British Journal of Radiology 75 (2002),351-355 © 2002 The British Institute of Radiology
Colour Doppler evaluation of ureteral jets in normal second and third trimester pregnancy: effect of patient position
N Karabulut, MD1 and
A Karabulut, MD2
1 Department of Radiology, Pamukkale University Hospital, 20010, Denizli and 2 Clinic of Obstetrics and Gynaecology, Denizli State Hospital, 20010, Denizli, Turkey
Correspondence: Nevzat Karabulut, MD, Hastane Cad., Umut Apt. 5/3, 20010 Denizli, Turkey
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Abstract
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The study was designed to investigate the effect of patient position on the detection of ureteral jets in normal pregnancy. The number of jets was recorded for 1 min using colour Doppler ultrasound in 26 healthy asymptomatic gravid women between 16 weeks and 34 weeks gestation. Each patient was examined in the supine position and in both the right and left lateral decubitus positions. Ureteral jets were present on at least one side in 24 patients in the supine position compared with 26 women in the lateral decubitus position. 13 (54%) of the 24 patients in whom jets were seen in the supine position had jets on only one side. A mean of 1.80 jets min-1 was detected on the right side and 3.23 jets min-1 on the left (p=0.046) in the supine position. In the contralateral decubitus position, jets were detected on the right side in 22 (85%) women and on the left in 25 (96%) women. A mean of 3.07 jets min-1 was detected on the right and 4.15 jets min-1 on the left. The difference in the frequency of ureteral jets between the supine and lateral decubitus positions was significant (p=0.004 for the right; p=0.011 for the left). However, the difference in the detection rate was significant on only the right side (p=0.016 for the right; p=0.063 for the left). 10 (77%) of 13 patients in whom unilateral absence of ureteral jets was noted had detectable jets in the lateral decubitus position. Our findings demonstrated the utility of the lateral decubitus position in the evaluation of ureters suspicious for obstruction. However, caution is still recommended in diagnosing ureteral obstruction if jets are persistently absent after this manoeuvre.
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Introduction
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Renal colic is the most common painful non-obstetric condition for which hospitalization is required during pregnancy, and urolithiasis is estimated to complicate between 1 in 188 and 1 in 3821 pregnancies [1–3]. Ultrasound is frequently requested as the initial imaging study for the evaluation of renal colic in pregnant women. Nevertheless, pregnancy-related calyceal dilatation limits the specificity of ultrasound for the detection of obstruction [3].
Colour Doppler ultrasound evaluation of ureteral jets is a useful adjunct to grey-scale ultrasound in the diagnosis of ureteral obstruction [4] and has also been found to be helpful in pregnant women, when there is negligible risk to the fetus [5]. Asymmetry of ureteral jets, manifesting as absence of flow or sluggish continuous flow from the affected side, implies ureteral calculi [4, 6, 7]. However, colour Doppler ultrasound findings in asymptomatic pregnant women may simulate the appearance of high grade ureteral obstruction due to diminished smooth muscle tone in the ureter and extrinsic ureteral compression by the gravid uterus. The frequency of unilaterally absent ureteral jets has been reported to range from 3.2% to 15.3% in this population [5, 8, 9]. It is possible that ureteral compression may be relieved in the lateral decubitus position. Indeed, Wachsberg [8] reported that unilateral absence of jets in the supine position should not be interpreted as a sign of obstruction unless it persists in the contralateral decubitus position. To further investigate this phenomenon, a prospective study was undertaken in healthy asymptomatic pregnant women in the second and third trimesters of gestation.
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Materials and methods
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The study population was drawn from patients undergoing routine obstetric ultrasound examination. A total of 26 women who denied a history of urinary obstruction or previous urological surgery and in whom renal ultrasound excluded evidence for solitary kidney, renal scarring, nephrolithiasis and 1.5 cm or larger size discrepancy in the long axis were prospectively enrolled in this study. Informed consent was obtained from each participant after a detailed explanation of the procedure. All women (age range 17–36 years, mean 25.5 years) had singleton pregnancies between 16–34 weeks gestation (mean 25.7 weeks).
Before colour Doppler ultrasound, each subject was asked to drink 1000 ml of water and to report when a persistent sensation of bladder fullness was present. Initially, each kidney was scanned to assess collecting system dilatation. The degree of hydronephrosis was graded on a scale from 0–3 according to the method of Peake et al [10] in which grades 0–3 denote increasing degrees of sinus echo separation. Then, with the subject in a supine position, colour Doppler ultrasound of the distended bladder was carried out in the transverse plane to include both ureteral orifices for simultaneous visualization of jets on both sides. Caution was taken not to include the fetus in the field of view. The ureteral jets were visualized at the level of the trigone of the urinary bladder as a line of colour signals emanating from a ureteral orifice, oriented in an anteromedial direction, with flow toward the transducer. All examinations were performed by the same radiologist using a commercially available colour Doppler scanner (Logic 500 Pro; General Electric, Milwaukee, WI) with a 2.0–5.0 MHz convex probe. The colour scale was adjusted as needed, and flow toward the transducer was assigned a red colour. Colour gain was set just below the level at which noise was seen. A wide sample gate was applied to cover the ureteral jet.
Because it is unusual for jets to appear after they have not been detected on either side during 1 min of real-time colour Doppler ultrasound [8], continuous scanning was performed and the number of ureteral jets was counted for 1 min. If no jets were detected at either ureteral orifice in 1 min, scanning was continued for 3 min. Each patient was then asked to assume the right and left lateral decubitus positions, and the frequency of ureteral jets on colour Doppler ultrasound was recorded as above for 1 min or 3 min. Right ureteral jets were recorded in the left lateral decubitus position and left ureteral jets were recorded in the right lateral decubitus position. Ureteral jet flow velocities were not measured, and Doppler ultrasound of the kidney was not performed.
Statistical analysis was performed with the Statistical Package for Social Sciences computer program version 9.0 (SPSS Inc., Chicago, IL). The Mann–Whitney U-test was used to analyse differences between the degree of hydronephrosis in each kidney, and between the number of ureteral jets at each orifice. Correlation between the grade of hydronephrosis and ureteral jet frequency was investigated using the Pearson correlation test. The Wilcoxon signed ranks test was employed to assess differences in the frequency of ureteral jets, and the McNemar test was used to investigate differences in the detectability (presence or absence) of ureteral jets recorded in the same patient in two different examination positions (supine vs lateral decubitus). p-values less than or equal to 0.05 indicated a statistically significant difference.
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Results
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Collecting system dilatation was encountered more frequently and was more severe on the right side than on the left. The mean degree of collecting system dilatation was 0.96 for the right side vs 0.5 for the left side (p=0.019). There were no cases of severe or high grade physiological hydronephrosis. There was no significant correlation between the number of jets and the grade of hydronephrosis (p=0.427 on the right, p=0.112 on the left).
Ureteral jets were detected on at least one side in 24 women in the supine position compared with 26 women in the lateral decubitus position. In the two patients (25 and 35 weeks gestation) who did not have detectable ureteral jets on either side of the ureteric orifice in the supine position, this absence of jets persisted on the right ureteric orifice when they were placed in the lateral decubitus position, but one jet in one woman and three jets in the other woman were seen on the left side after a minute. 11 (46%) of the 24 patients in whom jets were seen in the supine position had bilateral jets, whereas 13 (54%) patients had jets on only one side; jets were absent on the right side in nine patients and on the left in four patients (Figure 1a
). The mean degree of collecting system dilatation in the 13 patients with asymmetric jets was 0.77 (grade 0 in six patients, grade 1 in four patients and grade 2 in three patients). The total number of jets per minute ranged from 0 jets min-1 to 7 jets min-1 (mean 1.80 jets min-1) on the right side and from 0 jets min-1 to 10 jets min-1 (mean 3.23 jets min-1) on the left (p=0.046). The number of jets on the left side exceeded those on the right in 15 (58%) subjects; the number of jets was higher on the right side in 7 (27%) subjects.
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Figure 1. 24-year-old asymptomatic woman at 29 weeks singleton gestation. (a) Transverse colour Doppler ultrasound in the supine position reveals a ureteral a jet emanating from the left ureteral orifice. No jet was seen on the right, suggesting ureteral obstruction. (b) A normal right ureteral jet is depicted after the patient assumed the left lateral decubitus position, excluding true ureteral obstruction.
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All patients had detectable jets on at least one side in the contralateral decubitus position. Jets were detected on the right side in 22 (85%) women and on the left in 25 (96%) women. The total number of jets per minute ranged from 0 jets min-1 to 8 jets min-1 (mean 3.07 jets min-1) on the right side and from 0 jets min-1 to 12 jets min-1 (mean 4.15 jets min-1) on the left (p=0.235). The difference in the frequency of ureteral jets between the supine and lateral decubitus positions was significant (p=0.004 for the right, p=0.011 for the left). Compared with supine position, the number of jets per minute increased in 7 cases on the right vs 10 cases on the left in the lateral decubitus position; it decreased in two patients on the right vs five patients on the left; and it remained unchanged in six patients on the right vs five cases on the left.
However, the detectability (absence or presence) of ureteral jets was statistically different on only the right side (p=0.016 for the right; p=0.063 for the left). 7 (78%) of 9 patients with absent ureteral jets on the right in the supine position had detectable jets in the left decubitus position (Figure 1b
). Similarly, 3 (75%) of 4 patients who did not have jets on the left in the supine position showed ureteral jets when examined in the right lateral decubitus position. In no case was an absent jet observed in the lateral decubitus position when it had been present in the supine position (Table 1). No subjects demonstrated low level continuous flow, a finding that has been reported in some patients with partial obstruction.
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Table 1. Detectability of ureteral jets in the supine and lateral decubitus positions at 52 ureteric orifices in 26 patients
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Discussion
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Colour Doppler ultrasound detection of ureteral jets reflects urine flow from the ureteral orifice. Therefore, unilateral ureteral obstruction may be suggested in the presence of unilateral absence of jets or trickling flow [4]. However, a physiological decrease in ureteral smooth muscle tone as well as extrinsic compression of the ureters by the gravid uterus may simulate high grade ureteral obstruction and thus cause erroneous diagnosis in some women during pregnancy. As the growing uterus emerges from the pelvis, it compresses the ureters as they cross the pelvic brim. This obstruction is more pronounced on the right side than on the left (85% vs 15%), primarily owing to dextrarotation of the uterus [11, 12].
In our study, the degree of calyceal dilatation was more marked on the right side than on the left. However, there was no statistically significant correlation between the degree of hydronephrosis and mean jet frequency. This finding corroborates previous studies reporting that gestational hydronephrosis is seen early in pregnancy and is more prominent on the right side [5, 10]. This study also demonstrated that the difference in the mean frequency of the right vs left ureteral jets was statistically significant in the supine position but not in the lateral decubitus position. In a series of 125 healthy asymptomatic gravid women, Asrat et al [5] reported that the frequency and symmetry of ureteral jets were not affected in pregnancy, thus they could be used in the work-up of suspected urolithiasis in pregnant patients. On the contrary, Burke and Washowich [9] reported that variation occurred in jet bilaterality and symmetry during the later stages of pregnancy and caution is thus recommended in the use of the colour Doppler technique to diagnose urolithiasis in the pregnant population.
In this study a relatively high percentage (54%) of unilaterally absent jets was observed in the supine position. The prevalence of unilaterally absent ureteral jet has been reported to range from 3% to 15% in other studies performed in healthy pregnant subjects [5, 8, 9]. In a recent study by Chiu et al [13], ureteral jets were absent on one side of the orifice in 6 (40%) of 15 non-pregnant patients with a wide range of renal dysfunction despite well visualized jets on the contralateral side. The shorter scanning time used in our study might have caused a comparatively higher proportion of unilaterally absent jets in the supine position. Although there is no well established examination time for the evaluation of ureteral jets, most previous studies [4, 5, 9] have used 5 min scanning time, and Cox et al [6] reported that at least 30 min of colour Doppler ultrasound is necessary to document that asymmetry of jet frequency is a true finding. Because the period between jets was reported to range from 2 s to 45 s in most patients [6], the pregnant volunteers in this series were not asked to undergo prolonged examination. The maximum examination time was 3 min, which was sufficient to assess the findings that are clearly diagnostic of high grade obstruction.
Wachsberg [8] reported that jets were detected in the lateral decubitus position in each subject who had a unilaterally absent jet in the supine position. He concluded that a unilaterally absent jet seen in the third trimester of pregnancy should not be interpreted as a sign of obstruction unless it persists in the contralateral decubitus position. In our study, significant increases were observed in mean jet frequency on both sides, and in the detection rate (presence) on the right side when subjects assumed the lateral decubitus position. Moreover, the percentage of detectable jets was much higher in the contralateral decubitus position than in the supine position. Most of the subjects who did not have detectable jets in the supine position demonstrated ureteral jets in the contralateral decubitus position, similar to the series of Wachsberg [8]. This finding is most likely owing to the fact that extrinsic compression of the ureter by the gravid uterus in the supine position was relieved in the lateral decubitus position. However, in three patients with absent unilateral jets in the supine position, the finding persisted in the lateral decubitus position, although the patients were completely asymptomatic. This might have resulted from the relatively short period of scanning in our study. The lack of difference in urine density between the ureter and the bladder may also have caused ureteral jets to go undetected. Because we did not allow the volunteers to void and refill the bladder before the examination, the lack of relative specific gravity between ureteral urine and urine in the bladder would be negligible, thus it is not deemed to have a role in the absence of jets.
In conclusion, colour Doppler imaging of ureteral jets offers potentially useful information in the assessment of urolithiasis. Nevertheless, urine flow may be altered in pregnancy, simulating ureteral obstruction in some women imaged in the supine position during the second and third trimester of pregnancy. Examination in the lateral decubitus position eliminates the extrinsic ureteral compression by the enlarging uterus and may be a useful manoeuvre in most patients in the evaluation of the suspicious ureter. However, caution is still recommended if jets are persistently absent after this manoeuvre, as this may still occur in some healthy subjects. Prolonged scanning time in this population may potentially reduce the false positive results.
Received for publication September 5, 2001.
Revision received December 7, 2001.
Accepted for publication December 21, 2001.
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Abstract
Introduction
