NDT Advance Access published online on June 27, 2008
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfn358
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Increased peak systolic velocity in the renal artery of paediatric kidneys transplanted to adult recipients
1 Department of Radiology 2 Surgical Department, Section of Transplant Surgery 3 Medical Department, Section of Nephrology, Rikshospitalet University Hospital, 0027 Oslo, Norway
Correspondence and offprint requests to: Anne Gunther, Department of Radiology, Rikshospitalet University Hospital, N-0027 Oslo, Norway. Tel: +47-23070000; Fax: +47-23072610; E-mail: anne.gunther{at}rikshospitalet.no
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Abstract |
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Background. Paediatric kidneys transplanted to adult recipients increase in size after transplantation. It is unknown if the renal artery diameter increases concomitantly with the kidney. This study was performed to assess if peak systolic velocity (PSV) in the renal arteries of paediatric kidneys transplanted to adult recipients is comparable to PSV in the renal arteries of adult kidneys transplanted to adult recipients.
Subjects and methods. Fifteen adult patients with paediatric renal transplants were examined with ultrasound Doppler and compared with a control group of adult recipients with adult transplants. MR angiography (MRA) or intra-arterial angiography (IA) was performed in patients with elevated PSV. MRA renal diameters of the paediatric transplants were compared with adult transplants.
Results. The mean maximum PSV of the paediatric kidneys was 2.0 m/s (0.9–3.8), almost twice compared with the adult grafts transplanted to adult recipients, 1.1 m/s (0.7–1.6), P < 0.001. Seven paediatric transplants had a PSV >1.8 m/s, but only two had significant stenosis on MRA/IA. All patients had excellent blood pressure and renal function. The mean diameter of the paediatric renal arteries was 4.1 mm (3.4–6.0), whereas the mean for the adult renal arteries was 5.6 mm (4.8–6.9), P = 0.02.
Conclusion. Adult recipients of paediatric kidneys have significantly higher maximum PSV in the renal artery compared to adult recipients of adult grafts. The significantly smaller renal artery diameter might explain the high PSV. A PSV >1.8 m/s by itself does not necessarily indicate transplant renal artery stenosis in paediatric kidneys transplanted to adult recipients, but should be related to clinical findings.
Keywords: paediatric kidney; peak systolic velocity; renal transplant; transplant renal artery stenosis
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Introduction |
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There is increasing evidence that kidneys from diseased paediatric donors can be successfully transplanted to adult recipients [1–4] when no suitable child recipient is available. We have previously shown that paediatric kidneys transplanted to adults have a substantial growth potential [5]. It is also unknown if an increased peak systolic velocity (PSV) indicates the presence of significant transplant renal artery stenosis (TRAS) in a paediatric kidney transplanted to an adult.
Development of TRAS is a potential remediable cause of graft dysfunction and graft loss. The reported incidence of TRAS ranges from 1 to 23% in adult recipients receiving an adult graft [6], reflecting considerable heterogeneousity in patient material and/or investigational methods. Ultrasound Doppler is the first-line modality to assess the renal artery for TRAS [7–10]. Controversy exists regarding the threshold PSV value that should initiate further investigations to elucidate a diagnosis of TRAS, varying from 1.5 to 3.0 m/s [11]. A recent article proposed a PSV threshold of 1.8 m/s [12].
This study was initiated to evaluate PSV in an adult cohort that had received a renal transplant from paediatric donor more than 5 years earlier. A matched control group of adult patients receiving kidneys from adult donors 5–9 years earlier was also assessed. To verify if a finding of elevated PSV >1.8 m/s represented TRAS, contrast-enhanced 3D MR angiography (MRA) or intra-arterial angiography (IA) with pressure measurement was performed. The MRA diameter of the paediatric renal arteries was compared to the diameter found in a control group of adult transplant arteries.
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Subjects and methods |
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Patients
From 1998 to 2001, a total of 19 patients (11 men and 8 women) were prospectively included in a previously published study [5]. All received their first renal transplant. The organs were allocated according to standard criteria, e.g. ABO compatibility, HLA A, B and DR mismatches and time on the waiting list. All patients were panel reactive antibody (PRA) negative. Kidney grafts from donors aged <2 years, weighting 9–12 kg, were transplanted en bloc to one recipient. All kidneys were transplanted using a standard technique with the vessels anastomosed to the external iliac artery and vein.
The patients were contacted and invited to a re-examination 5–9 years after transplantation. Fifteen of the 19 patients from the cohort were available for the long-term follow-up. Four patients were not included: one had died without functioning graft due to polyomavirus infection, one was on dialysis, one patient was in a nursing home and one patient did not want to participate. A total of 19 paediatric kidney grafts (11 patients with single kidneys and 4 patients with two kidneys transplanted en bloc) were examined. All patients had excellent blood pressure and renal function. Demographic data are presented in Table 1.
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A control group of 12 renal transplant recipients having received an adult graft from a deceased donor was randomly selected to match the paediatric transplant recipients for plasma creatinine, blood pressure and time since transplantation. In addition, MRAs from 12 random patients were used as a reference material for renal artery diameter of adult kidneys transplanted to adult recipients.
Ultrasound Doppler, MRA and angiography
The kidney transplants were examined with ultrasound Doppler (Acuson Sequoia(TM), Siemens, Mountain View, CA, USA) using a 1–4 MHz curved-array transducer (4C1) or a 1–4 MHz vector transducer (4V1). Angle-corrected PSV was measured with short intervals through the length of the renal artery(ies), and if present, through the length of the donor aorta. The highest PSV value measured in each patient was reported as maximum PSV. All examinations were performed by the same radiologist (A.G.).
If PSV exceeded 1.8 m/s, the patient underwent a contrast-enhanced 3D MRA or an IA with pressure measurement (one patient with a stent in the renal artery) to determine if the elevated PSV represented a significant TRAS. In addition, the diameter of the renal artery(ies) was measured at three locations: the origin of the artery, the middle part and the branching point of the artery. A mean of each artery's three diameters was calculated. Stenotic areas of the arteries were not included. The same measurements were done in 12 random MRAs of adult renal kidneys transplanted to adult recipients.
The MRA exams were performed with a 1.5 T MR imaging system (Avanto, Siemens, Erlangen, Germany) using a spoiled gradient echo sequence with TR/TE of 2.53/1.03 ms, slice thickness 1.0 mm and no interslice gap. Image subtraction was used.
Statistical methods
Data are expressed as mean and range. P < 0.05 was considered statistically significant. For comparisons of the groups, the Mann–Whitney–Wilcoxon test was performed. All statistical analyses were calculated using SPSS statistical software (SPSS 13, Inc., Chicago, IL, USA).
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Results |
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The mean maximum PSV for the paediatric transplants was 2.0 m/s (0.9–3.8), which was almost twice the mean value of 1.1 m/s (0.7–1.6) for the adult transplants, P < 0.001 (Figure 1). Seven of the 15 patients (47%) in the paediatric group had a maximum PSV exceeding 1.8 m/s. Four patients (27%) had a PSV
2.5 m/s. None of the patients in the control group had maximum PSV exceeding 1.6 m/s.
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The seven paediatric patients who had PSV exceeding 1.8 m/s were further examined with MRA (n = 6) or IA (n = 1) according to the protocol. Three patients had PSV > 1.8 and <2.5 m/s, but only non-significant stenosis (lumen diameter reduction <50%) was demonstrated on MRA. Four patients had a PSV
2.5 m/s. Two of these (PSV of 2.6 and 3.8 m/s) had a significant stenosis (lumen diameter reduction 50%) verified with MRA or angiography with pressure measurement. The other two (PSV of 2.5 and 2.8 m/s) had normal renal arteries on MRA. One recipient had maximum PSV measured close to a sharp bend in the renal artery, while the other had high velocities throughout the length of the renal artery, as well as the external iliac artery. The anatomic location where the maximum PSV was measured varied, at the anastomosis of the transplanted renal artery to the external iliac artery (n = 4), at a kink of the renal artery (n = 2) or at the origin of renal artery from donor aorta (no anastomosis) (n = 1).
The mean renal artery diameter of the seven paediatric grafts who underwent MRA was 4.1 mm (3.4–6.0), whereas the mean for the reference group of adult renal transplant arteries was 5.6 mm (4.8–6.9), P = 0.02.
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Discussion |
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The main finding of this study was that adult recipients of paediatric kidneys have a significantly higher maximum PSV in their transplant artery compared to adult recipients of adult grafts. Controversy exists regarding the optimal PSV cut-off value for suspecting a significant TRAS. A recent article proposed a PSV threshold of 1.8 m/s [12]. However, the reference values used are based on experience with adult kidney grafts transplanted into adult recipients. In this long-term follow-up of adults with paediatric kidney transplants, nearly half of the patients (47%) had a PSV >1.8 m/s, which for adult kidneys indicates TRAS. Only two patients had significant artery stenosis on MRI or IA, and both had a PSV >2.5 m/s. Moreover all patients had excellent blood pressure and renal function despite findings of elevated PSV. Further studies including patient with clinical findings of significant TRAS need to be performed in order to indicate an optimal PSV threshold for suspecting TRAS in paediatric kidneys transplanted to adult recipients.
A possible explanation for the high PSV is a smaller growth potential for the grafted artery than for the parenchymal part of the transplanted kidney, and the disproportionate size of the main renal arterial segments in relation to an enlarged peripheral vascular bed results in increased blood velocities, without necessarily substantiating a clinical relevant TRAS. Due to lack of data in the literature on the lumen diameter of adult transplant arteries, we compared the results of the paediatric MRAs with 12 random MRAs of adult patients who had received adult transplants. The significantly smaller lumen diameter found in the paediatric renal arteries indicate that there actually is less growth potential for the grafted paediatric artery than for the parenchymal part of the transplanted kidney. Unfortunately we have no earlier PSV measurements available for comparison, which could have demonstrated a change in PSV in parallel with the increase in kidney size.
In conclusion, adult recipients of paediatric kidneys have a significantly higher maximum PSV in their transplant artery compared to adult recipients of adult grafts. This is most likely due to a smaller renal artery diameter in the paediatric transplants. Ultrasound Doppler alone is therefore not adequate for diagnosing TRAS in this population. Clinical suspicion of TRAS with an unexplained increase in creatinine and/or systemic blood pressure is pivotal and should be confirmed with Doppler ultrasound using a high PSV threshold, prompting MRA or angiography.
The authors would like to thank Professor H.-J. Smith for interpreting the MRA examinations.
Conflict of interest statement. None declared.
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References |
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TopAbstractIntroductionSubjects and methodsResultsDiscussionReferences |
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- Dharnidharka VR, Stevens G, Howard RJ. En-bloc kidney transplantation in the United States: an analysis of united network of organ sharing (UNOS) data from 1987 to 2003. Am J Transplant (2005) 5:1513–1517.[CrossRef][Web of Science][Medline]
- Foss A, Gunther A, Line PD, et al. Long-term clinical outcome of paediatric kidneys transplanted to adults. Nephrol Dial Transplant (2008) 23:726–729.
[Abstract/Free Full Text] - Pelletier SJ, Guidinger MK, Merion RM, et al. Recovery and utilization of deceased donor kidneys from small pediatric donors. Am J Transplant (2006) 6:1646–1652.[CrossRef][Web of Science][Medline]
- Sureshkumar KK, Reddy CS, Nghiem DD, et al. Superiority of pediatric en bloc renal allografts over living donor kidneys: a long-term functional study. Transplantation (2006) 82:348–353.[Web of Science][Medline]
- Foss A, Line PD, Brabrand K, et al. A prospective study on size and function of paediatric kidneys (<10 years) transplanted to adults. Nephrol Dial Transplant (2007) 22:1738–1742.
[Abstract/Free Full Text] - Fervenza FC, Lafayette RA, Alfrey EJ, et al. Renal artery stenosis in kidney transplants. Am J Kidney Dis (1998) 31:142–148.[CrossRef][Web of Science][Medline]
- Bruno S, Ferrari S, Remuzzi G, et al. Doppler ultrasonography in posttransplant renal artery stenosis: a reliable tool for assessing effectiveness of revascularization? Transplantation (2003) 76:147–153.[CrossRef][Web of Science][Medline]
- de Morais RH, Muglia VF, Mamere AE, et al. Duplex Doppler sonography of transplant renal artery stenosis. J Clin Ultrasound (2003) 31:135–141.[CrossRef][Web of Science][Medline]
- O’Neill W, Baumgarten D. Ultrasonography in renal transplantation. Am J Kidney Dis (2002) 39:663–678.[CrossRef][Web of Science][Medline]
- Wong W, Fynn SP, Higgins RM, et al. Transplant renal artery stenosis in 77 patients—does it have an immunological cause? Transplantation (1996) 61:215–219.[CrossRef][Web of Science][Medline]
- Loubeyre P, Abidi H, Cahen R, et al. Transplanted renal artery: detection of stenosis with color Doppler US. Radiology (1997) 203:661–665.
[Abstract/Free Full Text] - Bruno S, Remuzzi G, Ruggenenti P. Transplant renal artery stenosis. J Am Soc Nephrol (2004) 15:134–141.
[Abstract/Free Full Text]
Accepted in revised form: 2. 6.08
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