Procedural complications will be categorized into two main groups: transplant complications and procedural complications related to endovascular or surgical revascularization for HAC. Within these groups, intra-procedural complications predominantly consist of vascular issues, such as thrombosis, stenosis, compression, dissection, and rupture. In contrast, post-procedural complications encompass a broader range of issues, such as infection, rejection, bleeding, and vascular and biliary complications, including anastomotic stricture, non-anastomotic strictures, bile leak, biloma, or cholangitis. Re-interventions addressing both intra- and post-procedural complications will also be recorded.

Anticoagulant therapy after transplantation and after interventions for HAC will be assessed according to the management practices of each participating site (center specific) and individual patient data (patient specific). Details about each anticoagulation regimen, including the specific anticoagulant, duration of anticoagulation, and upper and lower limits of target values, such as international normalized ratio, anti-factor Xa, and activated partial thromboplastin time, will be recorded. Patient-specific management will be documented for patients with HAC.

Local screening protocols to assess HAC after LT, such as the routine post-operative Doppler ultrasound policy, will be documented. Whether HAC screening is consistent for patients with and without risk factors will also be examined. The frequency of preferred radiological screening investigations within 2 weeks after LT will be determined, considering various risk factors.

The diagnostic criteria section will cover the types of HAC, non-invasive radiological criteria, and interventional radiological criteria during invasive angiography. The center's definition of technical success after interventional radiological treatment will also be recorded.

The radiological follow-up section will assess whether follow-up protocols are the same for all interventions or specific to each intervention type. The imaging methods and frequencies of radiological follow-up for different treatment modalities will be determined. Additionally, the experience years and level of seniority of the interventional radiologist will be recorded.

The incidence of HAC will be determined by dividing the total number of patients diagnosed with HAC between 1st of January 2002 and 1st of January 2023, who had undergone LT between 1st of January 2002 and 1st of January 2022, by the total number of patients who underwent LT at pediatric age between 1st of January 2002 and 1st of January 2022. The study will present the overall incidence of HAC during the 20-year period of 2002 to 2022, as well as the incidence during specific 5-year intervals, namely 2002 to 2007, 2007 to 2012, 2012 to 2017, and 2017 to 2022, for each complication.