European Journal of Cardiovascular Medicine

Aneurysm development varies widely from 6% to 60% of chronic kidney disease patients who receive regular dialysis via arteriovenous access¹. Therefore, aneurysms can be considered as one of the important complications that need prompt management. An arteriovenous fistula is preferable to temporary dialysis access to guarantee long-term and satisfactory hemodialysis treatment.

The Society for Vascular Surgery defines a true aneurysm as a focal dilatation of intimal, medial and adventitial layers of the vessel wall². A pseudoaneurysm on the other hand is defined as a focal dilatation of the vessel wall by neointimal and fibrous tissue². In terms of aneurysm size, current guidelines offer no strict criteria to define and classify arteriovenous fistula aneurysm (AVFA). The suggested diameter of a usable AVF is 6 mm in the K/DOQI guidelines³, which is approximately three times greater than the diameter of a typical autologous vein⁴^,⁵. In the published literature, the reported sizes of AVFA range between 19.5 mm and 80 mm, which encompasses more than threefold expansion of the advocated diameter of an AVF vein.

Valenti et al.⁶ defined AVFA as any segment of a vein with

a diameter greater than 18 mm and Balaz et al.⁷ proposed a definition of AVFA as a dilatation of all three vein layers to at least a diameter of 18 mm. This denotes an increase of the diameter of a vein in a maturated AVF by three times (3 ×6 mm = 18 mm).

Pseudo-aneurysms originating from the anastomosis site are characterized by extravascular haematoma formation after surgery due to improper technique or they can develop later due to repeated needle puncture at the same site or as an infection-related consequence. Puncture of an arteriovenous graft (AVG) or AVF, either during intervention or as part of routine dialysis needling, may cause pseudo-aneurysm development and persistent bleeding. Hospitalizations in haemodialysis patients are frequently caused by arteriovenous complications.

The artery proximal to an AVF routinely dilates as it remodels in response to the increased blood flow⁸. For an AVF's vein to become mature enough for needling, its diameter often dilates by more than three times.

The aetiology of aneurysms is unclear. Repeated needling results in multiple small fibrous scars in the vessel wall, which may expand with time and result in localized aneurysmal areas (Figure 1). In areas where needling has not been performed, aneurysmal dilatation can occur and the high flow through the vessel may result in abnormal shear stress, which promotes outward remodeling and gradual dilation with the grossly increased calibre of the vessel⁹^,¹⁰. Histological examination of resected fistula aneurysms shows extensive infiltration of collagen with thickening and altered architecture of the vessel wall¹¹. Stenoses, which exacerbate abnormal haemodynamics, may be associated with aneurysm formation. Aneurysms can occur downstream of a stenosis, which may be due to the increased transmural pressure or be related to disturbed flow patterns¹². Upstream of a stenosis marked changes in flow patterns occur and can result in pathological remodeling of vessels.

Depending on the shape of the aneurysm Valenti et al. ⁶ categorized AVFAs into four different groups: (Figure 2)

Type 1: Without a “camel hump”

1a: dilatation lengthways along the vein; the vein is uniformly dilated from the site of the arterial anastomosis along the majority or all of its length. The configuration is akin to a hosepipe.

 1b: An aneurysm after the anastomosis; the vein is dilated proximally. This type of aneurysm is usually within 5 cm of the arterial anastomosis. Type 2: With a “camel hump”.

2a: The classic “camel hump”; there is at least one localized venous dilatation. However, more frequently there are two. Hence, the description of a classic “camel hump”. These dilatations emerge at cannulation sites from previous dialysis sessions. The vein is of normal calibre between the locations of the aneurysms but can be stenosed.

2b: A mixture of types 2a and 1b; in other words, a post-anastomotic aneurysm with localized dilations.

Type 3: This class signifies aneurysms that do not have a typical configuration compatible with the description of either type 1 or type 2 AVFAs.

Type 4: These AVFAs clinically appear to be true localized aneurysms but a diagnosis of false aneurysm is confirmed on subsequent duplex imaging.

In asymptomatic patients, mostly conservative management is advocated. The indications for intervention are pain, bleeding, prevention of high output heart failure, steal syndrome etc. The diameter of AVFA and issues related to cosmetics are not indications for surgical intervention. Despite of lack of a strong evidence base concerning which surgical treatment is optimal, to preserve the nature of the AVF, techniques utilizing the native vein is advocated as first-line. According to the literature, good long-term results can be achieved by using aneurysmorrhaphy with or without a prosthetic support. Insertion of a stent graft or surgical ligation of AVFA is recommended for emergency treatment in actively bleeding patients.

The study was a retrospective observational study that was carried out at the Department of Cardiothoracic and Vascular Surgery, IPGMER &SSKM Hospital, Kolkata, from July 2022 to July 2024, 285 chronic kidney disease patients on maintenance hemodialysis, presenting with aneurysm of arteriovenous fistula site were evaluated and all hemodynamically unstable patients were excluded. Detailed history including age, sex, gender, presence of hypertension, diabetes etc. was taken. They were interviewed and examined for any symptoms of swelling, pain, skin over the anastomosis site, or bleeding at their dialysis access site, the role of different blood investigations was evaluated.  Patients were also evaluated based on their available treatment such as endovascular treatment, ligation or excision of pseudoaneurysm etc.

Standard appropriate statistical analysis of the data done

In our study, 24 (8.42%) patients were ≤30 years of age, 42 (14.73%) patients were 31-40 years of age, 66 (23.15%) patients were 41-50 years of age, 97 (34.03%) patients were 51-60 years of age, and 56 (19.64%) patients were ≥61 years of age. 110 (38.59%) patients were female, and 175 (61.40%) patients were male. All patients, i.e.100%, were CKD Stage V receiving dialysis regularly. About 196 (68.77%) patients had brachiocephalic, and 89 (31.22%) patients had radio-cephalic fistula (Table 1).

Among comorbidities, 191(67.01%) patients had T2DM, 246(86.31%) were hypertensive, 183 (64.21%) patients had peripheral arterial disease, 103 (36.14%) patients had heart failure, 236 (82.80%) patients had dyslipidemia. In our study, 190 (66.66%) patients had post-op infection. 108 (37.80%) patients had Type Ia aneurysm, 142 (49.82%) had Type Ib aneurysm, 21 (7.36%) had Type IIa aneurysm, 14 (4.91%) had Type IIb aneurysm

In our study, 128 (44.91%) patients had an asymptomatic type of presentation, while 114 (40%) had bleeding fistula as presentation, and 43 (15.09%) patients had hematoma as presentation. Among treatment modalities, 221 (77.55%) patients underwent surgical ligation of the fistula, 48 (16.84%) underwent excision of aneurysm and repair and 16 (5.61%) patients underwent endovascular repair.

In our study, 128 (44.91%) patients had an asymptomatic type of presentation, while 114 (40%) had bleeding fistula as presentation, and 43 (15.09%) patients had hematoma as presentation. Among treatment modalities, 221 (77.55%) patients underwent surgical ligation of the fistula, 48 (16.84%) underwent excision of aneurysm and repair and 16 (5.61%) patients underwent endovascular repair.

Table 1: Distribution of Age in Group, Sex, Stage of CKD, Type Of AVF, Post operative Infection, Post Op infection, Presence of Type2 DM, Hypertension, Peripheral artery disease, Heart failure, Dyslipidemia, Type Of aneurysm, Presentation of aneurysm

Table 2: Pre-operative blood parameters

Figure 1: Aneurysmal dilation of arteriovenous fistula access

Figure 2: Types of AV Fistula Aneurysm

In literature, the development of aneurysms in patients receiving hemodialysis regularly varies from 6% to 60%¹. However, these figures do not represent the rate of aneurysm development due to inconsistencies in the definition of true, false and pseudo aneurysms in different studies, meaning that these figures represent the total incidence of all types of aneurysms.

AVF created in the upper extremities is the access of choice for patients with renal diseases who need maintenance hemodialysis regularly¹³. One-third of all AVFs at any point in time, develop complications like thrombosis (51.6%), stenosis (22.6%), aneurysm formation (6.7%), and infections (6.5%)¹⁴. Complications of AVFs require hospitalization in 39% of the patients with definitive loss of vascular access in 29%¹⁵.

Risk factors for these complications include the type of fistula, post-operative infection, diabetes mellitus, hypertension, heart failure, arteriosclerosis, dyslipidemia, anaemia, hypoalbuminemia, coagulation disorder and factors related to inappropriate use of the AVF such as early initiation of dialysis through AVF, repeated punctures in the same site, and external mechanical compression. As we found in our study, diabetes mellitus, hypoalbuminemia, hypertension and dyslipidemia were the most common risk factors associated with patients who presented with aneurysms of AV fistula.

Symptomatic AVFA can present with discomfort, profuse bleeding after dialysis, low flow and inadequate dialysis or high flow with a risk of steal syndrome or high output cardiac failure. Bleeding can also occur from rupture of the aneurysm when the skin over the aneurysm becomes progressively thin, necrotic or infected. A review of the literature reveals that important considerations in the management of AVFA include the condition of the overlying skin, the presence or absence of symptoms, difficulty with cannulation, and performance of the AVA. In our study, 40% of the patients presented with bleeding fistula, 15.09% presented with hematoma and 44.91% were asymptomatic. However, surgical ligation of the fistula was done in the majority of the cases, 77.55%, and the most common type of aneurysm found was Type Ib (49.82%).

In our study, out of 285 patients, most of the patients were 51-60 years of age (34.03%), with the male population [175 (61.40%)] higher than the female population [110 (38.59%)].

In our study, all [285(100.0%)] patients were CKD STAGE V. We observed that most of the patients had Brachiocephalic [196 (63.77%)] followed by Radio cephalic [89 (31.22%)] and patients with Brachiocephalic fistulas are more prone to develop complications.

Our study showed that 190 patients had Post-op Infection (66.66%) which seems to play an important role as an etiological factor for aneurysm development.

Among treatment modalities, 221 (77.55%) patients underwent surgical ligation of the fistula, 48 (16.84%) underwent excision of aneurysm and repair and 16 (5.61%) patients underwent endovascular repair, making permanent loss of arteriovenous access a major complication in our study. In our study anaemia, hypoalbuminemia and coagulation disorder seem to have been associated more commonly with patients developing an aneurysm of arteriovenous fistula site. Thus it can be concluded that proper pre-operative optimization of patients with regards to haemoglobin, total protein, serum albumin, total counts, optimization of coagulation profile and prompt management of heart failure can minimize the rate of aneurysm development postoperatively and improve longevity of arteriovenous fistulas for dialysis.

The exact cause of aneurysm development is unclear however aneurysms mostly occur as the venous walls are rather thinner than the arterial wall. Most aneurysms develop at repeated puncture sites for dialysis as the already frail scar tissue of the venous wall is being submitted to repetitive extra strain during repeated punctures. Also, the intraluminal pressure can be too elevated for the thin vessel wall due to high arterial inflow or a venous outflow obstruction due to stenoses.

Paying attention to technical details when creating an AV fistula determines its early and late success rate and longevity. Preoperative optimization of risk factors plays an important role in the prevention of aneurysms and long-term use of arteriovenous fistula for dialysis. The type of aneurysmal development and presentation of aneurysm determines the treatment modality adopted. Asymptomatic AVFAs may be used for dialysis, till symptoms develop preventing its use. According to our clinical experience, repair of the arteriovenous aneurysm should be tried as much as possible. When necessary, only then surgical ligation of the arteriovenous fistula should be done.

Conflict of interest

  None declared

Ethical statement

 Institutional ethical committee clearance not required as the study was a retrospective observational study.

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Abbreviations:

CKD- chronic kidney disease

AVF- Arteriovenous fistula

AVFA- Arteriovenous fistula aneurysm