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Saudi Journal of Kidney Diseases and Transplantation
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Table of Contents   
ORIGINAL ARTICLE  
Year : 2011  |  Volume : 22  |  Issue : 2  |  Page : 225-231
Can contrast-enhanced renal MR angiography replace conventional angiography in preoperative evaluation of living renal donors?


1 Department of Radio Diagnosis, Faculty of Medicine, Cairo University, Egypt
2 Department of Urology, King Fahd Military Medical Complex, Dhahran, Kingdom of Saudi Arabia

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Date of Web Publication18-Mar-2011
 

   Abstract 

The aim of the study was to detect if gadolinium-enhanced renal magnetic reso­nance angiography (MRA) can replace conventional angiography in imaging vascular anatomy in potential living renal donors and compare with surgical findings. MR imaging (MRI) and breath-hold three-dimensional gadolinium-enhanced MRA of kidneys were done for 60 conse­cutive patients for whom successful nephrectomy was done. MRA findings were compared with the findings of nephrectomy. MRI and MRA identified 28 out of 60 patients with normal arterial and venous anatomy, and concordance was found at surgery in 27 of these patients. Vascular anomalies were depicted on MRI in 32 patients, with concordance at surgery in 27 patients. Re­garding arterial anomalies, the MRA had a sensitivity of 89.3%, a specificity of 94.0% and an accuracy of 90.8%. For venous anomalies, the sensitivity was 98.5%, specificity was 100% and accuracy was 98.6%. In conclusion, gadolinium-enhanced MRA of the kidneys can replace con­ventional angiography as a safe and accurate modality for the assessment of potential living renal donors.

How to cite this article:
Emam AT, Aloraifi IA, Egail SA. Can contrast-enhanced renal MR angiography replace conventional angiography in preoperative evaluation of living renal donors?. Saudi J Kidney Dis Transpl 2011;22:225-31

How to cite this URL:
Emam AT, Aloraifi IA, Egail SA. Can contrast-enhanced renal MR angiography replace conventional angiography in preoperative evaluation of living renal donors?. Saudi J Kidney Dis Transpl [serial online] 2011 [cited 2014 Sep 2];22:225-31. Available from: http://www.sjkdt.org/text.asp?2011/22/2/225/77593

   Introduction Top


Kidney transplants from living donors have become increasingly common in the past de­cade due to better outcome and shortage of available cadaveric kidneys. Anatomic assess­ment of the donor kidney is performed prior to transplantation to aid in the selection of kid­ney and plan the surgical approach. [1]

Multiple imaging modalities have been used for the preoperative evaluation of renal do­nors, including sonography, computed tomo­graphy (CT), scintigraphy, intravenous urography, conventional angiography and magnetic resonance imaging (MRI). [2]

Magnetic resonance angiography (MRA) has been used as a minimally invasive means of preoperative radiologic evaluation of renal do­nors. Recent studies with gadolinium-enhanced MRA have established it as an accurate ima­ging modality for the visualization and eva­luation of living renal donors for open nephrectomy. [3],[4],[5]

Contrast-enhanced MRA (CE-MRA) and digital subtraction angiography (DSA) are com­parable for detecting arterial renal variants, while CE-MRA is superior for identifying venous variants. The preoperative choice of transplant kidney was not significantly influenced by the different results of CE-MRA and DSA. [6]

We evaluated the effectiveness of gadoliniumenhanced MRA in a group of renal donors un­dergoing donor nephrectomy and compared our prospective interpretation of MR images with the surgical findings.


   Subjects and Methods Top


Our study includes 60 potential kidney do­nors consisting of 34 males and 26 females with age ranging from 18 to 62 years (mean age 39.4 years) in whom successful nephrectomy was performed between January 2004 and August 2008 at King Fahd Military Medical Complex. All patients were evaluated with MRI as a part of the preoperative assessment for potential donation. We compared MR angio­graphic findings with the operative results.

MRI was performed using a 1.5-T unit (Infi­nity Echo Speed GE Medical Systems, Milwau­kee, WI, USA) and a torso phased array coil. Imaging was typically completed in 45 minutes.

Images of the renal parenchyma were ob­tained before contrast agent administration with breath-hold axial and coronal Tl-weighted in­phase and opposed-phase gradient-echo MRI, breath-hold axial and coronal Tl-weighted fat­saturated gradient-echo imaging, and breath­hold axial and coronal half-Fourier acquisition single-shot turbo spin-echo imaging.

Gadolinium-enhanced MRA was performed using a coronal breath-hold three-dimensional fat-saturated spoiled gradient-echo technique.

An injection of gadopentetate dimeglumine (Gd) 0.2 mmol/kg (Magnevist; Schering, Berlin, Germany) was given at a rate of 4 mL/s into an antecubital vein by using an 18-gauge cannula, with an MRI-compatible power injector (Spectris; Medrad, Pittsburgh, PA, USA). The bolus of contrast material was followed by a 20-mL bolus of saline. After bolus injection, the patients underwent imaging without a scan delay. A total of three acquisitions were obtained in each patient, with the first acquisition appro­ximately 20 s after the contrast agent adminis­tration. Delayed imaging of the renal paren­chyma was performed with breath-hold axial and coronal Tl-weighted fat-saturated gradientecho imaging.

Maximum-intensity-projection imaging and multiplanar reconstruction were performed. MRI interpretation was based on film hard­copy images from all the available pulse se­quences described.

Arterial vascular anatomy of each kidney was detected regarding the number and size of re­nal arteries and the presence of early extrahilar branching (defined as branching occurring within the proximal 2.0 cm from the renal artery ostium) [Figure 1], [Figure 2]. Renal venous anatomy was evaluated for the presence of accessory renal veins, retroaortic or circumaortic variants and lumbar vein drainage into the renal veins. The renal parenchyma was evaluated to assess fo­cal lesions.
Figure 1: Single renal artery on both sides in a 22-year-old man. Coronal and axial maximumintensity-projection image obtained from threedimensional spoiled gradient-echo gadoliniumenhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20°) shows single renal arteries.

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Figure 2: Early branching of the left renal artery in a 42-year-old man. Coronal maximumintensity-projection image obtained from threedimensional spoiled gradient-echo gadoliniumenhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20°) shows early branching of left renal artery (arrow).

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The MRI findings were compared with the surgical findings, which were based on re­views of the operative reports and interviews of the surgeons. The cases of all patients with discrepant findings at surgery were reviewed.

We calculated the sensitivity, specificity and accuracy of MRA for the determination of vas­cular anomalies. The results obtained at surgery were used as the gold standard in our analysis. For further analysis, a paired Student's t-test was used.


   Results Top


All MRI examinations were carried out with­out complications. No obvious abnormalities of the renal parenchyma were described on MRI or seen at surgical resection.

The left kidney was chosen as the harvest site in 28 patients with normal arterial and venous anatomy [Figure 1] as the left kidney has a longer vascular pedicle compared to the right one.

[Table 1] shows the concordance and discre­pancy of MRA results and that of surgery. Vascular anomalies (arterial or venous) were described on MRA in 32 patients, with com­plete concordance seen with the surgical fin­dings in 27 patients and discrepancy in 5 [Table 2].
Table 1: Concordance and discordance of the results of MRA and surgery.

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Table 2: Cases of discordance of MRA and surgery.

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Accessory renal artery was the commonest renal vascular anomaly [Figure 3], [Figure 4], [Figure 5] followed by early branching of renal artery [Figure 2] and [Table 3].
Figure 3: Small accessory left renal artery in a 49-year-old man. Coronal maximum-intensityprojection image obtained from three-dimensional spoiled gradient-echo gadolinium-enhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20°) shows normal renal arteries bilaterally with an accessory left renal artery (arrow) arising from the aorta.

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Figure 4: An accessory right renal artery in a 53-year-old man. Coronal maximum-intensity-projection image obtained from three-dimensional spoiled gradient-echo gadolinium-enhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20°) shows dual right renal artery arising from the aorta (arrow).

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Figure 5: Bilateral renal artery anomalies in a 35- year-old man. Maximum-intensity-projection image obtained from three-dimensional spoiled gradientecho gadolinium-enhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20°) shows two left renal arteries (arrow head) and dominant right renal artery (thin arrow) with small right capsular branch (thick arrow).

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Table 3: Types of concordant renal anomalies detected by MRA.

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The vascular arterial anomaly may be unila­teral (right or left) or bilateral [Table 4] and [Figure 2], [Figure 3], [Figure 4], [Figure 5].
Table 4: Anomaly side detected by MRA in concordant cases.

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[Table 5] shows venous anomalies detected by MRA, while [Table 6] shows concordance and discordance between MRA and surgery regar­ding these anomalies.
Table 5. Venous anomalies.

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Table 6: Concordance and disconcordance of MRA and surgery regarding venous anomalies.

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[Figure 6] shows initial MRA misinterpretation of dual arterial supply of the left kidney, when in fact there was an early venous opacification of the retroaortic component of the left renal vein.
Figure 6: A 35-year-old male potential donor whose preoperative MRA was misinterpreted. Coronal source data images obtained from MRA (TR/TE, 5.0/2.0; flip angle, 20°). The reconstructed images were initially interpreted as showing single renal artery bilaterally. However, at blinded retrospective analysis of source data images, dual renal artery on the right side (transverse arrow) was detected.

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Regarding arterial anomalies, MRA has a sen­sitivity of 89.3% and specificity of 94.0%, with an accuracy of 90.8%.

For all venous anomalies, MRA has a sensi­tivity of 98.5% and specificity of 100% for all, with an accuracy of 98.6%.


   Discussion Top


Before donor nephrectomy, an accurate and effective preoperative renal vascular evalua­tion is necessary, and anything short of this can lead to surgical complications and injury to the patient or the organ being harvested. The radiologic evaluation of potential renal donors seeks to identify parenchymal abnor­malities and to serve as an anatomic road map of the vascular and urinary systems. [7]

In the past, urography or ultrasonography (US) was used to evaluate for renal masses and stones and ureteral anatomy, and an arterio­gram was obtained to identify the number, position, and patency of the renal arteries, as well as to determine the presence of proximal branches of the main renal artery. [1]

These imaging techniques have been supplan­ted largely by CT or MRA. Replacing both ar­teriography and urography or US with a single CT or MR examination provides a less costly and less invasive evaluation of donor kidneys. [1]

MRA has been used as a minimally invasive means of preoperative radiologic evaluation of renal donors. Earlier reports involving phase­contrast MR angiographic evaluation of the kidneys questioned its accuracy and thus its effectiveness. [8],[9],[10]

MRA is an attractive choice compared with other modalities used for renal imaging be­cause of its minimal invasiveness; further, it is an outpatient-based procedure, uses non-neph­rotoxic contrast material and has no radiation. [11]

Comparison of CT angiography with MRA using these earlier techniques found CT to have higher accuracy. [12],[13],[14] However, recent studies with gadolinium-enhanced MRA have established it as an accurate imaging modality for the visualization and evaluation of living renal donors for open nephrectomy. [3],[4],[5]

Recent studies have found gadolinium-en­hanced MRA to have high rates of accuracy and to be comparable to conventional angio­graphy and CT angiography in the evaluation of living renal donors for open neph-rectomy. [7]

Buzzas et al [4] determined gadolinium-enhanced MRA to be 100% accurate in evaluating the renal vascular anatomy in 15 patients for open nephrectomy. In a study by Low et al, [3] 22 pa­tients were evaluated with gadolinium-enhanced MRA and the results were compared with those obtained during conventional angiogra­phy and open nephrectomy. They also found 100% accuracy in identifying the renal arteries in all patients.

Bakker et al [15] have also described the advan­tage of gadolinium-enhanced MRA in a study of 24 living renal donors, with 100% accuracy in the detection of main and accessory renal arteries.

Our study shows the capability of gadoli­nium-enhanced MRA in assessment of the arterial and venous anatomy with a high level of accuracy in patients who are candidates for nephrectomy. Regarding arterial anomalies, MRA had a sensitivity of 89.3% and specifi­city of 94.0%, with an accuracy of 90.8%. For all venous anomalies, MRA had a sensitivity of 98.5% and specificity of 100%, with an accuracy of 98.6%.

Furthermore, patients tolerated the procedure well, and it is convenient to schedule them for this minimally invasive outpatient test rather than conventional angiography and excretory urography.

Not only this, but also our surgeons have found the anatomic detail provided by MRI to be satisfactory for selection of the site for har­vest. The MR angiographic images are presen­ted in a format similar to conventional angio­graphy, with multiplanar reconstruction images also available to show complex anatomy.

Information about a suspected early extrahilar branch can prove valuable to the transplan­tation surgeon in harvesting and the possible number of anastomoses required. [7]

In one of our patients, MRA exhibited an early extrahilar renal artery branch which was seen as two separate renal artery ostia at neph­rectomy, although from a clinical point of view it had no influence.

In two other patients, accessory arteries were missed on MRA but seen at DSA and surgery. Review of these images revealed the tiny ves­sels, but visualization of their exact relation­ship to the renal parenchyma was difficult des­pite multiplanar reformatting. These cases show the limitations of spatial resolution and the im­portance of optimizing imaging parameters as well as studying source data images [Figure 6].

In the fourth patient, the initial MRA was misinterpreted as showing dual arterial supply of the left kidney, when in fact there was an early venous opacification of the retroaortic component of the left renal vein [Figure 7]. To avoid such misinterpretation, studying all MRA phases is necessary.
Figure 7: Retroaortic left renal vein in a 41-year old man. Maximum-intensity-projection image from equilibrium-phase three-dimensional spoiled gradient-echo gadolinium-enhanced MR angiogram (TR/TE, 5.0/2.0; flip angle, 20º) shows a retroaortic left renal vein (arrow) which was misinterpreted as showing dual arterial supply of the left kidney, when in fact there was early venous opacification of the retroaortic component of the left renal vein.

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In the fifth case, MRA showed dual renal artery originating from aorta, while at surgery one of them was originating from inferior me­senteric artery.

In conclusion, renal MRI with gadolinium­enhanced MRA is an accurate and minimally invasive technique for obtaining a complete preoperative evaluation of renal donors. It has advantages over other means of evaluation. Further, it provides the necessary detail to allow harvest-site selection for donor nephrectomy.

Further experience with optimizing imaging techniques should continue to improve accu­racy rates of gadolinium-enhanced MR angio­graphy in preoperative assessment. [16]

 
   References Top

1.Halpern EJ, Mitchell DJ, Wechsler RJ, et al. Preoperative evaluation of living renal donors: Comparison of CT angiography and MR angiography. Radiology 2000;216:434-9.  Back to cited text no. 1
    
2.Neimatallah MA, Dong Q, Schoenberg SO, Cho KJ, Prince MR. Magnetic Resonance Imaging in renal transplantation. J Magn Reson Imaging 1999;10:357-68.  Back to cited text no. 2
[PUBMED]  [FULLTEXT]  
3.Low RN, Martinez AG, Steinberg SM, et al. Potential renal transplant donors: Evaluation with Gadolinium-enhanced MR angiography and MR urography. Radiology 1998;207:165-72.  Back to cited text no. 3
[PUBMED]  [FULLTEXT]  
4.Buzzas GR, Shield CF, Pay NT, Neuman MJ, Smith JL. Use of gadolinium-enhanced, ultra­fast, three-dimensional, spoiled gradient-echo magnetic resonance angiography in the pre­operative evaluation of living renal allograft donors. Transplantation 1997;27:1734-7.  Back to cited text no. 4
    
5.Nelson HA, Gilfeather M, Holman JM, Nelson EW, Yoon HC. Gadolinium-enhanced breath hold three-dimensional time-of-flight renal MR angiography in the evaluation of potential renal donors. J Vase Interv Radiol 1999;10:175-81.  Back to cited text no. 5
    
6.Lemke U, Taupitz M, Kluner C, et al. Pre­operative imaging in 78 living kidney donors using CE-MRA and DSA. Clin Transplant 2008;180(l):48-54  Back to cited text no. 6
    
7.Jha RC, Korangy SJ, Ascher SM, Takahama J, Kuo PC, Johnson LB. MR Angiography and Preoperative evaluation for laparoscopic donor nephrectomy. AJR Am J Roentgenol 2002; 178:1489-95.  Back to cited text no. 7
[PUBMED]  [FULLTEXT]  
8.Gourlay WA, Yucel EK, Hakaim AG, et al. Magnetic resonance angiography in the eva­luation of living related renal donors. Trans­plantation 1995;60:1363-6.  Back to cited text no. 8
    
9.Meyers SP, Talagala SL, Totterman S, et al. Evaluation of the renal arteries in kidney do­nors: Value of three-dimensional phase- con­trast MR angiography with maximum-inten­sity-projection or surface rendering. AJR Am J Roentgenol 1995;164:117-21.  Back to cited text no. 9
[PUBMED]  [FULLTEXT]  
10.Debatin JF, Sostman HD, Knelson M, Arga­bright M, Spritzer CE. Renal magnetic reso­nance angiography in the preoperative detec­tion of super-numerary renal arteries in poten­tial kidney donors. Invest Radiol 1993;28:882­-9.  Back to cited text no. 10
    
11.Kim JC, Kim CD, Jang MH, et al. Can mag­netic resonance angiogram be a reliable alter­native for donor evaluation for laparoscopic nephrectomy? Clin Transplant 2008;180(l):48-­54.  Back to cited text no. 11
    
12.Toki K, Takahara S, Kokado TY, et al. Com­parison of CT angiography with MR angio­graphy in the living renal donor. Transplant Proc 1998;30:2998-3000.  Back to cited text no. 12
    
13.Tsuda K, Murakami T, Kim T, et al. Helical CT angiography of living renal donors: Compa­rison with 3D Fourier transformation phase contrast MRA. J Comput Assist Tomogr 1998; 22:186-93.  Back to cited text no. 13
[PUBMED]  [FULLTEXT]  
14.Del Pizzo JJ, Sklar GN, You-Cheong JW, Levin B, Krebs T, Jacobs SC. Helical compu­terized tomography arteriography for evalua­tion of live renal donors undergoing laparos­copic nephrectomy. J Urol 1999;162:31-4.  Back to cited text no. 14
[PUBMED]  [FULLTEXT]  
15.Bakker J, Lightenberg G, Beek FJ, van Reedt Dortland RW, Hene RJ. Preoperative evalua­tion of living renal donors with gadolinium­enhanced magnetic resonance angiography. Transplantation 1999;67:1167-72.  Back to cited text no. 15
    
16.Glockner JF, Three-dimensional Gadolinium­enhanced MR Angiography: Applications for Abdominal Imaging. Radiographics 2001;21: 357-70.  Back to cited text no. 16
    

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Correspondence Address:
Abdelhady Taha Emam
Department of Radiology, Cairo University, Cairo
Egypt
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PMID: 21422618

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