AV fistula aneurysm: how to cannulate it and when to refer
Aneurysms are a common complication of the hemodialysis arteriovenous fistula. Most are stable, but some can rupture and bleed massively. This guide explains how to tell a true aneurysm from a pseudoaneurysm, what to look for on ultrasound, how to cannulate an aneurysmal fistula and which warning signs call for urgent referral.
Key points
- A true aneurysm keeps all layers of the vessel wall. A pseudoaneurysm is a hematoma that communicates with the lumen, with a wall made of fibrous tissue [2,6].
- There is no universal definition. A diameter over 18 mm, or three times the maturation diameter, has been proposed [4,5], and reported incidence ranges from 5% to 60% depending on the criteria used [2].
- Don't cannulate the dome, thin skin or scabs. Use the healthy segments beside the aneurysm and rotate sites with the rope ladder technique [1,2].
- Thin, shiny skin, ulceration, a scab, bleeding, rapid growth, pain or infection need urgent assessment. Rupture is a life-threatening emergency [2,3].
- Size alone is not an indication for treatment: skin condition, symptoms, ease of cannulation and access flow decide [5].
AV fistula aneurysm vs pseudoaneurysm
After a fistula is created, the vein dilates, often irregularly: that is expected and makes cannulation easier. This is why it's hard to say when a dilatation becomes an aneurysm [2,3]. Published definitions use an absolute diameter (over 20–30 mm), a 2- to 3-fold increase over the adjacent segment, or the sum of the diameters [2]. An expert consensus proposed 18 mm, or three times the accepted maturation diameter [4].
| True aneurysm | Pseudoaneurysm (false aneurysm) | |
|---|---|---|
| Wall | All layers of the vessel wall, dilated | No vessel wall: fibrous tissue and organized hematoma around a cavity with flow |
| Origin | Repeated cannulation of the same area, high flow, stenosis, a predisposed vessel wall | Blood leaking through a traumatic needle hole or the anastomosis |
| Course | Usually stable for years | Can grow quickly |
| Ultrasound | Fusiform or saccular dilatation, slow swirling flow, sometimes mural thrombus | A collection with a neck connecting it to the vessel; "yin-yang" sign on color Doppler |
Table sources: GEMAV [2], Mudoni et al. [3] and Sharbidre et al. [6].
What causes an aneurysm in a fistula?
- Repeated cannulation of the same segment (area puncture). It weakens the wall and predisposes it to dilate, a pattern known as "one-site-itis" [2]. Needle scars expand over time and form localized dilatations [3].
- High flow. Shear stress promotes outward remodeling and gradual dilatation, even in segments that are never cannulated [3].
- Outflow stenosis. A stenosis further along the vein raises the pressure in the segment upstream of it [2,3].
- A predisposed vessel wall, for example in polycystic kidney disease or Alport syndrome [2,3].
- Pseudoaneurysm: traumatic cannulation, prolonged bleeding after needle removal or a leaking anastomosis. In grafts, repeated cannulation of the same area [2,3].
What it looks like on ultrasound
Diagnosis is mainly clinical. Doppler ultrasound measures the aneurysm and shows whether it contains thrombus [2]. A complete scan includes [3,6]:
- Maximum diameter in transverse and long axis, and the length of the dilated segment.
- Thickness of the tissue covering the dome (skin and wall). If it is very thin, that area must not be cannulated.
- Mural thrombus: echogenic material attached to the wall, seen as a filling defect on color Doppler.
- Flow: blood moves more slowly inside an aneurysm and may swirl. The classic "yin-yang" sign (to-and-fro red and blue flow with a neck) is typical of a pseudoaneurysm [6].
- Stenosis before or after the aneurysm: look for color aliasing and a raised velocity ratio. If present, it should be treated [3].
- A hematoma has no flow inside it; a pseudoaneurysm does [6].
How to cannulate an aneurysmal fistula
- Don't cannulate the dome or areas with altered skin, scabs, signs of infection or hematoma. GEMAV specifically says to avoid the apex of aneurysms [2].
- Use the adjacent segments of normal diameter, with enough wall and tissue thickness. Map them with ultrasound first [3].
- Don't go through mural thrombus. If thrombus lines the deep wall, the needle tip can end up inside it instead of in the lumen.
- Rotate sites with the rope ladder technique. KDOQI considers it the best-practice method and does not recommend area puncture [1]. GEMAV recommends the rope ladder as the preferred method for native fistulas [2].
- Buttonhole is an option for selected cases. KDOQI reserves it for special circumstances, including enlarging aneurysms [1]. GEMAV limits it to tortuous or deep fistulas, or those with a very short usable segment [2].
- Hold good pressure at needle removal without occluding flow: prolonged bleeding after cannulation favors hematomas and pseudoaneurysms [2,3].
- In grafts, don't cannulate a small pseudoaneurysm: monitor it with Doppler instead [2].
Warning signs: when to refer urgently
Most aneurysms are benign and stable. Thick-walled aneurysms covered by healthy skin carry a low risk of rupture [3]. Risk rises when the skin changes or the aneurysm grows. Bleeding is the main complication of venous aneurysms: it can be massive and life-threatening [2].
Signs that need same-day assessment by the nephrologist or vascular surgeon: thin, shiny or depigmented skin over the aneurysm; an ulcer, erosion or scab that doesn't heal; bleeding through the skin or prolonged bleeding after needle removal; rapid growth; pain; redness, warmth or discharge. With ulceration, a scab or infection, rupture may be imminent and urgent treatment is indicated [2,3,6]. If the aneurysm bleeds: apply firm, direct pressure over the bleeding point and call emergency services (911). Don't cannulate it until a specialist has assessed it.
Teach these signs to patients too. In a review of 88 deaths from vascular access hemorrhage, 78% of those with a known location happened at home or in a nursing home, outside a healthcare setting [7].
AV fistula aneurysm treatment options
Treatment is not based on trials but on case series and each center's experience [2,4]. The decision always belongs to the vascular access team. In general terms:
- Surveillance: many stable aneurysms only need baseline measurements and clinical and ultrasound follow-up [3,4].
- Indications for treatment: skin changes (atrophy, erosions, inflammation, scabs), thrombosis, venous hypertension, high flow or cosmetic reasons. GEMAV suggests surgery for venous aneurysms with significant stenosis, necrosis or skin changes with a risk of rupture [2]. Rupture is an emergency requiring urgent surgery [2].
- Surgery: aneurysmorrhaphy, partial resection, resection with direct end-to-end repair or graft interposition. The goal is to preserve the access [2,3].
- Endovascular: a covered stent excludes the aneurysm and can treat a stenosis at the same time, but it makes cannulating the treated segment difficult [2,4].
- Needle-site pseudoaneurysm in a native fistula: first, ultrasound-guided manual compression; if that fails, ultrasound-guided thrombin injection; and surgery if both fail [2].
Prevention
- Rope ladder cannulation along the whole usable length of the vein, never always in the same spot [1,2].
- An access map in the patient's record, with the anatomy and flow direction, to plan sites [2].
- Ultrasound-guided site rotation when the vein is short or irregular, to pick segments with a healthy wall.
- Surveillance: examine the aneurysm before every treatment and measure it with ultrasound if it changes. Look for and treat stenosis [3].
Frequently asked questions
What is the difference between an AV fistula aneurysm and a pseudoaneurysm?
A true aneurysm is a dilatation of the vessel itself, with all layers of its wall. A pseudoaneurysm is a pulsatile hematoma connected to the lumen through a hole, with a wall of fibrous tissue. It usually follows traumatic cannulation and can grow quickly [2,6].
Can you cannulate an aneurysmal fistula?
Yes, but not over the dome or over thin or scabbed skin. Cannulate the normal-diameter segments beside it, check with ultrasound that the wall and tissue are thick enough, and rotate sites using the rope ladder technique [1,2,3].
What causes an aneurysm in a fistula?
Repeated cannulation of the same area, high flow, an outflow stenosis or a predisposed vessel wall. Pseudoaneurysms are caused by traumatic cannulation or poor hemostasis [2,3].
When is an AV fistula aneurysm dangerous?
When the overlying skin becomes thin and shiny, or an ulcer or scab appears, or it bleeds, grows quickly, hurts or becomes infected. These signs point to a risk of rupture and need urgent assessment [2,3]. If it bleeds, apply direct pressure and call emergency services.
How is an AV fistula aneurysm treated?
Many are simply monitored. With skin changes, thrombosis or stenosis, the vascular access team may recommend surgery (aneurysmorrhaphy, resection or a graft) or, in selected cases, a covered stent. The aim is always to preserve the access [2,3,4].
Educational content. It does not replace supervised hands-on training or your unit's protocols.
References
- Lok CE, Huber TS, Lee T, et al. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update (guideline 11, cannulation methods). Am J Kidney Dis. 2020;75(4 Suppl 2):S1–S164. doi.org
- Ibeas J, Roca-Tey R, Vallespín J, et al. Spanish Clinical Guidelines on Vascular Access for Haemodialysis (GEMAV), sections 3.3 (use of the AVF) and 5.6 (aneurysms and pseudoaneurysms). Nefrología. 2017;37(Suppl 1):1–191. doi.org
- Mudoni A, Cornacchiari M, Gallieni M, et al. Aneurysms and pseudoaneurysms in dialysis access. Clin Kidney J. 2015;8(4):363–367. doi.org
- Inston N, Mistry H, Gilbert J, et al. Aneurysms in vascular access: state of the art and future developments. J Vasc Access. 2017;18(6):464–472. doi.org
- Balaz P, Björck M. True aneurysm in autologous hemodialysis fistulae: definitions, classification and indications for treatment. J Vasc Access. 2015;16(6):446–453. doi.org
- Sharbidre KG, Alexander LF, Varma RK, et al. Hemodialysis access: US for preprocedural mapping and evaluation of maturity and access dysfunction. RadioGraphics. 2024;44(1):e230053. doi.org
- Ellingson KD, Palekar RS, Lucero CA, et al. Vascular access hemorrhages contribute to deaths among hemodialysis patients. Kidney Int. 2012;82(6):686–692. doi.org