BACKGROUND: Little guidance exists for the treatment of pseudoaneurysm following pediatric blunt liver and/or spleen injuries (BLSI). We aimed to describe the incidence of delayed pseudoaneurysm development and the subsequent clinical course of pseudoaneurysm in pediatric BLSI. METHODS: This multicenter retrospective cohort study from Japan included pediatric patients (≤16 years old) who sustained BLSI from 2008 to 2019. The cohort was divided into four groups based on hemostatic intervention within 48 hours of admission, namely non-operative management (NOM), NOM with interventional radiology (IR), operative management (OM), and combined IR/OM. Descriptive statistics were used to describe the incidence of delayed pseudoaneurysm among the groups and to characterize the clinical course of any pseudoaneurysms. RESULTS: A total of 1, 407 children (median age, 9 years) from 83 institutions were included. The overall number (incidence) of cases of delayed pseudoaneurysm formation was 80 (5.7%), and the number with delayed pseudoaneurysm rupture was 16 (1.1%) cases in the entire cohort. Patients treated with NOM (1056), NOM with IR (276), OM (53), and combined IR/OM (22) developed 43 (4.1%), 32 (12%), 2 (3.8%), and 3 (14%) delayed pseudoaneurysms, respectively. Among patients who developed any pseudoaneurysms, 39% of patients underwent prophylactic IR for unruptured pseudoaneurysm, while 13% required emergency angioembolization for delayed pseudoaneurysm rupture, with one ruptured case requiring total splenectomy. At least 45% of patients experienced spontaneous resolution of pseudoaneurysm without any interventions. CONCLUSION: Our results suggest that the risk of delayed pseudoaneurysm still exists even after acute phase IR as an adjunct to NOM for BLSI in children, indicating the necessity of a period of further observation. While endovascular interventions are usually successful for pseudoaneurysm management, including rupture cases, given the high incidence of spontaneous resolution, the ideal management of pseudoaneurysm remains to be investigated in future studies. LEVEL OF EVIDENCE: Level 4; Therapeutic/Care management
