The incidence and prevalence of AV access aneurysms are not clearly defined, partially due to the inaccurate and inconsistent criteria. Balaz and Bjorck  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, we adopted their definition of AVF aneurysm in our study. There are also other classifications due to the lack of consensus . Aneurysms can form anywhere along the AV access, including the inflow artery , but they are commonly located in the outflow vein. KDOQI guidelines 2019 suggested AV access aneurysms be divided into 6 types based on their locations and numbers . 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. 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 .
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 . However, there are no recommendations for thrombosed aneurysmal fistulas.
Ahn  reported on sixteen patients who had endovascular recanalization of a thrombosed autologeous 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. In our study, We used duplex scanning as a preoperative examination method and intraoperative real-time monitor, while they were 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 autologeous AVF with extensive aneurysm . They reported good patency rates,but the results could not be further interpreted due to the short follow-up and incomplete vascular access characteristics. Zink et al  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  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.
Joo SM  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. 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..
Our study has unique characteristics compared with the previous studies. First, our patients had more severe thrombotic volume, with one patient experiencing a thromboembolism emergency. 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.
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 degree 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.
Our study has a couple of limitations. First, it was a retrospective study, which suggests that certain events may have been missed throughout the follow-up period. Second, our research only included a small number of patients, and the study period was brief. Despite these limitations, our technical success rate, short-term primary patency, and secondary patency were comparable to those reported in previous studies. Nonetheless, the sample size should be increased in future research and continue with collection of follow-up data in order to analyze long-term patency rates. Finally, because this was not comparative study, a comparison between surgical strategies and our approach is required in the future.