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ORIGINAL ARTICLE
Year : 2016  |  Volume : 21  |  Issue : 4  |  Page : 169-174
 

Comparison of intravenous urography and magnetic resonance urography in preoperative evaluation of pelvi-ureteric junction obstruction in children


1 Department of Radiodiagnosis and Imaging, Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Pediatric Surgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Date of Web Publication19-Jul-2016

Correspondence Address:
Kushaljit Singh Sodhi
Department of Radiodiagnosis and Imaging, Postgraduate Institute of Medical Education and Research, Sector-12, Chandigarh - 160 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-9261.186546

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   Abstract 

Aims: To compare intravenous urography (IVU) and magnetic resonance urography (MRU) in the preoperative evaluation of pelvi-ureteric junction obstruction (PUJO) in children. Materials and Methods: A total of 35 children up to 10 years of age in whom unilateral or bilateral PUJO were suspected on ultrasonography were enrolled in this prospective study. All children underwent IVU and MRU, and the findings were compared. Results: Of the 70 kidneys evaluated, 14 (20%) were not visualized on IVU because of nonexcretion of contrast, whereas all the 70 (100%) kidneys were visualized on MRU. On IVU, nephrogram was not visualized in 66 (94.2%) of the 70 kidneys, whereas MRU showed prompt and homogeneous nephrogram in 68 (97.1%) of the 70 kidneys. No evidence of PUJO was seen in 31 (44.2%) kidneys on both IVU and MRU. IVU showed PUJO in 26 (37.1%) kidneys, whereas MRU showed it in 38 (54.2%) kidneys. MRU detected two duplex systems that were missed on IVU. A focal renal lesion and two incidental extra renal abnormalities were detected on MRU, which were not visualized on IVU. Conclusion: MRU is better than IVU, especially in case of poorly functioning kidneys which are not visualized on IVU. MRU also provides anatomic details of the ureter and vessels with better evaluation of renal parenchyma. It also has an additional advantage of detecting incidental extra renal abnormalities, if present.


Keywords: Intravenous urography, magnetic resonance urography, pelvi-ureteric junction obstruction


How to cite this article:
Sharma A, Sodhi KS, Saxena AK, Bhatia A, Menon P, Rao KL, Khandelwal N. Comparison of intravenous urography and magnetic resonance urography in preoperative evaluation of pelvi-ureteric junction obstruction in children. J Indian Assoc Pediatr Surg 2016;21:169-74

How to cite this URL:
Sharma A, Sodhi KS, Saxena AK, Bhatia A, Menon P, Rao KL, Khandelwal N. Comparison of intravenous urography and magnetic resonance urography in preoperative evaluation of pelvi-ureteric junction obstruction in children. J Indian Assoc Pediatr Surg [serial online] 2016 [cited 2019 Sep 15];21:169-74. Available from: http://www.jiaps.com/text.asp?2016/21/4/169/186546



   Introduction Top


Pelviureteric junction obstruction (PUJO) is defined as an obstruction to the flow of urine from renal pelvis into the ureter. [1] It is the most common cause of hydronephrosis in children, and it becomes difficult for radiologists and urologists to decide which children are going to benefit from the surgery. [2],[3],[4],[5]

PUJO can be idiopathic or as a result of a neuromuscular abnormality at the (PUJ). Aberrant lower pole vessels, kinks, adhesions, and abnormal angulations may also sometimes cause PUJO. The renal damage due to obstruction depends mainly on the time of onset, location, and degree of obstruction. Renal damage is due to a complex interplay of many vasoactive mediators and cytokines leading to alteration of glomerular and tubular function and not simply a result of mechanical obstruction to the flow of urine. [6],[7]

Hydronephrosis is self-limited in many cases with no long-term sequelae. [8] However, renal function deteriorates in some children. This variable outcome makes it difficult to take the decision for surgery as many children will improve only on conservative management. [9],[10] Only 25-50% of children with detected hydronephrosis in antenatal period require surgery. Primary conservative management is currently advocated by many experts for infants with hydronephrosis with close follow-up and surgery only if there is evidence of decreased renal function or progressive hydronephrosis. [11],[12] This requires follow-up imaging.

Ultrasonography (USG), intravenous urography (IVU), and scintigraphy are the main investigations for the evaluation of obstructed uropathy. USG is the initial investigation in the evaluation of an obstructed system. IVU has since long served as an important investigation for urinary tract abnormalities, but it has many drawbacks such as impaired image quality as a result of bowel gas, long examination time along with risks involved due to ionizing radiation, and iodinated contrast media. IVU is especially not justified in young patients because of high doses of radiation involved, and there is risk of contrast nephrotoxicity in dehydrated subjects. It may also lead to hypersensitivity reactions. Magnetic resonance imaging does not involve any ionizing radiation, hence is safe to use in children. [13],[14] Magnetic resonance urography (MRU) not only provides anatomical details but also the functional status of kidneys. MRU also helps in deciding the prognosis by assessing the renal parenchyma and thus identifying extent of renal damage preoperatively.

No published data are available from the Indian subcontinent comparing the IVU and MRU. This study was conducted to evaluate the role of MRU as radiation-free modality in the preoperative evaluation of PUJO in pediatric population.


   Materials and methods Top


This study was conducted in a tertiary-care teaching hospital of Northern India after obtaining approval from the Ethics Committee of the institute. The study included 35 children up to 10 years of age in whom unilateral or bilateral PUJO was suspected on USG. Children with deranged renal function tests were excluded.

IVU was performed on a Radiotex system (DAR-3K, model 1A-12 LD11; Shimadzu, Tokyo, Japan).

Procedure for intravenous urography

  1. Preliminary imaging: Kidney-ureter-bladder radiograph was conducted to ascertain technique and level
  2. Antecubital vein was cannulated, and an injection of 2-3 ml/kg of nonionic iodinated contrast medium, iohexol (nonionic monomer, Omnipaque 300; Nycomed, Cork, Ireland), was administered over 1 min
  3. Serial films were obtained at 7, 15, and 30 min intervals. Films were again obtained after 1, 2, and 4 h as per the merits of the case. The objective was to monitor opacification of the pelvicalyceal system (PCS), ureter, and bladder
  4. Lasix (0.1 mg/kg body weight) was administered intravenously in all cases of outflow tract dilatation to assess the degree of obstruction to drainage subjectively. It was administered when dilated PCS was well opacified. Images were acquired 10 and 20 min after Lasix administration
  5. A full-bladder image was obtained. Optional oblique images, repeat tomograms, upright images, prone, or delayed images were obtained wherever required.


MRU was performed on a 3-T MRI scanner (Verio; Siemens and Erlangen, Germany) or a 1.5-T MRI scanner (Avanto, Siemens and Erlangen, Germany) installed at the Department of Radio Diagnosis and Imaging.

Procedure for magnetic resonance urography

MRU was performed using a body coil, with gadopentetate dimeglumine (gadolinium-diethylenetriamine pentaacetic acid) at 0.1 mmol/kg body weight.

Lasix was administered IV (1 mg/kg body weight) after 15 min of contrast injection.

The sequence protocol was:

a. Scout

1. Localizer: T2 HASTE axial, sagittal, and coronal

b. Precontrast sequences

  1. T2 HASTE fat saturation: Axial
  2. T2 HASTE fat saturation: Coronal
  3. T1 VIBE fat saturation: Coronal


c. Postcontrast sequences

  1. T1 VIBE fat saturation: Coronal; 5 min after contrast
  2. T1 VIBE fat saturation: Coronal; 15 min after contrast


d. Post-Lasix sequences

1. T1 VIBE fat saturation: Coronal; 10 min after Lasix.

The time interval between IVU, MRU, and other radiological investigations was fewer than 2 weeks.

The grading of hydronephrosis in our study was performed by MRU as MRU is similar to sonography in its ability to categorize the degree of hydronephrosis. [15]


   Results Top


There were 30 male patients (85.7%) and 5 female patients (14.3%). The duplex system was not detected in any of the 35 children on IVU, whereas MRU was able to detect duplex systems in 2 children.

[Table 1] summarizes the findings on IVU and MRU in our study.
Table 1: The findings on intravenous urography and magnetic resonance urography in our study

Click here to view


Of the six right kidneys that were not visualized on IVU, MRU showed four to be enlarged, one normal-sized, and one shrunken. Seven kidneys appeared to be enlarged on IVU, of which four were found to be of normal size and three enlarged on MRU. Twenty-two kidneys were found to be of normal size on both MRU and IVU.

Of the eight left kidneys that were not visualized on IVU, MRU showed five to be enlarged, two normal-sized, and one shrunken. Fourteen kidneys appeared to be enlarged on IVU, of which seven were found to be of normal size and seven enlarged on MRU. Thirteen kidneys were of normal size on IVU, of which 2 appeared enlarged and 11 normal-sized on MRU.

Of the seven left renal PCS in which no contrast excretion was seen on IVU, MRU showed prompt contrast excretion in two, delayed contrast excretion in three, and no contrast excretion in two.

On the right side, 20 of 35 kidneys showed no PCS dilatation on both IVU and MRU. On IVU, 20 kidneys showed no PCS dilatation, 9 showed dilated PCS, whereas 6 showed no contrast excretion in PCS. Of these six nonvisualized kidneys, five showed Grade 4 hydronephrosis and one showed no PCS dilatation on MRU. However, 21 kidneys showed no PCS dilatation and the remaining 14 showed dilated PCS on MRU.

On the left side, 8 of 35 kidneys showed no PCS dilatation on both IVU and MRU. On IVU, 10 kidneys showed no PCS dilatation, 18 showed dilated PCS, whereas 7 showed no contrast excretion in PCS. Of these seven nonvisualized kidneys, six showed Grade 4 hydronephrosis and one showed Grade 2 hydronephrosis on MRU. However, 8 kidneys showed no PCS dilatation and the remaining 27 showed dilated PCS on MRU.

Of the 35 right kidneys, 21 (60%) showed no evidence of PUJO on both IVU and MRU. Of the 35 left kidneys, 10 (28.5%) showed no evidence of PUJO on both IVU and MRU.

Urinary bladder was normally visualized in all 35 children on both IVU and MRU. On IVU, no focal lesion was seen in either kidney in all 35 children, whereas on MRU, a tiny simple cortical cyst was seen in the right kidney of one of the children. On MRU, incidental extra renal abnormalities were detected in 2 of the 35 children. One of them had bilateral undescended testis, and the other had a cystic lesion in pelvis. These findings were not seen on IVU.

[Figure 1],[Figure 2],[Figure 3] and [Figure 4] show IVU and MRU findings in four different cases.
Figure 1: (a-c) Left kidney not visualized on intravenous urography till 2 h of study. (d) Magnetic resonance urography image (T2-weighted image) showing pelviureteric junction obstruction in left kidney. (e) Magnetic resonance urography image (postcontrast T1-weighted image) shows nonexcretion of contrast on the left side

Click here to view
Figure 2: (a and b) Left kidney not visualized on intravenous urography till 4 h of study. (c) Magnetic resonance urography image (T2-weighted image) shows small, hydronephrotic left kidney. (d) Magnetic resonance urography image (postcontrast T1-weighted image) shows nonexcretion of contrast in the small hydronephrotic kidney on the left side

Click here to view
Figure 3: (a and b) Left kidney not visualized on intravenous urography till 2 h of study. (c) Magnetic resonance urography image (T2-weighted image) showing pelviureteric junction obstruction in the left kidney. (d) Magnetic resonance urography image (postcontrast T1-weighted image) shows nonexcretion of contrast on the left side

Click here to view
Figure 4: (a) Intravenous urography showing bilateral pelviureteric junction obstruction. (b and c) T1-weighted postcontrast images show pelviureteric junction obstruction on the right side and hydroureteronephrosis on the left side

Click here to view



   Discussion Top


USG, IVU, and scintigraphy have long been used as the initial investigations for the evaluation of obstructed kidneys, USG being the initial screening test. IVU has long been considered as an important imaging modality for the evaluation of urinary tract disease. However, its dependency on ionizing radiation makes it inappropriate in children. An obstructive curve on renal scintigraphy and the clinical assessment of the patient serve as important parameters in making the decision for surgery. Scintigraphy also involves ionizing radiation such as IVU, and it evaluates renal function but with poor resolution of anatomy.

MRU is a step ahead in evaluation of the urinary tract abnormalities as it not only provides good anatomic detail but also helps in functional assessment of kidneys with no risk of ionizing radiation. [11] The risk of contrast nephrotoxicity and hypersensitivity reactions is also much less than that involved in IVU. Hence, it offers a comprehensive evaluation in a single test.

Different protocols regarding the timing of furosemide injection have been used in nuclear medicine studies and have been transposed to MRU. [16] We chose the F+15 technique (furosemide injection 15 min after the contrast injection). This technique offers anatomic assessment at baseline with or without furosemide-induced distension, and it also obviates the need for bladder catheterization as there is no early over distension of bladder.

Borthne et al. [17] compared MRU with renal scintigraphy in 39 children to determine its potential and effectiveness. Nine percent of examinations were nondiagnostic or interrupted due to movement. MRU provided additional information in 66%.

The major drawback of IVU was nonvisualization of severely obstructed, poorly functioning kidneys (either left or right) because of poor contrast excretion. MRU helped in picking up important renal findings which altered the management protocol, especially in the cases where kidneys were not visualized on IVU. Duplex system was seen in two patients in our study, which was not picked up on IVU. Similarly, some of the kidneys were not visualized on IVU. On MRU, all the kidneys were seen, and the size was normal, enlarged, or shrunken. The major advantage of MRU was in the visualization of nonfunctioning kidneys where the static MRU sequences were able to confirm the diagnosis of PUJO. This may obviate the need for the contrast administration in cases with compromised renal function, and there is increased risk of renal toxicity. Nephrogram was not visualized on IVU in most of the kidneys mostly due to obscuration by bowel shadows. Almost all these kidneys showed prompt and homogeneous nephrogram on MRU. Similarly, we could better visualize the ureter on MRU, on which the entire course of the ureter could be traced.

On comparison of IVU and MRU, we found that the site of stenosis in the urinary tract was better localized on MRU. MRU also offered information regarding the morphology of renal parenchyma. On MRU, architectural disorganization with loss of the corticomedullary differentiation, small subcortical cysts, and low cortical T2 signal intensity suggest underlying uropathy changes and permanent damage. However, a decompensated kidney typically shows increased signal intensity on T2-weighted image, which reflects edema as well as a delayed dense nephrogram. These patterns have different prognostic implications with little improvement in renal function is expected following pyeloplasty in kidneys with changes of uropathy, but significant improvement is seen in decompensated systems. [15] However, this was not addressed in our study.

MRU also has an additional advantage of detecting incidental extrarenal abnormalities, if present. [16] In our study, a tiny simple cortical cyst was seen in the right kidney of one of the children. Extra renal abnormalities were detected in 2 of the 35 children. One of them had bilateral undescended testis, and the other had a cystic lesion in pelvis. None of these findings could be picked up on IVU. Furthermore, MRU detected duplex system in two patients which were missed on IVU.

MRU examinations took approximately 30 min on an average whereas, in IVU, several radiographs had to be performed with total period extending up to 4 h in cases of urinary tract obstruction.

In our study, there were problems mainly related to patient movement. However, none of the examinations was abandoned because of inadequate sedation and immobilization. Image quality was also affected by respiratory motion artifacts.

However, there may be concern regarding the costs involved in MRU as cheaper modalities such as USG, IVU, and scintigraphy are readily available. Furthermore, the availability of pediatric MRU is still limited. However, as MRU offers a comprehensive evaluation of renal function and urinary drainage, it has the potential to replace both IVU and scintigraphy. Thus, a single imaging modality would provide all the information, and it would no longer increase costs when compared to the combination of conventional methods.

MRU requires sedation and sometimes, even anesthesia. However, sedation may also be needed in some infants for scintigraphy, and the duration of scintigraphy is also generally longer than that of MRU examinations. Therefore, the need for sedation during MRU does not increase the invasiveness of examination while reducing the overall radiation burden. In addition, some of the pathologies may only be seen with MRU; and therefore, its advantages outnumber its disadvantages.

Furthermore, programs are available to calculate relative renal function in MRU. [11],[15],[16] However, this was not addressed in our study. These programs further enhance the value of MRU over scintigraphy as currently scintigraphy has the advantage of quantitative data. This is a limitation of our study, although anatomical information provided by MRU is better than nuclear scintigraphy. Furthermore, we did not evaluate the renal parenchymal signal intensity patterns. In future, MRU may become the investigation of choice that offers simultaneous and reliable assessment of anatomic and functional details in obstructed urinary tract. However, long-term studies are needed to assess the reliability of MRU as in differentiating actual obstruction from secondary phenomena such as dilatation or delayed drainage. We also suggest further studies comparing MRU with IVU combined with scintigraphy.


   Conclusion Top


To conclude, MRU has the potential to replace IVU and emerge as the imaging modality of choice in evaluating poorly functioning obstructed systems which are not visualized on IVU. MRU is a cross-sectional imaging modality with high image quality which provides good insight into the anatomy and basic pathophysiological mechanisms involved in causing renal damage in obstructed systems. It offers additional advantage in evaluating complex pathologies such as ectopic insertion of the ureter and suspected renal buds. However, there is a need to device specific protocols for different indications to optimize imaging efficacy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Neste MG, du Cret RP, Finlay DE, Sane S, Gonzalez R, Boudreau RJ, et al. Postoperative diuresis renography and ultrasound in patients undergoing pyeloplasty. Predictors of surgical outcome. Clin Nucl Med 1993;18:872-6.  Back to cited text no. 1
    
2.
Grignon A, Filiatrault D, Homsy Y, Robitaille P, Filion R, Boutin H, et al. Ureteropelvic junction stenosis: Antenatal ultrasonographic diagnosis, postnatal investigation, and follow-up. Radiology 1986;160:649-51.  Back to cited text no. 2
    
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Figenshau RS, Clayman RV. Endourologic options for management of ureteropelvic junction obstruction in the pediatric patient. Urol Clin North Am 1998;25:199-209.  Back to cited text no. 3
    
4.
Ransley PG, Dhillon HK, Gordon I, Duffy PG, Dillon MJ, Barratt TM. The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J Urol 1990;144 (2 Pt 2):584-7.  Back to cited text no. 4
    
5.
Chevalier RL. Effects of ureteral obstruction on renal growth. Semin Nephrol 1995;15:353-60.  Back to cited text no. 5
    
6.
Wen JG, Frøkiaer J, Jørgensen TM, Djurhuus JC. Obstructive nephropathy: An update of the experimental research. Urol Res 1999;27:29-39.  Back to cited text no. 6
    
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Klahr S. Urinary tract obstruction. Semin Nephrol 2001;21:133-45.  Back to cited text no. 7
    
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González R, Schimke CM. Ureteropelvic junction obstruction in infants and children. Pediatr Clin North Am 2001;48:1505-18.  Back to cited text no. 8
    
9.
Chandrasekharam VV, Srinivas M, Bal CS, Gupta AK, Agarwala S, Mitra DK, et al. Functional outcome after pyeloplasty for unilateral symptomatic hydronephrosis. Pediatr Surg Int 2001;17:524-7.  Back to cited text no. 9
    
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Koff SA, Campbell KD. The nonoperative management of unilateral neonatal hydronephrosis: Natural history of poorly functioning kidneys. J Urol 1994;152 (2 Pt 2):593-5.  Back to cited text no. 10
    
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Grattan-Smith JD, Jones RA. MR urography: Technique and results for the evaluation of urinary obstruction in the pediatric population. Magn Reson Imaging Clin N Am 2008;16:643-60.  Back to cited text no. 11
    
12.
Grattan-Smith JD, Little SB, Jones RA. MR urography evaluation of obstructive uropathy. Pediatr Radiol 2008;38 Suppl 1:S49-69.  Back to cited text no. 12
    
13.
Sodhi KS, Khandelwal N, Saxena AK, Bhatia A, Bansal D, Trehan A, et al. Rapid lung MRI - Paradigm shift in evaluation of febrile neutropenia in children with leukemia: A pilot study. Leuk Lymphoma 2016;57:70-5.  Back to cited text no. 13
    
14.
Sodhi KS, Khandelwal N, Saxena AK, Singh M, Agarwal R, Bhatia A, et al. Rapid lung MRI in children with pulmonary infections: Time to change our diagnostic algorithms. J Magn Reson Imaging. 2015. doi: 10.1002/jmri.25082. [Epub ahead of print].  Back to cited text no. 14
    
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Jones RA, Perez-Brayfield MR, Kirsch AJ, Grattan-Smith JD. Renal transit time with MR urography in children. Radiology 2004;233:41-50.  Back to cited text no. 15
    
16.
Darge K, Anupindi SA, Jaramillo D. MR imaging of the abdomen and pelvis in infants, children, and adolescents. Radiology 2011;261:12-29.  Back to cited text no. 16
    
17.
Borthne A, Nordshus T, Reiseter T, Geitung JT, Gjesdal KI, Babovic A, et al. MR urography: The future gold standard in paediatric urogenital imaging? Pediatr Radiol 1999;29:694-701.  Back to cited text no. 17
    


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