on abdominal radiography. However, eight calculi that were visible on abdominal radiography were not visible on CT scout radiography. CT scout radiography and abdominal radiography revealed 28% and 46% of 39 calculi less than or equal to 3 mm in diameter, respectively. For 21 calculi larger than 3 mm, the sensitivity of CT scout radiography and abdominal radiography was 81% and 86%, respectively. CONCLUSION: Abdominal radiography is more sensitive than CT scout radiography in revealing ureteral calculi; however, some calculi revealed on unenhanced helical CT cannot be seen on either abdominal radiography or CT scout radiography. Ureteral calculi not visible on either study can only be followed, when necessary, with unenhanced helical CT.     

Combined magnetic resonance urography and targeted helical CT in patients with renal colic: a new approach to reduce delivered dose

PURPOSE: To determine whether magnetic resonance urography (MRU), obtained before helical computed tomography (CT) in patients with acute renal colic, can help delimit the obstructed area to be subsequently examined by a targeted CT scan, thus reducing the dose of radiation. MATERIALS AND METHODS: Patients (51) with symptoms of acute renal colic underwent MRU and a total urinary tract helical CT. CT images from the 5 cm below the level of ureteral obstruction as demonstrated by MRU were selected out. Combined interpretation of MRU and selected CT images constituted protocol A. Protocol B consisted of the entire unenhanced helical CT of the urinary tract. The two protocols were compared regarding the following points: 1) sensitivity in diagnosing the presence of obstructing urinary stones, and 2) the delivered radiation dose. RESULTS: Protocol A and protocol B had, respectively, 98% and 100% sensitivity in demonstrating ureteral stone as a cause of renal colic. Estimated average dose calculated from phantom study was 0.52 mSv for protocol A and 2.83 mSv for protocol B. Therefore, the effective radiation dose was 5.4 times lower in protocol A compared to protocol B. CONCLUSION: Combined MRU and short helical CT has a high sensitivity in detecting ureteral calculi with a reduced radiation dose.     

Suspected ureteral colic: plain film and sonography vs unenhanced helical CT. A prospective study in 66 patients

The aim of this study was to compare the sensitivity and specificity of plain abdominal films plus ultrasound, vs nonenhanced CT for the diagnosis of ureteral colic in patients with acute flank pain. During a 4-month period, 66 patients (mean age 48 years) with acute flank pain were prospectively studied by means of plain abdominal film, US, and unenhanced CT. The presence of lithiasis and of obstructive uropathy signs were determined. The plain film was only used as a guide for the US exam. Clinical follow-up of all patients was obtained. Ureteral lithiasis was confirmed in 56 patients. The CT had a greater sensitivity (93 vs 79%) and negative predictive value (71 vs 46%) for the detection of lithiasis. The combination of lithiasis plus obstructive signs showed a sensitivity and a specificity of 100% for CT and of 100 and 90%, respectively, for US. The 11 lithiasis not detected by US were passed spontaneously (10 were <5 mm). Both techniques showed similar extraurinary pathology. Computed tomography is the most accurate technique for the detection of ureteral lithiasis; however, the combination of plain film and US is an alternative to nonenhanced CT with a lower sensitivity and radiation dose that has a good practical value.     

Ureterolithiasis: classical and atypical findings on unenhanced helical computed tomography

Evaluation of patients with acute flank pain using helical computed tomography (CT) is a well-accepted, rapid, and safe procedure in the emergency setting. Various primary and secondary signs are described in the literature for evaluation of these patients. Our purpose is to demonstrate both the classical findings associated with ureteral calculi on unenhanced helical CT and atypical findings and potential pitfalls. We also provide readers with a systematic approach to interpreting unenhanced helical CT scans performed for acute flank pain. Electronic Publication     

Suspected ureteral colic: primary helical CT versus selective helical CT after unenhanced radiography and sonography.

OBJECTIVE: The purpose of this study was to compare the accuracy of unenhanced helical CT with combined sonography and unenhanced radiography in patients with acute flank pain suggestive of ureteral colic. 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.     

Unenhanced spiral CT for the assessment of renal colic. How does limiting the referral base affect the discovery of additional findings not related to urinary tract calculi?

The value of unenhanced spiral CT (UESCT) for investigating acute flank pain suggestive of urinary tract calculi is increasingly appreciated in the last few years. Recent studies have identified the advantages of UESCT in recognizing alternative findings within or outside the urinary tract. We sought to determine how narrowing the referral base for the UESCT would affect the discovery of potentially significant alternative findings in patients with acute flank pain suggestive of renal colic. Between January 1999 and December 1999, 425 patients, 271 (63.8%) men and 154 (36.2%) women who were 1-90 years old (mean 45.7 years old) with acute flank pain were studied with UESCT. CT studies were solely ordered by urologists, and only patients with intractable renal colic or patients that returned more than once to the emergency room with the complaint of acute flank pain were studied. A calculus within the ureter was diagnostic of an obstructive stone. Any other abnormality within the abdomen and pelvis was reported. A ureteral calculus was detected on 251 (59%) CT scans. Nineteen (4.5%) CT scans were consistent with recent excretion of a stone. In 112 (26.3%) CT scans, the cause for the patient's acute flank pain could not be explained. Forty-three (10.1%) alternative significant diagnoses that explain the patient's complaints were found. Nineteen (44%) were findings related to the urinary tract, and 24 (56%) were not related to the urinary tract. Ninety-seven (22.3%) additional findings not significant to the patient's current complaint were also reported. Even when narrowing the indications for the UESCT, about 10% of significant alternative findings to urinary stones were encountered. The variety of diagnoses found unexpectedly on the UESCT that alter a patient's management demonstrates the pivotal role of UESCT in triaging these patients rapidly towards optimal therapy. The UESCT can be used as a useful screening tool, sometimes revealing the exact pathology and sometimes directing the radiologist to the modality by which to continue.     

Nonenhanced helical CT and US in the emergency evaluation of patients with renal colic: prospective comparison

PURPOSE: To compare nonenhanced helical computed tomography (CT) with ultrasonography (US) for the depiction of urolithiasis. MATERIALS AND METHODS: During 9 months, 45 patients (mean age, 44 years; mean weight, 92.5 kg) prospectively underwent both nonenhanced helical CT (5-mm collimation; pitch of 1.5) and US of the kidneys, ureters, and bladder. US evaluation included a careful search for ureteral calculi. Presence of calculi and obstruction and incidental diagnoses were recorded. Clinical, surgical, and/or imaging follow-up data were obtained in all patients. The McNemar test was used to compare groups. RESULTS: Diagnoses included 23 ureteral calculi and one each of renal cell carcinoma, appendicitis, ureteropelvic junction obstruction, renal subcapsular hematoma, cholelithiasis, medullary calcinosis, and myelolipoma. CT depicted 22 of 23 ureteral calculi (sensitivity, 96%). US depicted 14 of 23 ureteral calculi (sensitivity, 61%). Differences in sensitivity were statistically significant (P: =.02). Specificity for each technique was 100%. When modalities were compared for the detection of any clinically relevant abnormality (eg, unilateral hydronephrosis and/or urolithiasis in patients with an obstructing calculus), sensitivities of US and CT increased to 92% and 100%, respectively. One case of appendicitis was missed at US, whereas medullary calcinosis and myelolipoma were missed at CT. CONCLUSION: Nonenhanced CT has a higher sensitivity for the detection of ureteral calculi compared with US.     

螺旋CT诊断输尿管结石的应用价值（附32例报告）

目的评价螺旋CT对输尿管结石的诊断价值。方法对32例临床表现急性腰腹痛、镜下血尿，可疑输尿管结石的患者，行螺旋CT检查，将获得的容积图像行三维立体重建成像处理。结果31例螺旋CT图像显示出输尿管结石，确诊率97％。8例CT三维立体成像显示结石引起肾盂、输尿管扩张及结石周围组织水肿等继发性变化。结论螺旋CT诊断输尿管结石安全、快捷、准确，有较高的临床应用价值。     

Acute abdominal pain: Is there a potential role for MRI in the setting of the emergency department in a patient with renal calculi?

Acute flank pain is a frequent clinical presentation encountered in emergency departments, and a work-up for obstructive urolithiasis in this setting is a common indication for computed tomography (CT). However, imaging alternatives to CT for the evaluation of renal colic are warranted in some clinical situations, such as younger patients, pregnancy, patients that have undergone multiple prior CT exams and also patients with vague clinical presentations. MRI, although relatively insensitive for the direct detection of urinary calculi, has the ability to detect the secondary effects of obstructive urolithiasis. Using rapid, single shot T2-weighted sequences without and with fat saturation provides an abdominopelvic MR examination that can detect the sequelae of clinically active stone disease, in addition to alternate inflammatory processes that may mimic the symptoms of renal colic. In addition, MR nephro-urography (MRNU) has the ability to provide quantitative analysis of renal function that has the potential to direct clinical management in the setting of obstructing calculi. This review describes the potential utility and limitations of MRI in the emergency setting for diagnosing causes of flank pain and renal colic, particularly in patients with unusual presentations or when an alternative to CT may be warranted.     

Present-day imaging of patients with renal colic

In the past decade alternatives to urography have been proposed for the study of patients with renal colic. In 1992 it was suggested to replace urography with KUB and ultrasonography. In 1993 the combination of KUB and ultrasonography followed by urography in unresolved cases was proposed and, in 1995, it was suggested to replace urography with unenhanced helical CT (UHCT). This article illustrates the contribution of UHCT to the study of patients with renal colic and analyses advantages and shortcomings of the technique compared with other diagnostic approaches. Diagnostics of the patient with renal colic is based on the detection of direct and indirect signs which allow identification of not only the calculus, with a sensitivity of 94–100 % and accuracy of 93–98 % according different authors, but also other signs that can serve to guide patient management and evaluate long-term prognosis. Unenhanced helical CT has the capability to detect extraurinary abnormalities which present with flank pain and mimic renal colic. The examination technique affects the quality of the images and therefore diagnostic accuracy as well as the dose to the patient. With regard to setting parameters, the choice of thickness and table feed should be guided by numerous factors. Multiplanar reconstruction is indicated in the study of the entire ureter course to identify the exact site of the calcification for the urologist to perform an evaluation similar to that obtained by urography. Many authors consider UHCT to be a valuable tool for suggesting the best therapeutic approach. Among these there are also urologists. The evaluation is based on the stone detection, its size and level in the urinary tract. Cost analysis shows that the cost of UHCT is equal to or inferior to the cost of urography. With regard to the dose, different data are reported in the literature. A high pitch (more than 1.5) and a thin collimation (3-mm thickness) are good compromise between quality and dose which can be compared to the dose of normal urography. What is to be done if helical CT is not available? If helical CT is not available, plain film plus ultrasonography should be considered. This approach does not solve all the cases; in unresolved cases urography is indicated. It should also be noted that US has a good sensitivity in detecting other conditions such as biliary lithiasis, acute pancreatitis, acute appendicitis and abdomino-pelvic masses which are responsible for pain that mimics renal colic. In conclusion, IVU should not have any more the priority in investigating the patients with renal colic. Helical CT should be the first choice in imaging a patient with renal colic. If this technique is not available, plain film and ultrasonography should be considered adding urography in unresolved cases.     

低剂量非增强螺旋CT、超声和KUB平片检查在肾绞痛诊断中的前瞻性比较

目的探讨低剂量非增强螺旋CT在急诊肾绞痛中的诊断价值。方法对123例急性腰腹部绞痛而怀疑泌尿系结石患者,根据体质量指数行低剂量非增强螺旋CT检查,并同时行泌尿系超声和KUB平片检查作对照。结果103例确诊为泌尿系结石,其中25例自行排出,45例体外碎石后排出,33例行输尿管镜碎石。低剂量非增强螺旋CT诊断泌尿系结石100例;超声诊断泌尿系结石77例;KUB诊断泌尿系结石68例,5例假阳性。低剂量非增强螺旋CT、超声和KUB的敏感度分别为1Do％、74．8％、66．1％,特异度分别为100％、100％、75％,阳性预测值分别为100％、100％、93．1％,阴性预测值分别为86．9％、43．5％、30．0％,约登指数分别为0．97、0．75、0．41。CT与超声组对比X^2＝21．23,P＝0．000,两种方法差别具有显著性。CT与KUB组对比X^2＝33．04,P＝0．000,两种方法差别具有显著性。结论低剂量非增强螺旋CT诊断泌尿系结石比超声和KUB具有更高的敏感度和特异度,且降低了患者的辐射剂量,可作为临床怀疑泌尿系结石、尤其是急性肾绞痛患者的常规检查方法。     

Normal ureter size on unenhanced helical CT

OBJECTIVE: Unenhanced helical CT is the imaging method of choice when evaluating patients with acute flank pain and suspected ureterolithiasis. In addition to directly identifying stones in the lumen of the ureter, CT secondary signs of obstruction such as ureteral dilatation are frequently present and can be helpful in establishing a diagnosis. The purposes of this study were to define ureteral dilatation on unenhanced helical CT and determine the range of normal ureter size. MATERIALS AND METHODS: We retrospectively reviewed the unenhanced helical CT studies of 212 consecutive patients with acute flank pain whose CT scans showed acute ureterolithiasis. The size of the ureter was determined on the asymptomatic side as well as on the obstructed side. Mean ureteral diameter was determined as the largest transverse dimension along the course of the ureter beginning 1-2 cm below the ureteropelvic junction. RESULTS: The mean size of ureters on the asymptomatic side was 1.8 mm with a standard deviation (SD) of 0.9 mm. The mean size of ureters on the obstructed side was 7 mm with an SD of 3.2 mm. In 96% of patients, the ureter diameter on the asymptomatic side was 3 mm or smaller. CONCLUSION: Three millimeters should be considered the upper limit of normal size for nonobstructed ureters on unenhanced helical CT.     

Abdominal radiography after CT reveals urinary calculi: a method to predict usefulness of abdominal radiography on the basis of size and CT attenuation of calculi

OBJECTIVE: The purpose of this study was to determine if the radiographic visibility of urinary tract calculi could be predicted on the basis of CT features. MATERIALS AND METHODS: The images of 26 patients whose urinary tract calculi were revealed on unenhanced helical CT and who also underwent digital abdominal radiography were retrospectively reviewed. CT features studied included size and CT attenuation of the calculi. These CT findings were correlated with the ability to detect the same calculi with radiography. RESULTS: Forty-nine urinary tract calculi were detected with unenhanced helical CT in 26 patients. Twenty-six (53%) calculi were visible on radiography. Most (79%) calculi larger than 5 mm were detectable with radiography (p < 0.01). One (8%) of 13 calculi with CT attenuation below 200 H was detectable on radiographs. Ninety-five percent (21/22) of calculi with CT attenuation exceeding 300 H were visible on radiographs (p < 0.0001). The one remaining calculus was obscured by overlying anatomy. CONCLUSION: Radiographic surveillance of urinary tract calculi detected with CT may not be useful if the calculi have a CT attenuation below 200 H. Most calculi larger than 5 mm and nearly all calculi with a CT attenuation exceeding 300 H can be seen on abdominal radiographs.     

Non-contrast spiral CT for patients with suspected renal colic

Renal colic, defined as acute flank pain caused by the passage of a ureteral calculus, is a common condition, but the correct diagnosis may not be apparent clinically. For decades, intravenous urography has been the test of choice for evaluating patients with suspected renal colic. Recently, unenhanced (non-contrast) helical CT has been shown to be an accurate and highly effective examination which can be used instead of intravenous urography. In this article, the technique is reviewed in detail, including its advantages and potential pitfalls.     

Acute ureterolithiasis: incidence of secondary signs on unenhanced helical CT and influence on patient management

AIM: The purpose of this study was to determine the incidence of secondary signs associated with ureteral stones on unenhanced helical computed tomography (CT) of patients with acute renal colic, and to correlate these with patient management and outcome. MATERIALS AND METHODS: One hundred and ten patients with ureterolithiasis were evaluated prospectively for the secondary signs of obstruction on unenhanced helical CT. Our attention was focused primarily on the presence or absence of seven secondary signs on unenhanced helical CT, including hydronephrosis, unilateral renal enlargement, perinephric oedema, unilateral absence of the white pyramid, hydroureter, periureteral oedema and lateroconal fascial thickening. RESULTS: Of the 110 patients, 91 (82.7%) had hydroureter, 88 (80%) had hydronephrosis, 65 (59%) had periureteric oedema and 63 (57.2%) had unilateral renal enlargement. Ninety stones passed spontaneously and 21 required intervention. CONCLUSION: Secondary signs of urinary tract obstruction are useful and supportive findings in interpretation of the CT examination. In our experience, the most reliable signs indicating ureteral obstruction are hydroureter, hydronephrosis, periureteral oedema and unilateral renal enlargement, respectively. In addition, stones larger than 6 mm, located within the proximal two thirds of the ureter, and seen associated with five or more the secondary signs of obstruction, are more likely to require endoscopic removal and/or lithotripsy.     

Acute flank pain secondary to urolithiasis: radiologic evaluation and alternate diagnoses

This article discusses the radiologic management of the patient who has acute flank pain. It describes the evolution of radiologic imaging in patients who present with acute symptoms caused by suspected urolithiasis, the advantages of unenhanced helical CT and the limitations of abdominal radiography, intravenous urography, and ultrasonography in this setting, and the alternative diagnoses encountered within the urinary tract, abdomen, and pelvis.     

Radiologic investigation of renal colic: unenhanced helical CT compared with excretory urography.

OBJECTIVE: Our aim was to compare unenhanced helical CT and excretory urography in the assessment of patients with renal colic. SUBJECTS AND METHODS: Fifty-three of 70 consecutive patients with acute signs of renal colic were prospectively examined with unenhanced helical CT, which was followed immediately by excretory urography. Two radiologists who were unaware of the findings independently interpreted these examinations to determine the presence or absence of ureteral obstruction. On all CT scans that had positive findings for ureteral stones or obstruction, we looked for secondary signs of obstruction (perinephric or periureteral fat stranding, ureteral wall edema, ureteral dilatation, and blurring of renal sinus fat). RESULTS: A stone was recovered in 45 of the 53 patients, nine before and 36 after imaging. The latter 36 patients had their stones identified on CT, whereas only 24 patients had their stones identified on excretory urography. Eight patients without stone disease had normal ureters on both CT and excretory urography. Of the 45 patients who had stone disease, 26 had ureteral dilatation on both CT and excretory urography, and 36 patients who recovered a stone after CT had secondary signs of obstruction. Of the nine patients who recovered a stone before CT, three had secondary signs of obstruction. Two patients had periureteral fat stranding, ureteral wall edema, and renal sinus fat blurring. One patient had only ureteral wall edema. CONCLUSION: Compared with excretory urography, unenhanced helical CT is better for identifying ureteral stones in patients with acute ureterolithiasis. Secondary CT signs of obstruction, including renal sinus fat blurring, were frequently present even when the stone was eliminated before imaging.     

CT and MR imaging of neurocysticercosis

OBJECTIVE: The purpose of this study was to evaluate whether unenhanced helical CT of the abdomen and pelvis, supplemented as necessary with delayed enhanced CT of the pelvis, is sufficient for urologists to treat patients with acute renal colic. MATERIALS AND METHODS: CT scans from 99 patients were analyzed retrospectively for the presence, size, and location of ureteral calculi and the presence and severity of secondary signs of obstruction. Clinical follow-up was analyzed by reviewing charts, directly communicating with patients, and reviewing surgical reports. Clinical information was correlated with CT findings. RESULTS: The findings of 51 CT scans were positive for calculi, and the findings of 48 were negative for calculi. The findings from two CT scans were false-positive, and none of the findings were false-negative. The sensitivity, specificity, and accuracy of helical CT were 100%, 96%, and 98%, respectively. A significant difference in stone size was found between patients who were treated conservatively (3.3 +/- 1.3 mm) and patients who underwent a urologic procedure (7 +/- 6.2 mm) (p < .01) and between patients in whom successful ureteral stent placement was the sole intervention (3.9 +/- 2.8 mm) and patients in whom initial stent placement failed and who then underwent a second urologic procedure (7.4 +/- 3 mm) (p < .05). We found no statistically significant difference between the conservatively and interventionally treated groups with respect to stone location. The presence and severity of secondary signs of obstruction were not significantly different between the two groups. CONCLUSION: Stone size alone was found to correlate with patient treatment. Stone location and the presence and severity of secondary signs of obstruction did not affect patient treatment. Because the degree of obstruction and relative renal function are not relevant to the initial treatment of patients with ureteral stone obstruction, CT is adequate for both diagnosis and treatment.