The results of the present study demonstrated that there is a high agreement between MRVCUG and VCUG in diagnosis of VUR and determining its severity in high grades, especially grade III-V reflux, despite some limitations of MRVCUG in detecting grade I-II reflux.
Imaging is the base of diagnosis and management (VUR). Recent technological advances have expanded the diagnostic capabilities of MRI to include the pediatric genitourinary tract. These advances include faster image acquisition, enhanced resolution, reduced motion artifact, improved signal-to-noise ratio, and the generation of three-dimensional reconstruction. To the best of our knowledge, only three studies have evaluated the agreement of VCUG and MRVCUG imaging methods.[13
Initial study on MRVCUG has shown sensitivity about 90% for diagnosis of VUR.[13
] This study suffered from some withdraws including lack of detailed imaging method. Following studies on 23 and 44 kidney-ureter units, however, came over to these flaws and have provided complementary data considering application of MRI in rolling out of people without VUR.
Study by Lee et al
] on 23 kidney-ureter units using VCUG as the gold standard, showed different sensitivity and specificity for MRVCUG, while the resulted positive and negative predictive values were in the same range as shown by our study. Takazakura et al
] in a comparison of MRVCUG and traditional VCUG as a standard showed that MRVCUG had a similar sensitivity, but higher specificity, positive and negative predictive values. Like our findings, the presence of high-grade VUR (grade III-V) was correctly diagnosed with MRVCUG in all cases in their study. Another newly published study,[16
] comparing interactive MRVCUG accuracy, have reported higher sensitivity, specificity and NPV with lower PPV. These differences in accuracy may rise from different methods of MRI used by studies.
In base of the preset study, VUR was not diagnosed in three kidney-ureter units during MRVCUG, while diagnosed in VCUG; as same as of two major previous studies reported five[14
] and two[15
] false negative kidney-ureter units. All of undiagnosed kidney-ureter units had mild/grade I VUR. Some possible explanations for this false negative reports and discrepancy between VCUG and MRVC would be the paraureteral bladder diverticulum which is known to cause intermittent VUR,[17
] incomplete voiding due to sedation in infants and young children during MRVCUG, prolonged scan time of MRVCUG, proficiency in MRI technique and temporal relief of VUR. Importantly, all three false negative cases were among grade I VUR in VCUG. Collectively, the higher sensitivity of MRVCUG in comparison to its specificity and also invasive nature of VCUG, make the noninvasive MRVUG a considerable tool for screening VUR in children and adolescent with recurrent UTI.
Out of 44 kidney-ureter units with VUR in MRVCUG, six diagnosed as normal in VCUG evaluation and considered as false positive in our study. All of the false positive cases reported to have mild VUR in MRVCUG. Lee et al
] Takazakura et al
] and Arthurs et al
] reported respectively two, one and three false positive kidney-ureter units on MRVCUG, all of which were cases of mild reﬂux. This misdiagnosis was maybe due to newly developed or early period of development of low grade VUR.
All of false positive and negative cases are among patients with mild/grade I and II VUR. In the clinical setting, patients with low grade reflux do not have an increased risk for recurrence of UTI/renal damage and can usually be managed conservatively;[6
] therefore, such patients usually do not need further imaging for VUR. Despite this fact, the major role of imaging studies in patients with VUR is to identify the presence of high grade reflux for appropriate management to prevent complications. In this regard, MRVCUG has a significant clinical value as follow-up tools for patients who underwent surgical intervention, as well as for patients with high-grade reflux who are under conservative medical management.
Although because of dynamiting characteristic of VUR, VCUG probably has an advantage over MRVCUG in the revealing of VUR, it has limitations in the assessment of morphologic abnormalities of the kidneys, including renal damage or reflux nephropathy. Thus, MRVC has an advantage over VCUG in this regard.
Another important limitation of VCUG is radiation exposure.[18
] It is estimated that as much as 25% of the radiation with potential to produce genetic alterations received by the pediatric population, is related to imaging of the urinary system, especially with VCUG. Also another imaging method is radionuclide cystography which imparts a gonadal radiation dose less than that with conventional VCUG, but it does not provide the same anatomic detail.[19
] Therefore, because of the unpleasant nature of the radiographic imaging and the concerns over radiation exposure, as early as the 1960s, attempts were being made to find alternative VUR diagnostic methods in an effort to eliminate the radiation exposure intrinsic in ﬂuoroscopic and scintigraphic reﬂux examinations.[20
] Today, MRI is known as a powerful diagnostic tool giving precise anatomic detail without the use of ionizing radiation.
Although the present study among finger count studied evaluation diagnostic value of MRI in rule outing VUR, however, it suffers from some limitations like small sample size and short duration which means larger studies with longer-term follow-ups are still needed. Furthermore, carrying out of MRVCUG is limited by some factors including the need for IV sedation/anesthesia in children[22
] and cardiopulmonary monitoring, the difficulty for children to void while supine, increased ureteral flow due to hydration and the use of diuretic may worsen the detection of VUR (increased antegrade ureteral flow), possible heavy work load on the MR equipment due to the relatively long examination time required, and the cost and limited availability of MRI scanners. In this age of cost containment, there are increased costs associated with MRI and availability remains limited. Although MRI is currently more costly, the comprehensive information obtained may justify its use, especially as it does not use ionizing radiation.