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Duplex Doppler ultrasound for detection of significant renal artery stenosis in transplant kidney with end to side arterial anastomosis
Clinical Queries: Nephrology 5 (2016) 37–39
Contents lists available at ScienceDirect
Clinical Queries: Nephrology journal homepage: www.elsevier.com/locate/cqn
Original article
Duplex Doppler ultrasound for detection of significant renal artery stenosis in transplant kidney with end to side arterial anastomosis Shruti Gandhi a,*, Kajal Patel a, Vivek Kute b, Maulik Mehta c a
Department of Radiology & Imaging, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre (IKDRC), Dr. H.L. Trivedi Institute of Transplantation Sciences (ITS), Civil Hospital Campus, Asarwa, Ahmedabad 380016, Gujarat, India b Department of Nephrology, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre (IKDRC), Dr. H.L. Trivedi Institute of Transplantation Sciences (ITS), Civil Hospital Campus, Asarwa, Ahmedabad 380016, Gujarat, India c Orthokid Hospital, Drive in Road, Ahmedabad, India
A R T I C L E I N F O
A B S T R A C T
Article history: Received 4 July 2016 Accepted 10 July 2016 Available online 14 November 2016
Objective: To evaluate the accuracy of velocity parameters and to define optimum threshold values of these parameters in detection of >60% renal artery stenosis in patients with end to side arterial anastomosis. Methods: The study group composed of 17 patients of transplant renal artery stenosis confirmed by CT angiography; and 25 control patients with normal Doppler study. Doppler parameters like PSV in main transplanted renal artery, PSV in interlobar artery, PSV in iliac artery, acceleration time, and resistive index were evaluated. Pre-PSV ratio and Post-PSV ratio were calculated. Patients were divided into group A (>60% stenosis) and B (<60% stenosis) according to CT angiography reports. Control group assigned as group C. Difference between Doppler parameters were evaluated by individual t test. Receiver operating curve was performed to determine optimal parameter for diagnosis of >60% stenosis. Results: Considering better sensitivity and specificity for diagnosis of >60% stenosis the best threshold for Intrarenal RI, acceleration time, PSV, Pre-PSV ratio and Post-PSV ratio were determined to be 0.058, 0.071 s, 3.1 m/s, 2 and 10 respectively. P value of acceleration time between group B and C; and P value of PSV in main renal artery, Pre-PSV ratio and Intrarenal RI between group A and B is >0.05. Conclusion: Post-PSV ratio is the best parameter for diagnosis of significant stenosis and its optimum threshold value is 10. ß 2016 Published by Elsevier, a division of RELX India, Pvt. Ltd.
Keywords: Doppler ultrasound Transplant renal artery stenosis (TRAS) CT angiography
1. Introduction Renal artery stenosis (RAS) is one of the most important complications in kidney transplantation with incidence ranging from 1.6% to 16%.1 It is important to identify as it can be corrected with surgical or radiological intervention reducing blood pressure and avoiding graft failure.2 End to end anastomosis have threefold higher risk of developing stenosis than end to side anastomosis.3,4 Patients with less than 60% stenosis can be managed conservatively
Abbreviations: MDCT, multi-detector computed tomography; PSV, peak systolic velocity; DSA, digital subtraction angiography; RI, resistive index; TRAS, transplant renal artery stenosis; RAS, renal artery stenosis. * Corresponding author at: 13-Vrundavan Apartment, Plot no 7 Laxminarayan Society, Near Shantinagar Jain temple, Usmanpura, Ahmedabad 380013, Gujarat, India. E-mail addresses: [email protected] (S. Gandhi), [email protected] (K. Patel), [email protected] (V. Kute), [email protected] (M. Mehta). http://dx.doi.org/10.1016/j.cqn.2016.07.004 2211-9477/ß 2016 Published by Elsevier, a division of RELX India, Pvt. Ltd.
with close follow up. Doppler ultrasound (DUS) is a non-invasive method that provides information regarding kidney morphology and hemodynamic changes.5 A variety of Doppler parameters have been evaluated for diagnosis of renal artery stenosis in transplanted patients. 1.1. Objective To evaluate the accuracy of velocity parameters and to define optimum threshold values of these parameters in detection of >60% renal artery stenosis in patients with end to side arterial anastomosis. 2. Materials and methods After ethical committee’s approval, a retrospective analysis study was done on data of recorded Doppler parameters during the period of January 2010 to December 2013. The study group was composed of 17 living related transplant patients with known
S. Gandhi et al. / Clinical Queries: Nephrology 5 (2016) 37–39
38
Units Acceleration time seconds (s) Peak systolic velocity meter per second (m/s)
Transplant Renal Artery Stenosis while control group was composed of 25 renal transplant patients with good posttransplant course, normal serum creatinine value, diastolic blood pressure of 90 mmHg or less, and were taking only one or no antihypertensive drug. Doppler study in this group was done at 3 months of transplantation. In our study the ACUSON X500 of Siemens Medical Solutions USA, ultrasound system was used to study following parameters; peak systolic velocity (PSV) in main renal artery, PSV in interlobar artery, PSV in iliac artery, acceleration time, and resistive index (RI). Doppler study was done by radiologist from our institute with more than 5 years of experience. 3.5–5.0 MHz transducer was used. The area of the greatest PSV was recorded in main renal artery. Angle of insonation was set at 60 degree or less. RI, acceleration time and PSV of the interlobar arteries were measured at upper, mid and lower poles of the allograft in all the patients. The average value of each parameter was calculated and recorded as intra renal RI, acceleration time and inter lobar PSV. Pre-PSV ratio (ratio of PSV in renal artery to iliac artery) and Post-PSV ratio (ratio of PSV in main renal artery to interlobar artery) was calculated following the Doppler study. Patients who had other than end to side anastomosis with external iliac artery were excluded from the study. The patients who had stenosis of main renal artery were subjected for CT angiography study on Somatom sensation 64 CT scan from Siemens using non-ionic contrast Iomeron 350 mg/dl within a week after Doppler study. CT reported by the radiologist who blinded to Doppler report. The patients were divided into group A and B according CT report. Patients with more than 60% stenosis on CT angiography were included in group A. Patients with less than 60% stenosis was included in group B. Control group includes 25 patients with good transplantation course classified as group C. To evaluate difference between two Doppler parameters individual t test was used. Values were expressed as Mean SD. P value < 0.05 was considered as statistically significant. Receiver operating characteristic curves were performed to determine optimal parameter for diagnosis of >60% (significant) renal artery stenosis.
Table 1 Mean SD of Doppler parameters of all three groups. Variables PSV in RA (m/sec) Intrarenal RI Acceleration time (seconds) Pre-PSV ratio Post-PSV ratio
Group A (n = 10) *
Group B (n = 7) v
Group C (n = 25)
4.355 0.725 0.53 0.052@ 0.0852 0.008
%$4.114 0.697 0.56 0.04# 0.069 0.008$
2.18.64 0.421*, 0.67 0.047#@ 0.066 0.004%
2.77 0.48^ t 17.49 7.87!,
2.55 0.34& rt 9.24 0.79 ,
1.65 0.23&^ r 4.97 1.86?,
v
t
P*, P&, P^, P%, P#, P@, P!, P = <0.0001; P$ = 0.0016; P
v
r
0.0157; P = 0.04.
Table 2 Sensitivity and specificity for diagnosis of significant renal artery stenosis using cut off value.
Intrarenal RI 0.58 Acceleration time > 0.071 PSV > 3.1 m/s Pre-PSV ratio 2.0 Post-PSV ratio > 10
Sensitivity
Specificity
90 100 100 100 100
81.2 90.62 78.1 75.0 93.7
Table 3 Detection of >60% stenosis using post-PSV ratio at various threshold value.
Post-PSV > 10 Post-PSV > 10.2 Post-PSV > 10.3
Sensitivity
Specificity
100 90 90
93.75 96.87 100
3. Results Mean age of patients for stenotic group is 29.5 years. Mean age of patients for non-stenotic group is 31 years. M:F ratio is 7.2. Out of 17 patients who had stenosis of main renal artery; 7 had <60% (non-significant) stenosis and 10 had 60% (significant) stenosis on CT angiography. There was no complete occlusion of main renal artery in any patient. Statistical results are shown in Table 1. Intrarenal RI, PSV in main renal artery and pre-PSV ratio shows statistically significant difference (P*, Pw, P#, P@, P&, P^) between stenotic (groups A & B) and non-stenotic group (group C). There was no significant difference found between group A and group B using these parameters. Acceleration time and post-PSV ratio are significantly different (P$, PT) between group A and B; and group A and C. Acceleration time shows no significant difference between group B and group C. The post-PSV ratio is only parameters which shows statistically significant difference (P!, PT, PP) between all three groups. Considering better sensitivity and specificity for diagnosis of >60% stenosis the best threshold for intrarenal RI, acceleration time, PSV, pre-PSV ratio and post-PSV ratio were determined to be 0.58, 0.071 s, 3.1 m/s, 2 and 10 respectively. Sensitivity and
Fig. 1. Receiver operating characteristic curves for intrarenal RI, acceleration time, PSV in renal artery, pre-PSV ratio and post-PSV ratio in detection of significant (60%) TRAS.
specificity for the same are shown in Table 2. The diagnostic efficiency of the post-PSV ratio at various threshold values are shown in Table 3. Receiver operating characteristic curves showed that the post-PSV ratio is the optimal velocity parameter for diagnosis of transplant renal artery stenosis (TRAS) > 60% (Fig. 1). The area under the receiver operating curve for post PSV ratio (0.995) is significantly greater than that of intrarenal RI (0.902) (P < 0.040) and pre-PSV ratio (0.914) (P < 0.047); and nonsignificantly greater than that of acceleration time (0.953) and PSV in main renal artery (0.913). 4. Discussion The definition of thermodynamically significant transplant renal arterial stenosis (TRAS) has not been standardized6; but it is considered significant if more than 60%.7,8 The gold standard for
S. Gandhi et al. / Clinical Queries: Nephrology 5 (2016) 37–39
diagnosis of transplant renal artery stenosis is angiography. Duplex-Doppler examination, performed by an experienced operator, is an invaluable tool for the diagnosis of TRAS. End to end anastomosis have threefold higher risk of developing stenosis than end to side anastomosis3,4; our study includes only patients with end to side anastomosis and these could be the reason for small sample size. In our study 15 patients of TRAS were presented to institute within first 6 months of renal transplantation while only two patients had delayed presentation between 15th and 20th months of post-transplantation. Therefore, Doppler study of 25 patients with good transplantation course (control group) was done at 3 months of post-transplant period. We excluded first 10 post-transplant days to avoid factors like postoperative edema. Controversy exists regarding the optimal PSV cut-off value for suspecting a significant TRAS. Transplant arteries are typically much more tortuous than native renal arteries. This makes the setting of accurate angle correction on spectral Doppler more difficult. The measurement of renal artery PSV played an important role as it is also applied to calculate velocity ratio parameters. We obtained correct angle of insonation that in all instance below 60 degree. Sample gate is placed at most stenotic site and greatest PSV was recorded. Several investigators have demonstrated that using PSV values of 1.8–2.0 m/s as a criterion for the presence of a significant renal artery stenosis, sensitivities of 88–98% and specificities of 62–98% have been achieved.9–11 Baxter et al. used a peak systolic velocity of 2.5 m/s in the transplant renal artery which showed a sensitivity of 100% and a specificity of 95% for detection of renal artery stenosis.12 We found 12.9% higher specificity when we increase threshold of PSV from 2.5 m/s to 3.1 m/s. Our findings are in accordance with Patel et al. which also state that absolute renal artery velocity 2.5 m/s is a limited surrogate marker for significant renal artery stenosis and 3.0 m/s is a better choice.13 We found post-PSV ratio is potential best velocity parameter for diagnosis of significant stenosis. Pre-PSV and post-PSV ratio reflects hemodynamic changes in blood flow velocity and can reduce or eliminate inter individual variations in measurement of renal artery PSV. De Morais et al. found pre-PSV ratio > 1.8 is one of the most accurate parameters in diagnosing TRAS.14 We found threshold of >2.0 for the same. PSV in iliac artery can be affected by aortoiliac or lower extremity vascular disease; while renal artery PSV increases and interlobar artery PSV decreases with the increasingly severity of stenosis.15 This implies that the postPSV ratio is better than pre-PSV ratio for diagnosis of significant RAS. Li et al. found threshold of 5 to diagnosis of more than 50% stenosis in native kidney.15 Li et al. found threshold of 13 for diagnosis of severe (80–90%) stenosis in transplant kidney.16 Their study included 16 patients of TRAS confirmed by DSA; 14 of them had end to end arterial anastomosis. No such cut off point is described in literature to our knowledge for diagnosis of significant (>60%) stenosis in transplant kidney in patients with end to side arterial anastomosis. We found post-PSV ratio is better than other parameters and its optimum threshold 10 for diagnosis of >60% stenosis. Saarinen et al. have shown that a low RI (<0.6) is highly suggestive of TRAS.17 One study showed the sensitivity of intrarenal RI in detecting TRAS was about 85% at cut off point of 0.55.18 We found threshold of <0.58 for the same. Acceleration time greater than 0.07 is used to define stenosis. We found acceleration time useful parameter for diagnosis of significant
39
stenosis but it is a poor predictor to diagnose non-significant stenosis, in accordance with Baxter et al. who also found acceleration time less useful as a discriminating diagnostic test to diagnose renal artery stenosis.12 Limitation of study was we did CT angiography of patients in whom Doppler findings of renal artery stenosis are present. We could not exclude the rare possibility of TRAS in the control group of patients with good transplantation course, normal serum creatinine and blood pressure. 5. Conclusion Post-PSV ratio is the most useful parameter for diagnosis of significant stenosis and to differentiating between significant and non-significant stenosis. Its optimum threshold value is 10. Acceleration time is found to be poor predictor to diagnose nonsignificant stenosis. PSV in main renal artery, pre-PSV ratio and intrarenal RI could not predict degree of stenosis. Conflicts of interest The authors have none to declare. Acknowledgment We are also thankful to our librarian Jyotsana Suthar for literature search and submission. References 1. Faenza A, Spolaore G. Renal artery stenosis after renal transplantation. Kidney Suppl. 1983;14:S54–S59. 2. Tublin ME, Dodd GD. Sonography of renal transplantation. Radiol Clin North Am. 1995;33:447–459. 3. Akbar SA, Jafri SZ, Amen Faenza A, et al. Renal artery stenosis after renal transplantation. Kidney Int Suppl. 1983;14:S54–S59. 4. Jordan ML, Cook GT, Cardella CJ. Ten years of experience with vascular complications in renal transplantation. J Urol. 1982;128:689–692. 5. O’neill DA. Ultrasonography in renal transplantation. Am J Kidney Dis. 2002; 39:663–678. 6. Patel NH, Jindal RM, Wilkin T, et al. Renal arterial stenosis in renal allografts: retrospective study of predisposing factors and outcome after percutaneous transluminalangioplasty. Radiology. 2001;219:663–667. 7. Grossman RA, Dafoe DC, Shoenfeld RB, et al. Percutaneous transluminal angioplasty treatment of renal transplant artery stenosis. Transplantation. 1982;34:339–343. 8. Lacombe M. Arterial stenosis complicating renal allotransplantation in man, a study of 38 cases. Ann Surg. 1975;181:328–330. 9. Olin JW, Piedmonte MR, Young JR, DeAnna S, Grubb M, Childs MB. The utility of duplex ultrasound scanning of the renal arteries for diagnosing significant renal artery stenosis. Ann Intern Med. 1995;122:833–838. 10. Strandness DE. Duplex imaging for the detection of renal artery stenosis. Am J Kidney Dis. 1994;24:674–678. 11. Hansen KJ, Tribble RW, Reavis SW, et al. Renal duplex sonography: evaluation of clinical utility. J Vasc Surg. 1990;12:227–236. 12. Baxter GM, Ireland H, Moss JG, et al. Colour Doppler ultrasound in renal transplant artery stenosis: which Doppler index? Clin Radiol. 1995;50:618–622. 13. Patel U, Khaw KK, Hughes NC. Doppler ultrasound for detection of renal transplant artery stenosis-threshold peak systolic velocity needs to be higher in a low-risk or surveillance population. Clin Radiol. 2003;58:772–777. 14. de Morais RH, Muglia VF, Mamere AE, et al. Duplex Doppler sonography of transplant renal artery stenosis. J Ultrasound. 2003;31:135–141. 15. Li J, Wang L, Jiang Y-x, et al. Evaluation of renal artery stenosis with velocity parameter of Doppler sonography. J Ultrasound Med. 2006;25:735–742. 16. Li JC, Ji ZG, Cai S, Jiang YX, Dai Q, Zhang JX. Evaluation of severe transplant renal artery stenosis with Doppler sonography. J Clin Ultrasound. 2005;33:261–269. 17. Saarinen O, Salmela K, Edgren J. Doppler ultrasound in the diagnosis of renal transplant artery stenosis-value of resistive index. Acta Radiol. 1994;35:586–589. 18. Ardalan MR, Tarzamani MK, Shoja MM. A correlation between direct and indirect Doppler ultrasonographic measures in transplant renal artery stenosis. Transplant Proc. 2007;39:1436–1438.
Contents lists available at ScienceDirect
Clinical Queries: Nephrology journal homepage: www.elsevier.com/locate/cqn
Original article
Duplex Doppler ultrasound for detection of significant renal artery stenosis in transplant kidney with end to side arterial anastomosis Shruti Gandhi a,*, Kajal Patel a, Vivek Kute b, Maulik Mehta c a
Department of Radiology & Imaging, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre (IKDRC), Dr. H.L. Trivedi Institute of Transplantation Sciences (ITS), Civil Hospital Campus, Asarwa, Ahmedabad 380016, Gujarat, India b Department of Nephrology, G. R. Doshi and K. M. Mehta Institute of Kidney Diseases and Research Centre (IKDRC), Dr. H.L. Trivedi Institute of Transplantation Sciences (ITS), Civil Hospital Campus, Asarwa, Ahmedabad 380016, Gujarat, India c Orthokid Hospital, Drive in Road, Ahmedabad, India
A R T I C L E I N F O
A B S T R A C T
Article history: Received 4 July 2016 Accepted 10 July 2016 Available online 14 November 2016
Objective: To evaluate the accuracy of velocity parameters and to define optimum threshold values of these parameters in detection of >60% renal artery stenosis in patients with end to side arterial anastomosis. Methods: The study group composed of 17 patients of transplant renal artery stenosis confirmed by CT angiography; and 25 control patients with normal Doppler study. Doppler parameters like PSV in main transplanted renal artery, PSV in interlobar artery, PSV in iliac artery, acceleration time, and resistive index were evaluated. Pre-PSV ratio and Post-PSV ratio were calculated. Patients were divided into group A (>60% stenosis) and B (<60% stenosis) according to CT angiography reports. Control group assigned as group C. Difference between Doppler parameters were evaluated by individual t test. Receiver operating curve was performed to determine optimal parameter for diagnosis of >60% stenosis. Results: Considering better sensitivity and specificity for diagnosis of >60% stenosis the best threshold for Intrarenal RI, acceleration time, PSV, Pre-PSV ratio and Post-PSV ratio were determined to be 0.058, 0.071 s, 3.1 m/s, 2 and 10 respectively. P value of acceleration time between group B and C; and P value of PSV in main renal artery, Pre-PSV ratio and Intrarenal RI between group A and B is >0.05. Conclusion: Post-PSV ratio is the best parameter for diagnosis of significant stenosis and its optimum threshold value is 10. ß 2016 Published by Elsevier, a division of RELX India, Pvt. Ltd.
Keywords: Doppler ultrasound Transplant renal artery stenosis (TRAS) CT angiography
1. Introduction Renal artery stenosis (RAS) is one of the most important complications in kidney transplantation with incidence ranging from 1.6% to 16%.1 It is important to identify as it can be corrected with surgical or radiological intervention reducing blood pressure and avoiding graft failure.2 End to end anastomosis have threefold higher risk of developing stenosis than end to side anastomosis.3,4 Patients with less than 60% stenosis can be managed conservatively
Abbreviations: MDCT, multi-detector computed tomography; PSV, peak systolic velocity; DSA, digital subtraction angiography; RI, resistive index; TRAS, transplant renal artery stenosis; RAS, renal artery stenosis. * Corresponding author at: 13-Vrundavan Apartment, Plot no 7 Laxminarayan Society, Near Shantinagar Jain temple, Usmanpura, Ahmedabad 380013, Gujarat, India. E-mail addresses: [email protected] (S. Gandhi), [email protected] (K. Patel), [email protected] (V. Kute), [email protected] (M. Mehta). http://dx.doi.org/10.1016/j.cqn.2016.07.004 2211-9477/ß 2016 Published by Elsevier, a division of RELX India, Pvt. Ltd.
with close follow up. Doppler ultrasound (DUS) is a non-invasive method that provides information regarding kidney morphology and hemodynamic changes.5 A variety of Doppler parameters have been evaluated for diagnosis of renal artery stenosis in transplanted patients. 1.1. Objective To evaluate the accuracy of velocity parameters and to define optimum threshold values of these parameters in detection of >60% renal artery stenosis in patients with end to side arterial anastomosis. 2. Materials and methods After ethical committee’s approval, a retrospective analysis study was done on data of recorded Doppler parameters during the period of January 2010 to December 2013. The study group was composed of 17 living related transplant patients with known
S. Gandhi et al. / Clinical Queries: Nephrology 5 (2016) 37–39
38
Units Acceleration time seconds (s) Peak systolic velocity meter per second (m/s)
Transplant Renal Artery Stenosis while control group was composed of 25 renal transplant patients with good posttransplant course, normal serum creatinine value, diastolic blood pressure of 90 mmHg or less, and were taking only one or no antihypertensive drug. Doppler study in this group was done at 3 months of transplantation. In our study the ACUSON X500 of Siemens Medical Solutions USA, ultrasound system was used to study following parameters; peak systolic velocity (PSV) in main renal artery, PSV in interlobar artery, PSV in iliac artery, acceleration time, and resistive index (RI). Doppler study was done by radiologist from our institute with more than 5 years of experience. 3.5–5.0 MHz transducer was used. The area of the greatest PSV was recorded in main renal artery. Angle of insonation was set at 60 degree or less. RI, acceleration time and PSV of the interlobar arteries were measured at upper, mid and lower poles of the allograft in all the patients. The average value of each parameter was calculated and recorded as intra renal RI, acceleration time and inter lobar PSV. Pre-PSV ratio (ratio of PSV in renal artery to iliac artery) and Post-PSV ratio (ratio of PSV in main renal artery to interlobar artery) was calculated following the Doppler study. Patients who had other than end to side anastomosis with external iliac artery were excluded from the study. The patients who had stenosis of main renal artery were subjected for CT angiography study on Somatom sensation 64 CT scan from Siemens using non-ionic contrast Iomeron 350 mg/dl within a week after Doppler study. CT reported by the radiologist who blinded to Doppler report. The patients were divided into group A and B according CT report. Patients with more than 60% stenosis on CT angiography were included in group A. Patients with less than 60% stenosis was included in group B. Control group includes 25 patients with good transplantation course classified as group C. To evaluate difference between two Doppler parameters individual t test was used. Values were expressed as Mean SD. P value < 0.05 was considered as statistically significant. Receiver operating characteristic curves were performed to determine optimal parameter for diagnosis of >60% (significant) renal artery stenosis.
Table 1 Mean SD of Doppler parameters of all three groups. Variables PSV in RA (m/sec) Intrarenal RI Acceleration time (seconds) Pre-PSV ratio Post-PSV ratio
Group A (n = 10) *
Group B (n = 7) v
Group C (n = 25)
4.355 0.725 0.53 0.052@ 0.0852 0.008
%$4.114 0.697 0.56 0.04# 0.069 0.008$
2.18.64 0.421*, 0.67 0.047#@ 0.066 0.004%
2.77 0.48^ t 17.49 7.87!,
2.55 0.34& rt 9.24 0.79 ,
1.65 0.23&^ r 4.97 1.86?,
v
t
P*, P&, P^, P%, P#, P@, P!, P = <0.0001; P$ = 0.0016; P
v
r
0.0157; P = 0.04.
Table 2 Sensitivity and specificity for diagnosis of significant renal artery stenosis using cut off value.
Intrarenal RI 0.58 Acceleration time > 0.071 PSV > 3.1 m/s Pre-PSV ratio 2.0 Post-PSV ratio > 10
Sensitivity
Specificity
90 100 100 100 100
81.2 90.62 78.1 75.0 93.7
Table 3 Detection of >60% stenosis using post-PSV ratio at various threshold value.
Post-PSV > 10 Post-PSV > 10.2 Post-PSV > 10.3
Sensitivity
Specificity
100 90 90
93.75 96.87 100
3. Results Mean age of patients for stenotic group is 29.5 years. Mean age of patients for non-stenotic group is 31 years. M:F ratio is 7.2. Out of 17 patients who had stenosis of main renal artery; 7 had <60% (non-significant) stenosis and 10 had 60% (significant) stenosis on CT angiography. There was no complete occlusion of main renal artery in any patient. Statistical results are shown in Table 1. Intrarenal RI, PSV in main renal artery and pre-PSV ratio shows statistically significant difference (P*, Pw, P#, P@, P&, P^) between stenotic (groups A & B) and non-stenotic group (group C). There was no significant difference found between group A and group B using these parameters. Acceleration time and post-PSV ratio are significantly different (P$, PT) between group A and B; and group A and C. Acceleration time shows no significant difference between group B and group C. The post-PSV ratio is only parameters which shows statistically significant difference (P!, PT, PP) between all three groups. Considering better sensitivity and specificity for diagnosis of >60% stenosis the best threshold for intrarenal RI, acceleration time, PSV, pre-PSV ratio and post-PSV ratio were determined to be 0.58, 0.071 s, 3.1 m/s, 2 and 10 respectively. Sensitivity and
Fig. 1. Receiver operating characteristic curves for intrarenal RI, acceleration time, PSV in renal artery, pre-PSV ratio and post-PSV ratio in detection of significant (60%) TRAS.
specificity for the same are shown in Table 2. The diagnostic efficiency of the post-PSV ratio at various threshold values are shown in Table 3. Receiver operating characteristic curves showed that the post-PSV ratio is the optimal velocity parameter for diagnosis of transplant renal artery stenosis (TRAS) > 60% (Fig. 1). The area under the receiver operating curve for post PSV ratio (0.995) is significantly greater than that of intrarenal RI (0.902) (P < 0.040) and pre-PSV ratio (0.914) (P < 0.047); and nonsignificantly greater than that of acceleration time (0.953) and PSV in main renal artery (0.913). 4. Discussion The definition of thermodynamically significant transplant renal arterial stenosis (TRAS) has not been standardized6; but it is considered significant if more than 60%.7,8 The gold standard for
S. Gandhi et al. / Clinical Queries: Nephrology 5 (2016) 37–39
diagnosis of transplant renal artery stenosis is angiography. Duplex-Doppler examination, performed by an experienced operator, is an invaluable tool for the diagnosis of TRAS. End to end anastomosis have threefold higher risk of developing stenosis than end to side anastomosis3,4; our study includes only patients with end to side anastomosis and these could be the reason for small sample size. In our study 15 patients of TRAS were presented to institute within first 6 months of renal transplantation while only two patients had delayed presentation between 15th and 20th months of post-transplantation. Therefore, Doppler study of 25 patients with good transplantation course (control group) was done at 3 months of post-transplant period. We excluded first 10 post-transplant days to avoid factors like postoperative edema. Controversy exists regarding the optimal PSV cut-off value for suspecting a significant TRAS. Transplant arteries are typically much more tortuous than native renal arteries. This makes the setting of accurate angle correction on spectral Doppler more difficult. The measurement of renal artery PSV played an important role as it is also applied to calculate velocity ratio parameters. We obtained correct angle of insonation that in all instance below 60 degree. Sample gate is placed at most stenotic site and greatest PSV was recorded. Several investigators have demonstrated that using PSV values of 1.8–2.0 m/s as a criterion for the presence of a significant renal artery stenosis, sensitivities of 88–98% and specificities of 62–98% have been achieved.9–11 Baxter et al. used a peak systolic velocity of 2.5 m/s in the transplant renal artery which showed a sensitivity of 100% and a specificity of 95% for detection of renal artery stenosis.12 We found 12.9% higher specificity when we increase threshold of PSV from 2.5 m/s to 3.1 m/s. Our findings are in accordance with Patel et al. which also state that absolute renal artery velocity 2.5 m/s is a limited surrogate marker for significant renal artery stenosis and 3.0 m/s is a better choice.13 We found post-PSV ratio is potential best velocity parameter for diagnosis of significant stenosis. Pre-PSV and post-PSV ratio reflects hemodynamic changes in blood flow velocity and can reduce or eliminate inter individual variations in measurement of renal artery PSV. De Morais et al. found pre-PSV ratio > 1.8 is one of the most accurate parameters in diagnosing TRAS.14 We found threshold of >2.0 for the same. PSV in iliac artery can be affected by aortoiliac or lower extremity vascular disease; while renal artery PSV increases and interlobar artery PSV decreases with the increasingly severity of stenosis.15 This implies that the postPSV ratio is better than pre-PSV ratio for diagnosis of significant RAS. Li et al. found threshold of 5 to diagnosis of more than 50% stenosis in native kidney.15 Li et al. found threshold of 13 for diagnosis of severe (80–90%) stenosis in transplant kidney.16 Their study included 16 patients of TRAS confirmed by DSA; 14 of them had end to end arterial anastomosis. No such cut off point is described in literature to our knowledge for diagnosis of significant (>60%) stenosis in transplant kidney in patients with end to side arterial anastomosis. We found post-PSV ratio is better than other parameters and its optimum threshold 10 for diagnosis of >60% stenosis. Saarinen et al. have shown that a low RI (<0.6) is highly suggestive of TRAS.17 One study showed the sensitivity of intrarenal RI in detecting TRAS was about 85% at cut off point of 0.55.18 We found threshold of <0.58 for the same. Acceleration time greater than 0.07 is used to define stenosis. We found acceleration time useful parameter for diagnosis of significant
39
stenosis but it is a poor predictor to diagnose non-significant stenosis, in accordance with Baxter et al. who also found acceleration time less useful as a discriminating diagnostic test to diagnose renal artery stenosis.12 Limitation of study was we did CT angiography of patients in whom Doppler findings of renal artery stenosis are present. We could not exclude the rare possibility of TRAS in the control group of patients with good transplantation course, normal serum creatinine and blood pressure. 5. Conclusion Post-PSV ratio is the most useful parameter for diagnosis of significant stenosis and to differentiating between significant and non-significant stenosis. Its optimum threshold value is 10. Acceleration time is found to be poor predictor to diagnose nonsignificant stenosis. PSV in main renal artery, pre-PSV ratio and intrarenal RI could not predict degree of stenosis. Conflicts of interest The authors have none to declare. Acknowledgment We are also thankful to our librarian Jyotsana Suthar for literature search and submission. References 1. Faenza A, Spolaore G. Renal artery stenosis after renal transplantation. Kidney Suppl. 1983;14:S54–S59. 2. Tublin ME, Dodd GD. Sonography of renal transplantation. Radiol Clin North Am. 1995;33:447–459. 3. Akbar SA, Jafri SZ, Amen Faenza A, et al. Renal artery stenosis after renal transplantation. Kidney Int Suppl. 1983;14:S54–S59. 4. Jordan ML, Cook GT, Cardella CJ. Ten years of experience with vascular complications in renal transplantation. J Urol. 1982;128:689–692. 5. O’neill DA. Ultrasonography in renal transplantation. Am J Kidney Dis. 2002; 39:663–678. 6. Patel NH, Jindal RM, Wilkin T, et al. Renal arterial stenosis in renal allografts: retrospective study of predisposing factors and outcome after percutaneous transluminalangioplasty. Radiology. 2001;219:663–667. 7. Grossman RA, Dafoe DC, Shoenfeld RB, et al. Percutaneous transluminal angioplasty treatment of renal transplant artery stenosis. Transplantation. 1982;34:339–343. 8. Lacombe M. Arterial stenosis complicating renal allotransplantation in man, a study of 38 cases. Ann Surg. 1975;181:328–330. 9. Olin JW, Piedmonte MR, Young JR, DeAnna S, Grubb M, Childs MB. The utility of duplex ultrasound scanning of the renal arteries for diagnosing significant renal artery stenosis. Ann Intern Med. 1995;122:833–838. 10. Strandness DE. Duplex imaging for the detection of renal artery stenosis. Am J Kidney Dis. 1994;24:674–678. 11. Hansen KJ, Tribble RW, Reavis SW, et al. Renal duplex sonography: evaluation of clinical utility. J Vasc Surg. 1990;12:227–236. 12. Baxter GM, Ireland H, Moss JG, et al. Colour Doppler ultrasound in renal transplant artery stenosis: which Doppler index? Clin Radiol. 1995;50:618–622. 13. Patel U, Khaw KK, Hughes NC. Doppler ultrasound for detection of renal transplant artery stenosis-threshold peak systolic velocity needs to be higher in a low-risk or surveillance population. Clin Radiol. 2003;58:772–777. 14. de Morais RH, Muglia VF, Mamere AE, et al. Duplex Doppler sonography of transplant renal artery stenosis. J Ultrasound. 2003;31:135–141. 15. Li J, Wang L, Jiang Y-x, et al. Evaluation of renal artery stenosis with velocity parameter of Doppler sonography. J Ultrasound Med. 2006;25:735–742. 16. Li JC, Ji ZG, Cai S, Jiang YX, Dai Q, Zhang JX. Evaluation of severe transplant renal artery stenosis with Doppler sonography. J Clin Ultrasound. 2005;33:261–269. 17. Saarinen O, Salmela K, Edgren J. Doppler ultrasound in the diagnosis of renal transplant artery stenosis-value of resistive index. Acta Radiol. 1994;35:586–589. 18. Ardalan MR, Tarzamani MK, Shoja MM. A correlation between direct and indirect Doppler ultrasonographic measures in transplant renal artery stenosis. Transplant Proc. 2007;39:1436–1438.