Using finite element analysis to obtain the pressure gradient between the left renal vein and the inferior vena cava: a new method for the diagnosis and follow-up of patients with nutcracker syndrome

Background: Nutcracker syndrome (NCS) diagnosis remains challenging due to the lack of non-invasive, reliable methods. Current techniques, including Doppler ultrasound and computed tomography angiography (CTA), lack hemodynamic data, with invasive measurement of the left renal vein-inferior vena cava (LRV-IVC) pressure gradient (true pressure gradient, TPG) being the gold standard. This study aimed to validate a novel non-invasive approach using finite element analysis (FEA) to simulate the LRV-IVC pressure gradient (SPG) to assist in diagnosing and monitoring NCS. Methods: This retrospective study included 46 patients (35 NCS, 11 controls) who underwent CTA and invasive TPG measurement. Patient-specific 3D left renal vein (LRV) models were reconstructed from CTA data using MIMICS and 3-matic software. Hemodynamic simulations were performed via ANSYS (an engineering simulation software) to calculate SPG. Diagnostic performance of SPG and imaging parameters (e.g., beak sign, LRV diameter ratio) was evaluated using receiver operating characteristic (ROC) analysis. Results: 5.5±1.9 mmHg, P>0.05) in NCS patients. Postoperative SPG and TPG decreased comparably (P