Imaging Pearls ❯ Vascular ❯ AV fistulae
|
-- OR -- |
|
- Introduction: Role of Imaging
- Conventional angiography and duplex ultrasonography have established roles in delineating access anatomy and complications.
- MDCT is being used more frequently to evaluate peripheral vasculature.
- However, literature on modern 64-MDCT imaging of hemodialysis access is limited (most published studies have employed 4- or 16-MDCT). - AV Fistula – Most Common Configurations
1st choice: Radial artery to cephalic vein at the wrist
- Alternative: Posterior carpal radial artery to cephalic vein (“snuffbox” AV fistula).
2nd choice: Brachial artery to cephalic vein at the elbow.
Upper arm: Brachial artery to transposed basilic vein or axillary vein. - AV Graft – Most Common Configurations
Two primary options in the forearm are:
- Straight graft connecting radial artery to cephalic vein.
- Looped graft between brachial artery and cephalic vein.
Upper arm: Graft connecting brachial artery to axillary vein. - Lower Extremity and Body Wall Accesses
Lower extremity options:
- Femoral artery to femoral vein.
- Superficial femoral artery (SFA) to great saphenous vein (GSV).
- Posterior tibial artery to distal GSV.
Body wall options (uncommon):
- Straight graft between axillary artery and contralateral axillary vein (“necklace” graft).
- Looped graft between axillary artery and ipsilateral axillary vein.
- Looped graft between axillary artery and ipsilateral jugular vein. - MDCT Angiography (MDCTA) with 3-D Reconstruction
- High spatial and temporal resolution.
- 3-D angiography with maximum-intensity projection (MIP) and volume rendering (VR) improves detection of complications.
- Allows detection of extra-vascular and central venous pathology.
- Results are often comparable to digital subtraction angiography (DSA).
- VR is particularly useful for detecting aneurysms, including partially thrombosed aneurysms missed on DSA.
- Stenosis/occlusion >50% can be detected with accuracy, sensitivity, and specificity of 92%, 90%, and 93%, respectively.
False-negatives seen in cases of stenosis adjacent to nitinol stent.
False-positives from vein compression secondary to arm positioning.
- Disadvantage: Exposure to radiation - Hemodialysis access Complications
- Venous and arterial stenosis/thrombosis
- Accessory veins
- Arterial steal syndrome
- Aneurysms and pseudoaneurysms
- AV graft stenosis and thrombosis
- Infection
- Hematomas, seromas, and lymphoceles - Venous Stenosis
- Most common cause of both early and late fistula failure.
- Locations of venous stenosis:
- Juxta-anastamosis (JAS): within 5 cm of anastamosis.
- Proximal vein: between anastamosis and central veins.
- Central venous: subclavian vein, brachiocephalic vein, and SVC.
- Intervention prior to the formation of thrombus is critical for prolonged access survival.
- Percutanous balloon-assisted angioplasty (PTA) of peripheral stenotic vessels is the treatment of choice with greater than 90% salvage rate.
- Central venous stenosis:
- Patients with prior history of central venous catherization are prone to developing central venous stenosis and/or thrombosis, with rates as high as 40%.
- Vascular stents are typically used to restore patency, but surgical bypass may also be performed. - Venous Thrombosis
- Prolonged stenosis can result in thrombosis.
- Management:
- Endovascular treatment methods include thrombolysis and/or mechanical lysis.
- Surgical thrombectomy with revision.
- Both are considered effective therapies. - Arterial Stenosis/Thombosis and Arterial Steal Syndrome
- The risk of arterial stenosis increases with time, reported to be as high as 15-30%.
- Arterial intervention, typically PTA, is undertaken in cases of greater than 50% stenosis with associated functional or hemodynamic abnormalities.
- Arterial stenosis can also predispose to steal syndrome, which is most commonly observed in radiocephalic fistulae.
- Problems of arterial inflow due to thrombosis are not uncommon and require angiographic evaluation. Endovascular methods, such as pharmacologic thrombolysis or mechanical lysis, are favored over surgical thrombectomy in the management of AVF thrombosis. - Aneurysm and Pseudoaneurysm
- Aneurysmal dilatation is defined as greater than 150% the normal diameter of a vessel.
- True aneurysms may form secondary to increased venous pressure proximal to a more central stenosis or immunosuppression.
- Pseudoaneurysms can result from repeated punctures in the same area or from deterioration of graft material over an extended period of time.
- Aneurysms and pseudoaneurysms are at increased risk of rupture and infection, and may also cause erosion of overlying skin.
- An AV graft pseudoaneurysm that measures greater than twice the diameter of the graft (usually >4 cm) requires surgical or endovascular intervention. - AV Graft Stenosis and Thrombosis
- AV grafts have lower primary and secondary patency rates in comparison to AVF.
- Complications of AV grafts are well demonstrated on MDCT angiography.
- Stenosis with resulting thrombosis is most commonly noted at the venous anastamotic site of an AV graft, likely secondary to intimal hyperplasia.
- Venous anastamotic stenosis is typically treated with percutaneous balloon angioplasty with or without stenting. Surgical patch angioplasty and bypass grafts are less common.
- Endovascular methods and surgical thrombectomy with revision are both considered effective therapies for AV graft thrombosis.
- “Primary arteriovenous fistulae remain the gold standard for hemodialysis access. The radiocephalic or Brescia-Cimino fistula is the autologous fistula of choice, with a primary success rate of nearly 93% and a 1-year patency rate of up to 82%. Alternative arteriovenous fistulae include the snuff box fistula and a brachiobasilic fistula with a 1-year patency rate of up to 90%. Complications include thrombosis, infection, arterial steal syndrome, venous hypertension, aneurysms, and congestive heart failure. Despite these complications, arteriovenous fistulae provide good long-term hemodialysis access.”
Arteriovenous fistulae for hemodialysis.
Burkhart H et al
Semin Vasc Surg 1997 Sep;10(3):162-5 - “Placement of permanent vascular access: selection of appropriate access type, pre-operative examination of the vessels, preparation and placement of vascular access, and nursing care of the arteriovenous fistula and graft. Patients with chronic kidney disease need to consider which treatment modality they will have once their disease has progressed to end-stage kidney disease requiring renal replacement therapy. For patients who consider haemodialysis as an option, the decision needs to be made in a timely manner so that adequate vascular access is achieved before starting dialysis.”
KHA-CARI guideline: Vascular access - central venous catheters, arteriovenous fistulae and arteriovenous grafts.
Polkinghorne KR et al
Nephrology (Carlton). 2013 Jul 16. doi: 10.1111/nep.12132. [Epub ahead of print]