Hemodialysis access imaging: comparison of flow-interrupted contrast-enhanced MR angiography and digital subtraction angiography

Magnetic Resonance Techniques in Hemodialysis access Management

In this review we describe current applications and future perspectives of MR angiography, MR flow quantification, and interventional MRI in hemodialysis access management. Each section starts with a brief overview of the main techniques that are currently available or under development. This is followed by a survey of the pertinent literature. Each section concludes with a discussion of the reported findings and an indication of research opportunities.

Magnetic Resonance Angiography of the Upper Extremity

The magnetic resonance angiography (MRA) toolbox includes a wide array of versatile methods for diagnosis and therapy planning in patients with a variety of upper extremity vascular pathologies. MRA can provide excellent image quality with high spatial and high temporal resolution without the disadvantages of ionizing radiation, iodinated contrast, and operator dependency. Contrast-enhanced techniques are preferred for their robustness, image quality, and shorter scan times. This article provides an overview of the available MRA techniques and a description of the clinical entities that are well suited for evaluation with contrast-enhanced MRA.

Vascular Access Monitoring and Surveillance: An Update

Vascular access in dialysis patients remains both a critical link to survival and a significant source of morbidity. Currently, the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) vascular access guidelines recommend routine vascular access monitoring and encourage dedicated surveillance techniques to be used for early detection of access stenosis and prevention of thrombosis. There is a paucity of clear evidence supporting 1 surveillance technique over another. The purpose of this review is to describe the benefits and limitations of various surveillance techniques commonly used in the care of dialysis patients. Further studies in this area will be useful to determine the most appropriate combination of aggressive clinical monitoring and additional surveillance data to strike a balance between graft thrombosis and unnecessary vascular interventions.

Series of Noncontrast Time-of-Flight Magnetic Resonance Angiographies to Identify Problems with Arteriovenous Fistula Maturation

BACKGROUND

Successful maturation of arteriovenous fistulas (AVFs) remains a challenge for those managing patients with end-stage renal disease. Time-of-flight magnetic resonance angiography (TOF-MR) can be used to evaluate AVFs without the risk of radiation exposure, intravenous contrast, or reliance on the operator-dependent modality of color Doppler ultrasonography (CDUS). The objective of our study was to assess the utility of TOF-MR in the evaluation of nonmaturing AVFs and to identify the best clinical situations to use this technology.

METHODS

Consecutive patients with abnormal findings on CDUS or physical examination after AVF creation underwent 3-dimensional (3D) TOF-MR. Imaging was performed at 3 T with a scan acquisition time of approximately 15 min. The technique was similar to head and neck magnetic resonance angiography (MRA), except presaturation bands were not used, thereby allowing simultaneous visualization of both arterial and venous flow. A total of 19 TOF-MR studies were performed.

RESULTS

Nineteen patients underwent imaging and were the focus of this study. Seventeen of 19 TOF-MR studies were of diagnostic quality and yielded findings which enabled the vascular surgeon to take corrective measures. Findings included inflow stenosis, anastomotic narrowing, venous outflow stenosis, and hemodynamically significant venous tributaries. Twelve of 17 patients required conventional digital subtraction angiography (DSA). The congruence rate between TOF-MR and DSA was 83.3%. Four patients (21%) avoided DSA and went directly to definitive surgical treatment including branch ligation (3) or new access (1).

CONCLUSIONS

This is the first report in the literature of successful implementation of 3D TOF-MR to assist in identifying AVF maturation problems. This unique noninvasive imaging modality provides actionable images without contrast or radiation exposure and can obviate the need for invasive diagnostic procedures or provide an anatomic map for planning corrective intervention.

Review of Transposed Basilic Vein Access for Hemodialysis

Background

There is ongoing debate about the use of transposed basilic vein (TBV) fistula and the choice between it and prosthetic arteriovenous graft (AVG). This paper reviews the available literature relating to TBV fistula in terms of surgical technique, patency rates, complications, access survival and compares it with prosthetic AVG for hemodialysis (HD).

Methods

Review of English language publications on TBV during the last two decades.

Findings

The rate of fistula maturation was higher in the two-stage group, although the mean diameter of the basilic vein was smaller. Dialysis via central venous catheters at time of surgery was most prevalent in patients undergoing staged procedures—14% in one-stage TBV and 43% in two-stage TBV. Several authors report 1-year cumulative patency rate of 47% to 96% and 59% to 90% for TBV and AVG, respectively. TBV provides a more cost-effective option and should be considered the next choice when primary autogenous fistulae are not possible, whereas AVGs are easier to create, can be punctured earlier and have a greater reintervention rate if the access fails.

Conclusions

This analysis shows that TBV has several advantages over AVG and provides a valuable access for HD but raises the need for a comparative trial between TBV and the newer generation AVGs. There is no clear superiority of the one-stage over the two-stage procedure.

Embolic occlusion of arteriovenous fistula due to infective endocarditis

A 45-year-old male on maintenance hemodialysis through right radio cephalic arteriovenous fistula (AVF) also had mitral regurgitation. He presented with fever and chills of 2 days duration along with pain and swelling at median cubital fossa of right upper limb. Local examination revealed warmth, redness, and tenderness at median cubital fossa. AVF thrill was absent. Echocardiography revealed vegetations on the mitral valve. An extensive search of literature did not reveal an instance of embolic occlusion of AVF due to vegetations of infective endocarditis.

64-slice MDCT angiography of upper extremity in assessment of native hemodialysis access

OBJECTIVE

To compare multidetector row computed tomographic (MDCT) angiography with conventional digital subtraction angiography (DSA) in the evaluation of vascular access stenoses in hemodialysis patients.

MATERIALS AND METHODS

Twenty-one consecutive patients were imaged with MDCT angiography and subsequent DSA. The superficial vein of leg was used as the route for intravenous administration. The vascular stenosis was assessed in not significant (<50% stenosis), moderate stenosis (50%-74% stenosis), severe stenosis (75%-99%), and total occlusion (100%). The accuracy, sensitivity, specificity, positive, and negative predictive values were calculated for significant vascular stenosis using DSA as the standard reference.

RESULTS

The sensitivity and specificity of MDCT angiography for the detection of significant hemodialysis vascular access were 100% (95% CI, 89.3%-100%) and 94.8% (95% CI, 89.1%-97.6%), respectively. The positive and negative predictive values were 84.2% (95% CI, 68.1%-93.4%) and 100% (95% CI, 95.8%-100%), respectively. The accuracy of MDCT angiography for detection of significant stenoses was 95.9% (95% CI, 91.4%-97.0%).

CONCLUSIONS

MDCT angiography provides excellent correlation in vascular stenosis as compared with DSA in hemodialysis access. Complete assessment of entire vascular segments could be performing with MDCT angiography in planning before endovascular intervention or surgical correction.

Current concepts in the pathophysiology and management of arteriovenous access-induced hand ischemia

The manifestations of hand ischemia because of an arteriovenous access can range from hand pain, tissue necrosis, and loss of the entire hand. Recent data have emphasized that multiple mechanisms (arterial steal, ie, retrograde flow, arterial stenosis, and arterial calcification) are responsible for inducing hand ischemia. Because any or a combination of the 3 mechanisms can lead to peripheral ischemia, distal hypoperfusion ischemic syndrome is a more appropriate term to denote hand ischemia. A detailed history, physical examination, and differential diagnosis form the initial step in the management of distal hypoperfusion ischemic syndrome. A complete arteriogram to evaluate the circulation of the extremity from the aortic arch to the palmar arch is essential. The choice of treatment modality should be based on this evaluation. In this article, we review the pathophysiology and present current strategies to ameliorate distal hypoperfusion ischemic syndrome.

Longitudinal assessment of hyperplasia using magnetic resonance imaging without contrast in a porcine arteriovenous graft model

RATIONALE AND OBJECTIVES

Chronic hemodialysis requires a vascular access that provides high blood-flow rates for the extracorporeal recirculation of blood. Synthetic arteriovenous (AV) grafts often fail because of clotting caused by underlying hyperplasia formation. The authors report the use of magnetic resonance (MR) imaging (MRI) without contrast agent to monitor tissue hyperplasia formation as well as luminal area in a porcine model of AV graft stenosis.

MATERIALS AND METHODS

Expanded reinforced polytetrafluoroethylene grafts were surgically placed between the common carotid artery and the external jugular vein, bilaterally, in pigs. Animals underwent MRI in a 3-T scanner at 3, 4, or 6 weeks after graft placement, followed by euthanasia and the collection of grafts and adjacent tissues for histologic analysis. Two animals underwent sequential scanning at 1, 2, 3, 5, and 7 weeks after graft placement, followed by histologic analysis.

RESULTS

Measurements of hyperplasia obtained from the MR images were compared with, and correlated well with, measurements obtained from the histologic cross-sections (r = 0.932, P = .02). The MR images provided a more complete view of the venous hyperplasia throughout the graft compared with histology. The MR images could be examined from multiple angles and were unaffected by histologic preparation artifacts.

CONCLUSION

Unlike histology, MRI provided longitudinal 3-dimensional views of hyperplasia within the AV grafts. This ability of MRI to more completely identify the geometry of hyperplasia and to quantify the tissue volume in vivo could provide benefits over histologic analysis in assessing the pathology of AV graft failure and the efficacy of antihyperplasia interventions.

Dynamic MR angiography of upper extremity vascular disease: pictorial review

Unlike peripheral lower extremity vascular disease, upper extremity vascular disease is relatively uncommon. While atherosclerosis and embolic disease are the most common causes of upper extremity ischemia, a wide variety of systemic diseases and anatomic abnormalities can affect the upper extremity. Upper extremity ischemia poses a significant diagnostic and therapeutic challenge for both clinicians and radiologists. Although history and physical examination remain the mainstays of diagnosis, imaging can be vital in confirming suspected disease and guiding treatment planning. Digital subtraction angiography is often the preferred method for detection of upper extremity vascular disease, particularly for characterization of complex arteriovenous anatomy such as in vascular malformations and for evaluation of dialysis fistulas and grafts. However, this modality is invasive, requires iodinated contrast agents and radiation, and may fail to demonstrate significant extraluminal disease. More recently, magnetic resonance (MR) angiography techniques have made important advances, permitting higher temporal and spatial resolution that is preferable for diagnosing upper extremity vascular disorders. In this review, the authors present an overview of upper extremity MR angiography techniques and protocols, revisit the often variable vascular anatomy of the arm and hand, and offer examples of various pathologic entities diagnosed with MR angiography. Finally, several imaging pitfalls that one must be aware of for accurate diagnosis are illustrated and reviewed.

Time-resolved, high-resolution contrast-enhanced MR angiography of dialysis shunts using the CENTRA keyhole technique with parallel imaging

PURPOSE

To evaluate the use of a dynamic keyhole magnetic resonance angiography (MRA) sequence combined with sensitivity encoding (SENSE) for hemodialysis shunts, because surveillance with conventional contrast-enhanced MRA (CE-MRA) is limited by its low temporal resolution, resulting in arteriovenous overlay.

MATERIALS AND METHODS

A total of 12 patients with Brescia-Cimino shunts were investigated prospectively using the new technique. During the contrast passage (gadoterate, Gd-DOTA) a series of five to nine dynamic central k-space measurements (10% for upper-arm shunt, 25% for lower-arm shunt) followed by a full reference data set were acquired. The outer k-space data of the single reference scan were used to complete the dynamic data sets.

RESULTS

All studies were diagnostic (17 stenoses, three aneurysms) without complications. The acquisition times for a single dynamic scan of the upper- and lower-arm shunts were 2.2 and 3.2 seconds, respectively, while the reference scan needed 13 and 22.4 seconds, respectively. The dynamic angiograms allowed the differentiation of arterial and venous filling despite a mean peak delay time of only 4.2 seconds in the shoulder region. Image quality qualified in consensus by two experienced readers was rated "good" in 19 cases and "intermediate" in five cases with high mean values for signal-to-noise ratios (SNRs) and contrast-to-noise-ratios (CNRs).

CONCLUSION

We have successfully implemented a fast, dynamic, CE-MRA technique with CE timing robust angiography (CENTRA) keyhole and SENSE in clinical routine. High spatial and temporal resolution improve the diagnostics of dialysis shunts and allow the assessment of detailed, dynamic, four-dimensional (4D) information.

Arteriovenous access and hand pain: the distal hypoperfusion ischemic syndrome

An ischemic hand in a hemodialysis patient is a serious condition. It causes significant pain and discomfort but also can lead to tissue necrosis and the eventual loss of digits and even the entire hand. Although stealing of blood away from the high-resistance forearm arteries into the low-resistance arteriovenous access generally is assumed to be the cause, a great majority of both wrist and elbow accesses demonstrate retrograde flow without any evidence of hand pain or ischemia. Consequently, demonstration of retrograde flow alone does not predict or indicate the existence of distal ischemia. In this context, the term "arterial steal syndrome" is a misnomer to indicate the presence of peripheral ischemia. Recent studies have shown that, in many cases, arterial stenotic lesions cause distal hypoperfusion and result in hand ischemia. In other cases, distal arteriopathy as a result of generalized vascular calcification and diabetes is the culprit. Because any or a combination of the three mechanisms (retrograde flow, stenotic lesions, and distal arteriopathy) can lead to peripheral ischemia, distal hypoperfusion ischemic syndrome is a more appropriate term to denote hand ischemia. Treatment should start with a detailed history and physical examination to help rule out other (nonischemic) causes of hand pain. A complete arteriogram to evaluate the circulation of the extremity from the aortic arch to the palmar arch is essential. The choice of treatment modality and procedure to apply should be based on this evaluation. This report reviews the pathophysiology and presents current strategies to ameliorate distal hypoperfusion ischemic syndrome.

Inflow stenoses in dysfunctional hemodialysis access fistulae and grafts

BACKGROUND

The aim of the study is to prospectively determine the incidence of inflow stenoses in dysfunctional hemodialysis access arteriovenous fistulae (AVFs) and grafts (AVGs).

METHODS

Contrast-enhanced magnetic resonance angiography (CE-MRA) was performed of 66 dysfunctional AVFs and 35 AVGs in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years). Complete inflow (from the subclavian artery), shunt region, and complete outflow (including subclavian vein) were shown at CE-MRA. In addition to standard digital subtraction angiography (DSA) of the shunt region and outflow, DSA of the complete inflow was obtained through access catheterization of all cases in which CE-MRA showed an inflow stenosis. Vascular stenosis is defined as greater than 50% decrease in luminal diameter compared with an uninvolved vascular segment located adjacent to the stenosis. Endovascular intervention of stenoses was performed in connection with DSA.

RESULTS

CE-MRA showed 19 arterial stenoses in 14 patients (14%). DSA confirmed 18 of these lesions in 13 patients and showed no additional inflow lesions. Of the 13 patients, 7 patients had arterial stenoses only and 6 patients had accompanying stenoses in the shunt region and/or outflow. Referral criteria for the 13 patients to undergo access evaluation had been decreased flow rates (9 patients), steal symptoms (2 patients), and insufficient access maturation (2 patients). Access flow of the 9 patients with a low-flow access improved from 477 +/- 74 mL/min to 825 +/- 199 mL/min after angioplasty. One patient with steal symptoms became symptom free after angioplasty. Endovascular intervention in 3 patients proved to be unsuccessful.

CONCLUSION

Inflow stenoses are not uncommon in dysfunctional hemodialysis access shunts. We suggest that radiological evaluation comprise assessment of the complete arterial inflow.

Time-Resolved 3D MR Angiography with Parallel Imaging for Evaluation of Hemodialysis Fistulas and Grafts: Initial Experience

OBJECTIVE

We optimized a time-resolved 3D contrast-enhanced MR angiography sequence with integrated parallel imaging technique that can provide a large field of view with high temporal and spatial resolution, by which the hemodialysis access and the entire course of the inflow and outflow vessels can be imaged at a single anatomic station. Our objective was to evaluate the feasibility and usefulness of this method in the evaluation of patients referred for possible abnormalities in hemodialysis access.

CONCLUSION

Time-resolved contrast-enhanced 3D MR angiography with parallel imaging has the potential to provide a rapid and comprehensive evaluation for the surveillance and diagnosis of hemodialysis access malfunctions. This technique may function as an important complement to conventional digital subtraction angiography and may be able to help guide medical management. The MR angiography protocol we present is a noninvasive, versatile, and time-efficient technique, without the need of direct graft puncture or flow interruption, and can be performed using a single injection of contrast material at a single station.

Access Monitoring Is Worthwhile and Valuable

During the past several years, a limited number of small clinical trials have questioned the role of surveillance in the management of vascular accesses, since the prolongation of access longevity until replacement was not altered. Although prolongation of access life span is an important endpoint, it is not the only one. Reduction in thrombotic events reduces the risks to the patient resulting from loss of access patency. The body of evidence suggests that the detection of stenosis and prevention of thrombosis are valuable. When a test indicates the likely presence of a stenosis, venography or fistulography should be used to definitely establish the presence and the degree of the stenosis. In most cases, angioplasty should be performed if the stenosis is greater than 50% by diameter. The value of routine use of any surveillance technique for detecting anatomic stenosis alone without concomitant functional assessment by measurement of access flow, venous pressure, recirculation, or other physiologic parameter has not been established. Stenotic lesions should not be repaired merely because they are present. If such correction is performed, then intra-procedural studies of access flow or intra-access pressure prior to and following percutaneous transluminal angioplasty should be conducted to demonstrate a functional improvement with a 'successful' percutaneous transluminal angioplasty.

Stenosis detection in failing hemodialysis access fistulas and grafts: comparison of color Doppler ultrasonography, contrast-enhanced magnetic resonance angiography, and digital subtraction angiography

OBJECTIVE

Several imaging modalities are available for the evaluation of dysfunctional hemodialysis shunts. Color Doppler ultrasonography (CDUS) and digital subtraction angiography (DSA) are most widely used for the detection of access stenoses, and contrast-enhanced magnetic resonance angiography (CE-MRA) of shunts has recently been introduced. To date, no study has compared the value of these three modalities for stenosis detection in dysfunctional shunts. We prospectively compared CDUS and CE-MRA with DSA for the detection of significant (> or = 50%) stenoses in failing dialysis accesses, and we determined whether the interventionalist would benefit from CDUS performed before DSA and endovascular intervention.

METHODS

CDUS, CE-MRA, and DSA were performed of 49 dysfunctional hemodialysis arteriovenous fistulas and 32 grafts. The vascular tree of the accesses was divided into three to eight segments depending on the access type (arteriovenous fistula or arteriovenous graft) and the length of venous outflow. CDUS was performed and assessed by a vascular technician, whereas CE-MRA and DSA were interpreted by two magnetic resonance radiologists and two interventional radiologists, respectively. All readers were blinded to information from each other and from other studies. DSA was used as reference standard for stenosis detection.

RESULTS

DSA detected 111 significant (> or = 50%) stenoses in 433 vascular segments. Sensitivity and specificity of CDUS for the detection of significant stenosed vessel segments were 91% (95% CI, 84%-95%) and 97% (95% CI, 94%-98%), respectively. We found a positive predictive value of 91% (95% CI, 84%-95%) and a negative predictive value of 97% (95% CI, 94%-98%). The sensitivity, specificity, positive predictive value, and negative predictive value of MRA were 96% (95% CI, 90%-98%), 98% (95% CI, 96%-99%), 94% (95% CI, 88%-97%), and 98% (95% CI, 96%-99%), respectively. CDUS and CE-MRA depicted respectively three and four significant stenoses in six nondiagnostic DSA segments. The interventionalist would have chosen an alternative cannulation site in 38% of patients if the CDUS results had been available.

CONCLUSIONS

We suggest that CDUS be used as initial imaging modality of dysfunctional shunts, but complete access should be depicted at DSA and angioplasty to detect all significant stenoses eligible for intervention. CE-MRA should be considered only if DSA is inconclusive.

Stenosis detection with MR angiography and digital subtraction angiography in dysfunctional hemodialysis access fistulas and grafts

PURPOSE

To prospectively assess three-dimensional contrast material-enhanced magnetic resonance (MR) angiography for stenosis depiction in malfunctioning hemodialysis arteriovenous fistulas (AVFs) and grafts (AVGs), as compared with digital subtraction angiography (DSA).

MATERIALS AND METHODS

Ethical review board approval and written informed consent were obtained. MR angiography and DSA were performed in 51 dysfunctional hemodialysis fistulas and grafts in 48 consecutive patients. Vascular tree of accesses was divided into between three and eight segments depending on access type (AVF or AVG) and length of venous outflow. Images obtained with MR and DSA were interpreted by two MR radiologists and two interventional radiologists, respectively, who were blinded to information from each other and other studies. DSA was reference standard for stenosis detection. Sensitivity, specificity, and predictive values with 95% confidence intervals (CIs) of contrast-enhanced MR in detection of vascular segments containing hemodynamically significant (> or =50%) stenosis were calculated. Linear-weighted kappa statistic was calculated for contrast-enhanced MR and DSA to determine interobserver agreement regarding stenosis detection.

RESULTS

A total of 282 vascular segments were evaluated. Contrast-enhanced MR depicted three false-positive stenoses and all but two of 70 significant stenoses depicted with DSA. Sensitivity, specificity, and positive and negative predictive values of MR in detection of vessel segments with significant stenoses were 97% (95% CI: 90%, 99%), 99% (95% CI: 96%, 100%), 96% (95% CI: 88%, 99%), and 99% (95% CI: 97%, 100%), respectively. MR demonstrated significant stenosis in four of five nondiagnostic DSA segments, whereas DSA showed no significant stenosis in four nondiagnostic MR segments. Linear-weighted kappa statistic for interobserver agreement regarding stenosis detection was 0.92 (95% CI: 0.89, 0.95) for MR and 0.95 (95% CI: 0.92, 0.97) for DSA.

CONCLUSION

MR angiography depicts stenoses in dysfunctional hemodialysis accesses but has limited clinical value as result of current inability to perform MR-guided access interventions after stenosis detection. MR of dysfunctional access should be considered only if nondiagnostic vascular segment is present at DSA.