BJU International (1999), 83, 378–382

Resistive index in renal colic: a prospective studyA.A. SHOKEIR and M. ABDULMAABOUDNew Jeddah Clinic Hospital, Jeddah, Saudi Arabia

Objective To study the role of Doppler ultrasonography −0.001 (0.02), respectively (P<0.001). For all thepatients, RI was sensitive in 77% and specific in 83%,(DU) in the diagnosis of acute unilateral renal

obstruction. and DRI was sensitive in 88% and specific in 98%.Obstructed kidneys showing delayed pelvicalyceal fill-Patients and methods In all, 117 patients with suspected

renal colic were evaluated by intravenous urography ing with excretion of contrast medium (n=42) hadsignificantly higher values of RI and DRI than(IVU) and DU, with determination of the resistive

index (RI) and the diCerence between the RI of ipsilat- obstructed kidneys without delayed filling (n=26).The RI and DRI were more sensitive in the formereral and contralateral kidneys (DRI). RI and DRI were

considered positive with values of �0.70 and �0.06, group. Among patients with obstruction, the RI didnot relate to the time of delay of filling with contrastrespectively. IVU results were considered the ‘gold

standard’ with which renal DU findings were medium, the duration of renal colic or the level ofureteric obstruction.compared.

Results IVU showed both kidneys to be normal in 49 Conclusions Renal DU is a sensitive and highly specifictest that can contribute significantly to the diagnosispatients and unilateral ureteric obstruction with a

normal contralateral kidney in 68. The mean (sd) RI of acute unilateral renal obstruction. It can replacethe IVU, particularly in situations where IVU iswas 0.73 (0.05) in 68 obstructed kidneys, significantly

higher than the mean RI of 0.64 (0.05) in 166 normal undesirable.Keywords Renal obstruction, Doppler ultrasonography,kidneys (P<0.001). The DRI in patients with unilat-

eral obstruction was significantly higher than that in diagnosis, resistive indexpatients with both kidneys normal, at 0.09 (0.05) and

patients were prospectively evaluated using renal ultra-Introduction

sonography (US), followed by IVU. The US studies werecarried out during the attack of loin pain in all patients,Intrarenal Doppler ultrasonography (DU) has been sug-

gested as a possible adjunctive test in distinguishing and before giving any medication in most; in each case,the person performing US was unaware of the findingsobstructed from unobstructed chronically dilated col-

lecting systems [1–4], with the resistive index (RI) being on IVU. The US examination included real-time imagingand intrarenal DU, performed using an Aloka SSD-2000the variable most widely measured. However, there has

been a significant diversity of opinion about the reliability unit (Aloka, Tokyo, Japan) using a transducer frequencyof 3.5 MHz. The degree of pyelocaliectasis was assessedof RI in the diagnosis of acutely obstructed kidneys

[5–12]. Because of the obvious utility of an accurate, in each kidney on the grey-scale images. Pelvicalycealdilatation was subjectively graded as absent, mild, mod-noninvasive method for the diagnosis of acute obstruc-

tion, we carried out a prospective study using DU in the erate, or marked.At least five Doppler spectra were obtained from moreinitial assessment of patients with symptoms suggestive

of renal colic. than three regions in each kidney. Doppler signals wereobtained from arcuate arteries at the corticomedullaryjunctions, interlobar arteries along the border of the

Patients and methodsmedullary pyramids, or both. The Doppler waveformswere made using the lowest pulse repetition frequencyThe study included 117 patients (87 male and 30 female,

mean age 37.8 years, range 16–70) with 234 kidneys possible without aliasing. This maximized the size of theDoppler spectrum and decreased the percentage error inwho presented with unilateral loin pain suspected of

being renal colic. Immediately on presentation, all the measurements. In addition, the lowest possible wallfilter for each ultrasound scanner was used. The Dopplersample width was set at 2–5 mm. The renal RI wasAccepted for publication 13 October 1998

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RESISTIVE INDEX IN RENAL COLIC 379

calculated as: (peak systolic velocity–end diastolic caliectasis, which was considered mild in 33 and moder-ate in three. All 36 obstructed kidneys showingvelocity)/peak systolic velocity, with the RI diCerence

(DRI) determined as the diCerence in RI of the corre- pyelocaliectasis on grey-scale US had an elevated RI.Patients with acute unilateral ureteric obstructionsponding and contralateral kidney. Values of RI and DRI

used for statistical analysis were means of the mean were further classified into two groups, the first compris-ing 42 with delayed pelvicalyceal filling with contrastmeasurements in individual patients.

The IVU was interpreted as negative with a normal medium (suggestive of complete obstruction) and thesecond comprising 26 with no delay in filling (suggestivereno-ureteric unit and positive with hydroureter proxi-

mal to a ureteric stone, with or without delayed pelvi- of partial obstruction). The respective mean (sd) RIs were0.75 (0.06) and 0.70 (0.04), and the respective DRIscalyceal filling with contrast medium. RI and DRI were

considered positive with values of �0.70 and �0.06, were 0.11 (0.04) and 0.07(0.04), both being signifi-cantly higher in the first group (P<0.01, Student’srespectively. The IVU results were considered the ‘gold

standard’ with which DU findings were compared. The t-test). The RI and DRI were more sensitive in the lattergroup; in both groups, DRI was more sensitive and moresensitivity and the specificity of DU values for the diag-

nosis of acute unilateral ureteric obstruction were calcu- specific than RI (Table 2). Examples of DU results inpatients with renal obstruction with delay and no delaylated. DiCerences were assessed using the chi-squared

test and Student’s t-test as appropriate. in filling are given in Fig. 1.In patients with ureteric obstruction, the duration of

pain ranged from 8 h to 4 days and did not correlateResults

significantly with RI. In those showing delayed fillingwith contrast medium, the delay was 10–360 min andIn 49 patients, IVU showed that both kidneys were

normal and the cause of loin pain was confirmed to be was unrelated to RI. The level of obstruction as shownby IVU was proximal in 14, mid-ureteric in 20 and distalnot urological (myositis in 12, radiculitis in eight, appen-

dicitis in five, colitis in seven and biliary colic in 17). In in 34 patients. The mean RI did not diCer significantlyamong patients with various levels of ureteric68 patients, IVU showed evidence of unilateral ureteric

obstruction with a normal contralateral kidney. The obstruction.mean (sd) RI was 0.73 (0.05) in these 68 obstructedkidneys, significantly higher than the mean RI of 0.64

Discussion(0.05) in the 166 normal kidneys (P<0.001). The meanDRI of patients with acute unilateral ureteric obstruction It has been shown in many animal models that acute

obstruction consistently results in local, transient renalwas significantly higher than that for patients in whomboth kidneys were normal, at 0.09 (0.05) and −0.001 vasodilatation followed by vasoconstriction [13,14]. The

renal vasoconstriction is caused by several competing(0.02), respectively (P<0.001). The agreement betweenthe DU and IVU results is shown in Table 1; RI was hormonal factors, the most important of which seems to

be mediated by prostaglandin. It has been suggested thatsensitive in 77% and specific in 83%, while DRI hadbetter diagnostic accuracy, as it was sensitive in 88% the renal vasoconstrictive response that occurs withand specific in 98% of patients. Of the 68 obstructedkidneys, 32 (47%) had no pyelocaliectasis on conven-

Table 2 The accuracy of DU values in the diagnosis of acutelytional US; in 24 such cases, DRI was indicative ofobstructed kidneys with delayed and no delay in pelvicalycealobstruction. The 36 other obstructed kidneys had pyelo-filling with contrast medium

FillingTable 1 The agreement between DU and IVU results in 117patients (234 kidneys) with suspected acute unilateral renal colic

DU Delayed Not delayed P (chi-square)IVU results

Number 42 26Predicted DU results Positive Negative RI

Sensitivity 86 62 <0.05Specificity 83 83RI (no. of kidneys)

Positive 52 29 Overall accuracy 83 80DRINegative 16 137

DRI (no. patients) Sensitivity 95 77 <0.05Specificity 98 98Positive 60 1

Negative 8 48 Overall accuracy 97 91

© 1999 BJU International 83, 378–382

380 A.A. SHOKEIR and M. ABDULMAABOUD

Aa Ab

Ba Bb

Fig. 1. An example of DU in a patient with acute unilateral renal obstruction with A, delayed and B, no delay in pelvicalyceal filling withcontrast medium. In each case (a) shows the contralateral normal kidney (RI=0.604 in A and 0.581 in B) and (b) the correspondingobstructed kidney (RI=0.754, DRI=0.150 in A and RI=0.708, DRI=0.127 in B).

acute complete obstruction is reliably identified by DU contralateral kidneys and with a control group of healthysubjects. Similar results were obtained by Platt et al. [7][5–10].

IVU and grey-scale US are the two most common in 23 patients with acute unilateral ureteric obstruction.However, others reported that DU is highly insensitiveimaging examinations used in patients with acute renal

colic to determine whether renal obstruction is present for detecting acute renal colic [11,12]; Tublin et al. [11]correlated the results of DU with those of urography in[15–17]. Evaluation with US is particularly useful in

conditions when IVU is contraindicated, e.g. pregnancy, 32 patients presenting with symptoms of renal colic.When the published discriminatory thresholds fora history of reaction to contrast material, renal impair-

ment and repeated episodes of renal colic. However, obstruction (mean RI�0.70 and DRI�0.10) wereapplied, the sensitivity and specificity of DU were onlyconventional US is an inaccurate test for obstruction,

because dilatation of the collecting system is often seen 44% and 82%, respectively. This marked discrepancy inthe results could be explained by the diCerence in thein unobstructed kidneys and may not occur or may

occur late in obstructed kidneys. Thus, the present study degree of obstruction. In a recent study, de Toledo et al.[10] investigated the diagnostic accuracy of DU in com-aimed to determine the role of DU in the diagnosis of

acute obstruction. plete as well as partial acute renal obstruction in 64patients. With a threshold RI of �0.70 and ofThe role of renal DU in the evaluation of acute renal

obstruction has been vigorously debated [5–12]. Rodgers DRI�0.06, they showed a sensitivity of 92% in 37patients with complete and 48% in 27 patients withet al. [6] found an elevated RI in acutely obstructed

kidneys, especially when compared with the RI in normal partial obstruction. The present results confirmed those

© 1999 BJU International 83, 378–382

RESISTIVE INDEX IN RENAL COLIC 381

of de Toledo et al.; DU is significantly more sensitive in waveforms barely deviating from the baseline; whenmeasured, these waveforms invariably result in an RIdiagnosing complete renal obstruction than partial

obstruction. that is calculated to lie within the normal range, evenwhen a true state of elevated renal arterial resistanceThe present high sensitivity for DRI of 88% and

specificity of 98% in diagnosing acute renal obstruction is present.The level of ureteric obstruction had no significantmay have arisen because DU was carried out during the

episode of renal colic and before giving any medication impact on the present values of RI, in agreement withPlatt et al. [7]. However, de Toledo et al. [10] havein most patients. Cronan and Tublin [12] discussed the

eCect of NSAIDs in the management of patients with shown that patients with proximal ureteric obstructionhad RIs higher than those with distal obstruction.acute renal colic. These drugs have been shown in

animal models to reverse both the early vasodilatation Previous reports suggest that 17–29% of patients withacute obstruction have abnormalities on DU, despiteand later vasoconstriction that occur with acute renal

obstruction [18,19]. Thus, their use may aCect the normal grey-scale US [6,7]; such abnormalities weredetected in 35% of the present patients. Therefore, whenexpected changes in renal RI; in previous studies, many

patients had received NSAIDs before imaging. The eCect US is used instead of IVU, renal DU is necessary toimprove the sensitivity in early obstruction and to pro-of pharmacological agents on renal RI merits further

study. vide functional information about an obstructed kidney[9].Previous investigators have shown that the increase

in RI occurred after as little as 6 h of clinical obstruction One relative limitation of the present study is thatthere were no cases of acute bilateral obstruction or[7]. This finding is supported by previous laboratory

research that in the earliest stage of obstruction there is acute obstruction of a solitary kidney. However, thepresent results and those of others [6] indicate that suchvasodilatation, with which a normal RI would be

expected [13,14]. However, admission to hospital in the cases are uncommon in clinical practice. Another poten-tial limitation of DU (not found in this study) is thefirst 5 h after the onset of renal colic is uncommon. In

such a situation, although the RI may not be high, a patient with intermittent but very acute renal colic. Ifthe obstruction is present for a few hours only and isDRI of � 0.06 suggests unilateral obstruction before the

RI reaches the 0.70 threshold. We were unable to then relieved, theoretical considerations would suggestthat the RI may not increase, even if this pattern ofinvestigate the shortest duration of acute renal obstruc-

tion that can cause elevation of RI, as all the present intermittent obstruction and relief persists for days [7,9].A third potential limitation of DU is that RI could bepatients presented with renal colic of >7 h duration.

In patients with renal colic for >6 h, conflicting elevated in conditions other than renal obstruction, e.g.chronic hypertension and renal medical diseases.results have been obtained about the eCect of duration

on RI. We agree with Platt et al. [7] that kidneys Therefore, in the setting of known renal medical diseasesand renal colic, an elevated RI could be caused by theobstructed for >12 h do not have a significantly higher

RI than those with obstruction of shorter duration. On renal disease or obstruction, thus limiting the value ofan abnormal RI in this particular situation. The impor-the other hand, de Toledo et al. [10] reported that the

RI was significantly higher in patients with renal colic tance of DRI in such a condition is also unknown.However, a normal RI in this setting would still befor >24 h. These diCerences could be attributable to the

duration of obstruction being based on the clinical helpful in arguing against the presence of obstruction[20].history in all previous studies. The precise duration of

obstruction in patients in a clinical series cannot be In conclusion, DU is a sensitive and highly specifictest that can contribute significantly to the diagnosisascertained.

The application of an adequate DU technique is essen- and management of acute unilateral renal obstruction,particularly in situations in which IVU is undesirable.tial for obtaining accurate results. The most common

reason for obtaining a normal RI in the presence ofsignificant obstruction is a technical error that is simple

Referencesto correct. As described previously, the use of the correct

1 Platt JF, Rubin JM, Ellis JH. Distinction between obstructivescale (pulse-repetition frequency) to expand the wave-and non-obstructive pyelocaliectasis with duplex Doppler

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RJM. Renal Doppler ultrasound in children with obstructivemake this simple technical correction results in minute

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382 A.A. SHOKEIR and M. ABDULMAABOUD

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10 de Toledo LS, Martinez-Berganza-Asensio T, de Cozcolluela- obstructive uropathy. Br J Urol 1997; 80: 195–200Cabrejas R, Gregorio-Ariza MA, Pardina-Cortina P, Ripa-Saldias L. Doppler-duplex ultrasound in renal colic. Eur

AuthorsJ Radiol 1996; 23: 143–811 Tublin ME, Dodd GD, Verdile VP. Acute renal colic: A.A. Shokeir, MD, Associate Professor of Urology.

M. Abdulmaaboud, MD, Associate Professor of Radiodiagnosis.diagnosis with duplex Doppler US. Radiology 1994; 193:697–701 Correspondence: Dr A.A. Shokeir, New Jeddah Clinic Hospital,

PO Box 7692, 21472 Jeddah, Saudi Arabia.12 Cronan JJ, Tublin ME. Role of the resistive index in the

© 1999 BJU International 83, 378–382