Background <p>Previous studies exploring preoperative intrahepatic portal venous system to evaluate Rex shunt efficacy in pediatric cavernous transformation of the portal vein have yielded controversial results.</p> Objective <p>To develop a novel postoperative intrahepatic portal venous system classification to predict long-term outcomes of Rex shunt in children with cavernous transformation of the portal vein.</p> Materials and methods <p>From October 2014 to February 2024, children with cavernous transformation of the portal vein who underwent Rex shunt were retrospectively analyzed. One week after Rex shunt, intrahepatic portal venous system were classified into types A-C using ultrasound based on the patency of the connection between the Rex vein and the right portal vein. These types were further subdivided into subtypes based on the Rex vein inner diameter. We compared spleen length, spleen thickness, and esophageal variceal grading before and one year after Rex shunt across these types, as well as the incidence of vascular complications one year after Rex shunt.</p> Results <p>The study included 160 children: 129 type A (124 type A1, 5 type A2), 25 type B (17 type B1, 8 B2), 6 type C1, with subtypes distinguished by an Rex vein inner diameter ≤ 4&#xa0;mm. Type A exhibited superior outcomes compared to types B and C, which had comparable results. Type A1 demonstrated the most significant benefits, with fewer complications and improved variceal grading, although splenic size reduction was similar to that of type B1. Type B1 outperformed type B2 in terms of complications, variceal grading, and splenic measurements, and surpassed type A2 in splenic length reduction and type C1 in variceal grading and splenic thickness reduction.</p> Conclusions <p>The novel one-week postoperative intrahepatic portal venous system is effective to predict one-year postoperative outcomes of Rex shunt.</p>