Refractory perirenal effusion in a pediatric patient with antithrombin III deficiency and KILT syndrome: a case report.

Congenital antithrombin III (ATIII) deficiency is a rare hereditary thrombophilia that is caused by SERPINC1 variants. Reports on KILT syndrome, which is defined by the triad of kidney anomaly, inferior vena cava (IVC) anomaly, and leg thrombosis, have been sporadic. We described the case of a 10-year-old boy with a solitary left kidney and IVC agenesis who carried compound heterozygous variants in SERPINC1. He presented with flank pain due to renal infarction and subsequently developed massive perirenal effusion. Despite anticoagulation and prolonged percutaneous drainage, the effusion persisted and was confirmed to be of lymphatic origin. Imaging revealed abnormal lymphatic flow related to venous hypertension in the renal hilum. Complete resolution of the effusion was achieved following four sessions of ethanol sclerotherapy. To the best of our knowledge, this was the first reported case of ATIII deficiency complicated by refractory perirenal lymphatic leakage. The case suggested a potential link between thrombosis and secondary lymphatic dysfunction and demonstrated the effectiveness of repeated sclerotherapy for refractory perirenal effusion. Early recognition of hypercoagulable states in children with IVC and renal anomalies is crucial for the prevention of thromboembolic events.