The incidence and prevalence of AV access aneurysms are not clearly defined, partially due to the inaccurate and inconsistent criteria. Balaz and Bjorck(4) defined an AVF aneurysm as a dilation of all three vascular layers with a diameter of > 18 mm or roughly three times the diameter of the outflow vein of a mature AVF. There are also other classifications due to the lack of consensus(13). Aneurysms can form anywhere along the AV access, including the inflow artery(14), but they are commonly located in the outflow vein. The hemodynamic changes induced by AV access creation causes AV access dilatation. Hemodynamic alterations are possibly aggravated by recurring canulations and vascular wall damage, and they can lead to aneurysms when combined with high intra-luminal pressures from any outflow stenosis. The skin of aneurysms tenuate constantly and break easily with hemorrhage; aneurysms also cause AV access disfunction, pain, and canulation difficulties. The size of an AV access aneurysm alone is not enough to warrant surgery(4). According to KDOQI, it is reasonable to obtain emergent surgical procedure for AV access aneurysm complications such as erosion or hemorrhage (Expert Opinion)(11). Aneurysms can induce AV access thrombosis, which is the leading cause of AVF disfunction. Thrombosis is also one of the reasons for discarding an aneurysmal AVF(7).
Access thrombosis can be managed using surgical procedures and endovascular technology, although both have certain shortcomings for aneurysmal AV accesses with thrombi. There are no randomized controlled trials comparing endovascular with surgery procedures for thrombosed aneurysmal fistulas, and the quality of the pertinent evidence to guide therapy is poor. According to KDOQI, open surgical procedure should be considered the standard treatment for AV access aneurysms, with the specific approach determined based on native expertise (Expert Opinion). The procedure may include a scheme for staged restoration of various aneurysms to avoid implanting a central venous catheter during the perioperative period(11). However, there are no recommendations for thrombosed aneurysmal fistulas.
Interventional therapies consist of mechanical thrombectomy, manual catheter aspiration, fibrinolysis, and/or removal of the thrombus with a balloon catheter. The aforementioned techniques can be used to perform PTA and stent placement of underlying lesions. Ahn(15) reported on sixteen patients who had endovascular recanalization of a thrombosed native AVF combined with an aneurysm. Mechanical thrombectomy was used for recanalization, followed by additional treatments. Balloon angioplasty was used for all stenoses in 15 patients (93.8%), and stents were inserted in two patients (12.5%) because of central vein stenoses. All patients had outflow draining vein stenoses, five patients (31.8%) had AV anastomosis and juxta-anastomosis stenoses, and three patients (18.8%) had central vein stenoses. The primary patency rates at three, six, and twelve months were 70.5%, 54.8%, and 31.3%, respectively, whereas the secondary patency rates were 70.5%, 70.5%, and 47.0%, respectively. In this study, the 12-month primary patency rate was relatively low, whereas the secondary patency rate increased to 47%. However, if recanalization was successful, subsequent interventional treatment can often prolong the lifetime of a aneurysmal AVF. We used ultrasound as a preoperative examination method, while the operation was guided by fistulography. The aneurysmal section was not used as a canulation site, although we took advantage of aneurysms as an endovascular intervention puncture site. Additionally, the type of AVF was mainly upper-arm brachiocephalic (87.5%), as opposed to our study (100% forearm AVF), and the detailed information of aneurysms and thrombus, particularly the measurement data of the color Doppler ultrasound is not mentioned.
Recently, “Stent tunnel technique”, which is a novel endovascular treatment technique of inserting nitinol auto-expandable uncovered stents stretching through the whole puncture site area, thereby creating a tunnel inside the thrombus, was reported to salvage thrombosed native AVF with extensive aneurysm(16). The stent tunnel technique was used to treat a 10 patients with native fistulas in whom flow restoration could not be achieved via conventional percutaneous techniques. The mean follow-up period was 167 days (60–420 days), with a primary and assisted patency rates of 80% and 100%, respectively. The results could not be further interpreted due to the short follow-up and incomplete vascular access characteristics. According to KDOQI, covered intraluminal stents (stent-grafts) may be used as an alternative to open surgical repair of AV access aneurysms/pseudoaneurysms only in special circumstances such as patient contraindication to surgery or lack of surgical option, due to the associated risk of infection in this scenario. Canulation over the stent-graft segment should be avoided when possible (Expert Opinion)(11).
The latent drawbacks of using an intra-luminal stent include the latent size mismatch between the inflow and outflow segments, latent loss of canulation area (as well as infection risk of surrounding nonresorbable chronic thrombus), and lack of compatibility within the aneurysm. Furthermore, stent grafts are not designed for repetitious canulation and are not officially authorized by the America Food and Drug Administration for AV access salvage. Zink et al.,(17) reported a 29% complication rate with the use of stent grafts for salvaging AV access, which included aneurysms/pseudoaneurysms and specific complications such as migration, fracture, erosion, and rupture.
Lambert(18) compared open surgical and radiological interventions for thrombosed arteriovenous access and found that interventional radiological thrombectomies had a lower primary failure rate and better assisted primary patency than surgical thombectomies. However, interventional radiological thrombectomies had a lower intervention-free survival rate and required additional procedures to maintain patency. Hybrid procedures were introduced in the treatment of AV access with aneurysm in previous studies(10,19). The treatment consists of the open and endovascular steps, which are performed separately. Hybrid procedures are less invasive compared to open surgery, allowing for multi-site treatment of various concurrent stenoses and aneurysms located in diverse sections of the fistula, as well as the preservation of an extended section of dialysis fistula accessible for canulation. The results of the mentioned studies demonstrated that performing surgical AV access aneurysm excision and endovascular stenosis angioplasty simultaneously was highly effective and efficient.
Joo SM(20) reported a novel technique of minimally invasive approach in the recanalization of thrombosed aneurysmal AVF, in which a small incision was made on the enlarged aneurysm, and thrombi were removed with forceps and Fogarty catheters via the incision site. A balloon catheter was inserted through the incision site to perform balloon angioplasty when significant stenosis was found. In this study, an aneurysm was defined as being twice the size of a normal section of the fistula, and ultrasound and fistulography were performed during the procedure. Similarly, the characteristics of thrombosed aneurysmal fistulas were not explicitly defined. The duration of follow-up period ranged from 2 to 32 months (mean: 12 months; median: 10.5 months). Primary patency rates were 92% after three months, 68% after six months, and 19% after 12 months. Secondary patency rates were 100% after three months, 100% after six months, and 92% at 12 months. High technical success and secondary patency rates were achieved in these patients. Minimal venotomy combined with endovascular treatment was proved to be a safe approach for the recanalization of thrombosed aneurysmal AVF with minor complications.
Our study has unique characteristics compared with the previous studies. First, our patients had more severe thrombotic events, with one patient experiencing a thromboembolism emergency. The timing of thrombus formation, the thrombus length, and aneurysm size were all accurately recorded. The mean aneurysm maximal diameter was 21.5 mm (standard deviation: ± 5.0 mm) and the mean thrombus length was 12.9 cm (8–22 cm). One patient had thrombosis for 18 days (432 hours) and was successfully recanalized. In our experience, the time of thrombus formation did not seem to be an absolute contraindication for endovascular procedures, and most of the patients could be recanalized provided that calcification thrombosis is not combined.
Second, all of our patients had forearm AV fistulas, which could be explained by the low proportion of upper arm fistulas in our hospital. If the forearm AV fistulas failed, a prosthetic vascular graft in the forearm was preferred. Third, duplex scanning was the exclusive imaging modality during the procedure. The Doppler color ultrasound allows for a more precise visual image of the thrombus than radioscopy, aiding in the prevention of blood vessel embolism when working in the anastomotic space. Ultrasound decreases radiation exposure for the patient and, most importantly, for the personnel by allowing for shorter durations for radioscopy. Although sonography cannot provide the same panoramic image of the fistula as radioscopy, we believe that a comprehensive and careful evaluation of preoperative color Doppler Ultrasound and skilled ultrasound techniques can compensate for this flaw. It is also challenging to locate the guide into the vena subclavia using sonography, and central veins stenoses are difficult to see with ultrasound imaging; in these cases, radioscopy may be required.
Fourth, three major complications occurred in the same patient, including post-procedural thrombosis and fistula rupture secondary to incision infection. Repeated incisions at the same aneurysm site, as well as prolonged operation time, may have caused incision infection. The immediate postoperative rethrombosis was due to the negligence in evaluating the stenosis during the procedure. The degered to which the stenotic segments were dilated will also have an important impact on the long-term patency rate of the aneurysmal fistulas. In this group of cases, one patient had rethrombosis in the fourth month of follow-up, and another had decreased fistula blood flow in the third month; re-intervention was basically linked to the restenosis.