Abstract: Objective：To investigate the effectiveness and safety of endovasculartreatment of inferior vena cava filter thrombosis (IVCFT) during the retrieval window period.Methods：Retrospective analysis of 41 patients with IVCFT who developed IVCFT during the retrieval window from January 2012 to October 2019 in our department through intracavitary techniques such as filter retrieval,catheterdirectedthrombolysis(CDT), mechanical thrombectomy data.Results：5 cases successfully underwent filter retrieval.30 cases underwent CDT treatment. After treatment the review of inferior vena cava angiography showed 21 cases with complete thrombolysis,7 cases with the maximum diameter of residual thrombus ≤1cm,and 2 cases with a maximum diameter 1.7cm and 1.9cm respectively.Filter retrieval was successful in 28 cases.Filter retrieval of 2 cases was abandoned because of residual thrombus being more than 1.5cm. 6 cases received mechanical thrombectomy, of which 3 received mechanical thrombectomyonly. The reviews of inferior vena cava angiography showed their residual thrombus were all less than 1cm, and the filters were successfully retrieved. The other 3 cases received assisted CDT treatment, among which filter retrieval of 2 cases with the maximum diameter less than 1cm was successful and filter retrieval of 1 case with the the maximum diameter 1.7cm was abandoned. The filter retrieval rate was 92.7% (38/41). No related complications occurred during endovascular treatment and filter retrieval. No adverse occurrences during the followup of 41 cases.Conclusion：Filter retrieval, CDT, and mechanical thrombectomy are safe and effective for IVCFT in the retrieval window period,which can effectively improve the filter retrieval rate and avoid various serious complications caused by longterm filter retention.

Key words: retrieval window period, inferior vena cava filter thrombosis, endovascular treatment, filter retrieval rate