Central Journal of Urology and Research

Cite this article: Kumar R, Kundu J (2015) Prospective Comparison of Unenhanced Spiral Computed Tomography with Intravenous Urography and Combina-tion of CT Scout with Ultrasound in the Evaluation of Acute Renal Colic. J Urol Res 2(2): 1024.

*Corresponding authorRavinder Kumar, AG-1, Geetanjali Medical Campus, Manvakhera, Udaipur-313002, Rajasthan, India, Tel: 09571218953; Email:

Submitted: 03 March 2015

Accepted: 21 April 2015

Published: 22 April 2015

Copyright© 2015 Kumar et al.

OPEN ACCESS

Keywords•CT Scout view•IVU•NCCT•Ultrasound and ureteric calculus

Research Article

Prospective Comparison of Unenhanced Spiral Computed Tomography with Intravenous Urography and Combination of CT Scout with Ultrasound in the Evaluation of Acute Renal ColicRavinder Kumar1* and Jyoti Kundu2

1Department of Radio-Diagnosis, Geetanjali Medical College & Hospital/ Geetanjali University, India2Department of Prosthodontics, Geetanjali Dental & Research Institute/ Geetanjali University, India

Abstract

Objective: 1) Prospective comparison of unenhanced spiral computed tomography (NCCT) with Intravenous Urography (IVU) and Combination of CT scout with Ultrasound (CT+US) in the Evaluation of acute renal colic.

2) To formulate a model for predicting the probability of the presence of ureterolithiasis while simultaneously assessing the effects of Body Mass Index (BMI), Size of calculi, Hydronephrosis and Imaging appearance of calculi in ureterolithiasis diagnosis.

Subjects & Procedure: After giving informed consent, 100 adult patients with acute renal colic suspected of having urolithiasis underwent NCCT, IVU & CT+US. The diagnosis of ureterolithiasis was confirmed during follow-up either from direct stone recovery or urological interventions. Observations were made by two radiologists independently, unaware of the findings, in consensus reviewed and interpreted all images to determine the presence or absence of ureteral calculi. Sensitivity, specificity and positive predictive values for detecting ureteral calculi were determined and the effects of above mentioned factors were analyzed with Multivariate logistic regression model.

Results: Per-patient sensitivity, specificity, positive predictive value, negative predictive value and accuracy for detecting ureteral calculi with NCCT (100% [80/80], 90% [18/20], 97.5% [80/82], 100% [18/18] and 98% [98/100] respectively) were significantly greater than those for IVU (97.2% [70/72], 57.1% [16/28], 85.3% [70/82], 88.8% [16/18] and 86% [86/100]) & combination of CT scout with Ultrasound examinations (92.5% [74/80], 60% [12/20], 90.2% [74/82], 66.6% [12/18] and 86% [86/100]) (p=0.000). Body Mass Index, Size of calculi, Hydronephrosis and Imaging appearance of calculi, were significant univariate predictors in diagnosing ureterolithiasis.

Conclusion: NCCT remains the gold standard in initial imaging however its prudent to use a combination of CT scout + US in follow-up imaging due to minimal radiation exposure and significantly reduced cost.

INTRODUCTIONRenal colic may be suspected based on the history and

physical examination, but diagnostic imaging is essential to confirm or exclude the presence of urinary calculi. Several imaging modalities are available, and each has advantages and limitations.

Previous studies [1-3] showed Non-Contrast spiral Computed Tomography (NCCT) as the most sensitive and specific diagnostic modality for detecting urolithiasis. Consequently, NCCT is frequently used in the initial diagnosis of urolithiasis and in the follow-up of known ureteral calculi before and after treatment [4]. Nevertheless, there are a number of potential pitfalls in the

interpretation of unenhanced helical CT, the major one being the differentiation of a distal ureteral stone from a phlebolith [3]. A valid surveillance protocol for the management of ureterolithiasis is essential because of the increased cost of high-resolution axial imaging modalities and potentially harmful cumulative effects of radiation dosage. However, the critical question about which imaging technology should be employed in a given clinical scenario remain unanswered. The aim of our prospective study was not only to comparatively evaluate the performance of unenhanced helical CT, intravenous urography and combination of CT scout with ultrasound in the detection of ureteral stones in a relatively large group of patients who presented with acute clinical signs of renal colic. But in addition, we tried to identify

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additional factors, such as Body Mass Index (BMI), Size of calculi, Hydronephrosis and Imaging appearance of calculi, as significant univariate factors in predicting the probability of the presence of ureteral calculi in patients with positive radiodiagnostic examinations by the above said imaging modalities.

Subjects and procedure

Patients: Institutional review board approval for performing NCCT, IVU and combination of CT scout with US, viewing images and medical records of patients, with sign and symptoms of renal colic, was obtained before initiation of this study, which was compliant with Health Insurance Portability and Accountability Act (HIPAA). The diagnosis of ureterolithiasis was confirmed during follow-up either from direct stone recovery or urological interventions including Medical Expulsive Therapy (MET) to facilitate spontaneous stone passage, percutaneous antegrade ureteroscopy, and laparoscopic and open surgical ureterolithotomy. Eighty two of hundred patients evaluated were diagnosed with ureterolithiasis. Medical records of patients undergoing 100 consecutive NCCT, IVU and a combination of ultrasonography combined with CT scout at our institution from May 2013 to December 2014 were reviewed.

Inclusion criteria were 1) ureteric calculus of size less than 5mm, 5 -8 mm or greater than 8mm. 2) Age between 18 to 50 years. Exclusion criteria were 1) ureteric stricture 2) concomitant calculus on the same side 3) bilateral ureteric calculi 4) Urinary tract infection 5) benign prostatic hypertrophy 6) Glucose intolerance or Diabetes mellitus 7) BP less than 100 mm systolic 8) postural hypotension.

All patients were assessed by a structured Performa for epidemiological and clinical details. Investigations to be performed were explained to each patient and written consent was taken. Routine urine examination and renal function tests were done in each case. Serum creatinine < 1.8 mg/dl were included in the study for the use of intravenous contrast.

Procedure

This is a case controlled study conducted in the period from May 2013 to December 2014 at a tertiary hospital. After giving informed consent, 100 adult patients with acute renal colic suspected of having urolithiasis underwent NCCT, IVU & combination of CT scout with Ultrasound (Figure 1-4) within a span of 24 hours. NCCT was performed on a 64-MDCT scanner (Somatom sensation 64, Siemens Healthcare, Germany). The 5-mm-thick slices (at 120-140 kV, l20-180 mAs, with an increment of 6 mm, pitch 1.21) were obtained in a single helical acquisition starting from the mid portion of the 12th thoracic vertebral body to the pubic bone. The total scan time was 40-50 sec during one or two breath-holds. Reconstructed slices at 3-mm intervals were secondarily obtained with a field of view of 25 cm focused on the urinary structures. This procedure yielded 103 reconstructed images, which were then transferred to a workstation (Advantage Windows; General Electric Medical Systems, Milwauki, WI) for processing. Low dose CT Protocol (BMI <30) include automated tube current modulation at KVp 80-120 and mAS 30-109 with radiation dosage of 0.97-1.9 mSv. All CT Scout View were produced using the manufacturer’s default setting at 120 KVp and 1mAs with radiation dosage of 0.83 mSv.

A) B)

Figure 1 USG shows 8mm right mid ureteric calculus [1(b)] resulting in moderate proximal ipsilateral hydroureteronephrosis [1(a)].

Figure 2 CT scout image shows well defined radio-opacity overlying at right sacral ala.

Figure 3 25 minutes delayed prone IVU image shows right mid ureteric calculus with proximal hold up.

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For NCCT, CT scout and Ultrasound, patients were placed in supine position with full urinary bladder. Ultrasonography was done using 3.75 MHz surface probe in Voluson E8 (GE Healthcare, USA). IVU was done using non-ionic iodinated contrast material with radiation exposure in range of 1.3-3.5 mSv. Standard radiation dose of different imaging modalities [5-8] in acute renal colic (non-pregnant adult) were summarised in Table 1.

The unenhanced CT findings were initially interpreted on only the axial images.

In concordance with the radiologic criteria described by Smith et al [3] NCCT criteria for lithiasis were defined by the presence of a high-density structure within the ureter lumen. Obstruction of the urinary tract was considered whenever the ureter was unilaterally dilated above a certain level, below which its caliber was normal. Calculi on US are characteristically demonstrated as highly echogenic foci with distinct acoustic shadowing. Diagnostic criteria include direct visualization of the stone, hydroureter more than 6mm in diameter and hydronephrosis [9]. Each case was evaluated for the presence or absence of secondary signs, comparatively with the contralateral side, whenever a ureteral stone was present with or without obstruction.

Image interpretation

Two experienced radiologists, unaware of the findings, independently reviewed all images to determine the presence or absence of ureteral calculi. Any differences in image interpretation were resolved by consensus.

The effects of Body Mass Index (BMI), Size of calculi, Hydronephrosis, Imaging appearance of calculi, were analyzed statistically to predict the probability of presence or absence of ureteric calculi.

Statistical analysis

Sensitivity, specificity and positive predictive value, negative predictive value and accuracy for detecting ureteral calculi, were determined for NCCT, IVU and combination of CT scout

with US. The variables of Body Mass Index (BMI), Size of calculi, Hydronephrosis, Imaging appearance of calculi, were analyzed for an association with a true-positive diagnostic finding by Fischer’ s exact test. A multivariate logistic regression model was formulated using backward elimination to select variables useful for predicting the presence of ureteric calculi (p < 0.05). The model with the smallest Akaike information criterion value (which is based on likelihood but adds a penalty for a large number of variables) was selected as the final model [10,11]. During the model fitting, the variables were grouped so that small numbers of patients in individual categories would not have resulted in a large variance of coefficients in the logistic regression model. Results were considered statistically significant at p < 0.05. The Hosmer-Lemeshow test was used to evaluate model calibration.

RESULTSOf 100 patients with acute renal colic, 82 had pathologically

proven ureterolithiasis. Clinical follow-up was available in all the stone patients (82) and non-stone patients (18). In 80 of the 82 patients diagnosed with ureteral calculi, the NCCT made the diagnosis. IVU made the diagnosis in 70 of the 82 patients and combination of CT scout with US KUB diagnosed 74 of the 82 patients. Of the 18 patients without ureterolithiasis, the NCCT was negative in all cases. IVU was negative in 16 of the 18 cases. Combination of CT scout & US KUB was negative in 12 of the 18 patients.

Per-patient sensitivity, specificity, positive predictive value, negative predictive value and accuracy for detecting ureteral calculi with NCCT (100% [80/80], 90% [18/20], 97.5% [80/82], 100% [18/18] and 98% [98/100] respectively) were significantly greater than those for IVU (97.2% [70/72], 57.1% [16/28], 85.3% [70/82], 88.8% [16/18] and 86% [86/100]) &

Figure 4 Unenhanced coronal CT image shows 8mm right mid ureteric calculus resulting in moderate proximal ipsilateral hydroureteronephrosis.

Radiologic Method Technique

Radiation exposure (mSv)

Priority order

Low-dose NCCT (BMI<30)

Automated tube current modulationKVp 80-120 and mAS 30- 109

0.97-1.9 1

Regular-dose NCCT (BMI >30)

KVp 120-140 and mAS 120–180.scans were obtained from the upper borderof T12 vertebral body to the lower border ofsymphysis pubis using 5–7 mm collimation

4.5-5 1

IVU Nonionic iodinated contrast material 1.3-3.5 3

CT scout+ US *

KVp 120 and mAS 1.Ultrasonography was done using 3.75 MHz surface probe

0.83-3.8 2

Table 1: Standard Radiation exposure of different imaging modalities [5-8] in acute renal colic (non-pregnant adult) – suspicion of urolithiasis.

NCCT = Non-Contrast Enhanced Computed Tomography*Standardised CT scout dose not specified. In our study the manufacturer default setting for scout view was 1mAs and 120KVP and radiation dose of 0.83 mSv. All latest CT Scanners have reduced the mAs in scout view in attempt to reduce the radiation dose to the patients.

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combination of CT scout with Ultrasound examinations (92.5% [74/80], 60% [12/20], 90.2% [74/82], 66.6% [12/18] and 86% [ 86/100] ) ( p= 0.000) (Table 2).

Table 3 shows detection probability by NCCT, IVU & CT+US when assessed in presence of BMI, Calculi size, Hydronephrosis and Imaging appearance of calculi. Table 4 represents multivariate logistic regression analysis with footnotes explaining the output. Logistic regression analysis is used here because the

outcome is dichotomous. (Calculi present/ absent) and more than one independent variables are present (Body Mass Index (BMI), Size of calculi, Hydronephrosis, Imaging appearance of calculi). These independent variables cannot be linearised and hence computed in tabulated form. Diagnostic performance of three modalities (NCCT, IVU & combination of CT scout with Ultrasound) in presence of independent variables are scored for calculi detection which favours NCCT above the others but shows marginal difference between IVU & CT+US combination.

Validity NCCT IVU Combination of CT scout with US

Sensitivity 100% 97.22% 92.5%

Specificity 90% 57.14% 60%

Positive predictive value 97.56% 85.36% 90.243%

Negative predictive value 100% 88.88% 66.66%

Accuracy 98% 86% 86% Odd’s Ratio(C.I. at 95%) N.A. 46.667

(9.493- 229.404) 18.5

(5.453- 62.769)

Table 2: Percentage validity of the diagnosis of urolithiasis from NCCT, IVU and combination of CT scout with US.

Actual calculi

Detected Detected Detected

NCCTPercentage Correct

IVU Percentage Correct CT+ US Percentage

CorrectAbsent Present Absent Present Absent Present

AbsentPresent

23 0 100.0 21 6 77.8 21 6 77.8

0 77 100.0 2 71 97.3 3 70 95.9Overall Percentage 100.0 92.0 91.0

Table 3: Calculi detection probability by NCCT, IVU& CT+US when assessed in presence of BMI, Calculi size, Hydronephrosis and Imaging appearance of calculi.

NCCT

Variable B (Regression) S.E. Wald ratio df Sig.(p value) Exp(B) (Odds ratio) 95.0% C.I

BMI -0.882 4.095 .000 1 1.000 .414N.A.N.AN.AN.A

Size Of calculi 12.162 2.031 .000 1 0.995 1.913

Hydronephrosis 46.962 4.485 .000 1 0.992 2.484

Imaging Appearance 21.259 4.451 .000 1 0.996 1.70

IVU

Variable B (Regression) S.E. Wald ratio df Sig.(p value) Exp(B) (Odds ratio) 95.0% C.I

BMI -0.084 0.770 0.012 1 0.913 0.920 0.203-4.1591.514-14.793N.A.

0.061-6.145

Size Of calculi 1.555 0.581 7.148 1 0.008 4.733

Hydronephrosis -20.988 6.062 0.000 1 0.997 0.000

Imaging Appearance -0.488 1.175 0.173 1 0.678 0.614

CT+ US

Variable B (Regression) S.E. Wald ratio df Sig.(p value) Exp(B) (Odds ratio) 95.0% C.I

BMI -0.292 0.703 0.172 1 0.678 0.747

0.188-2.9650.676-4.2220.854-5.138.0. .018 -0.480

Size Of calculi 0.524 0.467 1.259 1 0.262 1.689

Hydronephrosis 0.739 0.458 2.606 1 0.106 2.094

Imaging Appearance -2.382 0.841 8.030 1 0.005 0.092

Table 4: Multivariate logistic regression model analysis.

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Body mass index (BMI)

Two groups were made in this category: BMI< 30 & BMI> 30. Out of 82 pathologically proven calculi patients, 50 patients were found to have BMI< 30 and 32 patients were having BMI>30. In 18 proven noncalculi patients, 10 patients were found having BMI< 30 and 8 patients were of BMI>30. Sensitivity, specificity and positive predictive values of calculi detection varied with BMI. Low dose NCCT (0.97-1.9 mSv) in suspected patients with BMI <30 shows sensitivity, specificity and positive predictive value for detecting ureteral calculi 100% [49/49], 91% [10/11] & 98% [49/50] respectively which is significantly higher as compared to Regular dose NCCT (4.5-5mSv) in suspected patients with BMI >30 {sensitivity100% (28/28)], specificity 66.6% (8/12) and positive predictive value 87.5% (28/32)}(p =0.000). However, Low dose NCCT in suspected patients with BMI <30 remains better than CT scout combined with US {sensitivity 98% [47/48], specificity 75% [9/12] & PPV 94% [47/50]} and IVU { sensitivity 93.75% [45/48], specificity 58.33% [7/12] & PPV 90% [45/50]} (P=0.000). Similarly, in suspected patients with BMI>30, Regular dose NCCT shows significantly better results than CT scout combined with US { sensitivity 92.8% [26/28], specificity 50% [6/12] & PPV 81.25% [26/32]} and IVU {sensitivity 88.88% [24/27], specificity 38.46% [5/13] & PPV 85.7% [24/32]} (P<0.005).

Size of calculi

Out of 82 ureteric calculi patients, 20 calculi were less than 5mm in size, 50 calculi were between 5-8 mm & 12 calculi were > 8 mm in dimension. In these three categories, PPV was calculated among NCCT, IVU & combination of CT scout with US. The trends are depicted as follow:

< 5mm NCCT > combination of CT scout with US > IVU

(20 Calculi) (90% [18/20]) (80% [16/20]) (70% [14/20])

5-8mm NCCT > combination of CT scout with US > IVU

(50 Calculi) (98% [49/50]) (94% [47/50]) (90% [45/50])

>8mm NCCT > combination of CT scout with US > IVU

(12 Calculi) (100% [12/12]) (91.6% [11/12]) (83.33% [10/12])

Hydronephrosis

All the 82 calculi patients were found to have hydronephrosis. These are classified into three groups- 1. Mild (40 calculi patients) 2. Moderate (27 calculi patients) 3. Damage to renal function (15 calculi patients). In hydronephrosis, interesting outcome in terms of PPV was noted among the three modalities, as follow:

Mild NCCT = IVU > combination of CT scout with US

(40 calculi patients) 95% [38/40] 95% [38/40] 90% [36/40]

Moderate IVU > NCCT > combination of CT scout with US

(27 calculi patients) 92.6% [25/27] 88.9% [24/27] 81.4% [22/27]

Damage to renal function NCCT > combination of CT scout with US

(15 calculi patients) 93.3% [14/15] 80% [12/15]

{IVU not performed due to renal insufficiency}

Imaging appearance of calculi

Imaging appearance of calculi in terms of fluorescence/opacity found that out of 82 ureteric calculi, 75 were radiopaque & 7 were non- radiopaque. Hence, PPV of NCCT, IVU & combination of CT scout with Ultrasound was determined in two groups – Radiopaque & Non- radiopaque calculi. The readings can be summarized as follow:

Radiopaque NCCT > combination of CT scout with US > IVU

(75 calculi) 100% [75/75] 96% [72/75] 93.3% [70/75]

Non-Radiopaque NCCT > combination of CT scout with US > IVU

(7 calculi) 100% [7/7] 85.7% [6/7] 57.14% [4/7]

DISCUSSION The EUA-AUA [European Association of Urology (EAU) in

collaboration with the American Urological Association (AUA)] Guidelines on the Management of ureterolithiasis recommend that the performance characteristics of various imaging modalities for a given clinical scenario should be assessed appropriately [12]. Recent studies [3,4] have reported NCCT as the most sensitive and specific diagnostic modality for detecting urolithiasis. Consequently, NCCT is frequently used in the initial diagnosis of urolithiasis and in the follow-up of known ureteral calculi before and after treatment. Some studies have shown that low-dose CT in patients with Body Mass Index less than 30 is recommended to limit the potential long term effects of ionising radiation [13-16]. In this series, we tried to correlate BMI>30 with regular dose NCCT (because low dose NCCT gave inferior image contrast in patients with BMI>30 leading to more false positives), IVU and combination of CT scout with US. However, it is interesting to note that combination of CT scout with US in both the groups (BMI <30 & BMI>30) can be a promising modality in future due to low radiation exposure & minimal cost than NCCT. The results suggests NCCT as gold standard but combination of CT scout with US can be used in follow up as well as initial diagnosis in cases with BMI<30. The result section readings of calculi size estimation gave us the impression that increase in size of calculi increase the PPV of each respective modality used in the study. Comparative evaluation in terms of hydronephrosis led to the conclusion that IVU is superior to both NCCT & combination of CT scout with US but it is contraindicated in renal insufficiency cases. PPV estimation trends of size estimation and imaging appearance of calculi also suggest undoubtfully that if NCCT is

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the reference standard in size estimation of calculi, combination of CT scout with US can be used alternatively due to its significant moderate PPV in both the groups.

Ultrasound is dependent on operator’s skill and calculus location [17-19]. However, the focus of this case controlled study is to develop an imaging protocol that guides the clinicians and urologists in detecting location and size of ureteral calculi with least potential harm and has the least resource utilization in terms of cost. Our study provides an objective evidence to assess the clinical efficacy of three modalities NCCT, IVU & combination of CT scout with Ultrasound. This is done by predicting the effects of Body Mass Index (BMI), Size of calculi, Hydronephrosis, Imaging appearance of calculi on the probability of the presence of ureteral calculi in patients with positive radiodiagnostic examination. This is assessed and analysed logistically in the form of a multivariate regression model. Studies have shown sensitivity of the CT scout view in detecting renal calculi to be between 40 to 49%. Chu et al [2] showed sensitivity of 49% is similar to 47% of Assi et al [20] and 40% of Ege et al [21]. Recent studies of Johnston et al [1] showed that the sensitivity of scout radiographs was 47% and Yap et al have shown that the sensitivity of CT scout view is between 42% and 52% [22]. Statistically significant difference from the previous studies arose due to difference in the default manufacturer setting for scout view. Also, bowel gases hindered visualization of calculus. Thus implying manufacturer setting for scout view is an important variable that has to be considered when interpreting a CT scout radiograph.

In our study the manufacturer default setting for scout view was 1mAs and 120KVP and radiation dose of 0.83 mSv. All latest CT Scanners have reduced the mAs in scout view in attempt to reduce the radiation dose to the patients. But this also decreases the image quality hence its ability to detect ureteric calculus. Hence there is decreased sensitivity in detecting stones along with decreased radiation. But a combination of CT Scout with US overcome this limitation and improves sensitivity. It also increases specificity and PPV. Most of the studies [23-27] have reported sensitivities of 58-100% and specificity of 38-100%.

In our study, out of 82 calculi, 74 ureteric calculi were detected with this combination, leading to a sensitivity of 92.5% and specificity of 60%.

Compared with IV urography, Non-contrast unenhanced spiral CT and combination of CT scout with US can be performed rapidly, without patient preparation, and there is no risk of a contrast reaction. However, IVU is not used routinely these days due to persistent nephrogram on delayed IVU. Other relative contraindications include renal insufficiency, dehydration, past reaction to iodinated contrast agents, and pregnancy. Another limitation is its inability to identify alternative diagnoses. But our research shows its superb performance in assessing the degree of hydronephrosis. In our study, IVU located 38 out of 40 cases of mild hydronephrosis and 25 out of 27 cases of moderate hydronephrosis which is almost equivalent to NCCT. Moreover, minimal radiation exposure, no intravenous contrast, usage in cases of renal damage and significantly reduced cost indicates combination of CT scout with ultrasound as novel diagnostic approach. Thus, it can be said undoubtfully that if NCCT is the gold standard in diagnosing ureterolithiasis, combination of CT

scout with US can be used alternatively due to its significant moderate sensitivity, positive predictive value and accuracy.

CONCLUSIONA decisive approach should be developed to select the most

effective imaging study for a given clinical scenario. Our study shows that though NCCT remains the gold standard in initial diagnosis of urolithiasis, CT scout combined with ultrasonography offers a novel combination of sensitivity/specificity with minimal radiation exposure as it can assess the calculus location as well as other associated secondary signs. This combination is cheaper, gives less radiation and requires no intravenous contrast. It should be used in follow up imaging. The studies regarding the follow-up of ureteric calculi with this combination are low and there is limited information in the retrieved articles. However, further studies are recommended to conclude that a combination of CT scout and US can be used in follow-up imaging, instead of NCCT.

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Cite this article

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