EUS-fine needle aspiration for computed tomography-detected retroperitoneal nonmass lesions after failed or infeasible percutaneous biopsy: A 2-center comparative study

Background and Objectives: Retroperitoneal nonmass lesions (NMLs) present significant diagnostic challenges due to their ill-defined margins and subtle radiographic features. This 2-center study evaluated the diagnostic efficacy and safety of EUS-fine needle aspiration (FNA) for NMLs following failed or infeasible percutaneous biopsy, comparing its performance with that of EUS-FNA for mass lesions (MLs). Methods: We retrospectively reviewed 206 patients from January 2021 to April 2024 undergoing EUS-FNA for retroperitoneal lesions. The study cohort comprised an NML group ( n = 60), consisting of cases identified by contrast-enhanced computed tomography where percutaneous biopsy had failed or was technically infeasible, and a control ML group ( n = 146). Primary endpoints were diagnostic accuracy, sensitivity, and specificity. Secondary endpoints included rates of histologic inadequacy, procedure-related complications, and the need for repeat biopsy. Results: The NML group achieved a diagnostic accuracy of 90.0%, sensitivity of 89.1%, and specificity of 92.9%, demonstrating no significant difference compared with the ML group (89.0%, 86.8%, and 100%, respectively; all P > 0.05). No significant intergroup differences were observed in histologic inadequacy (6.7% vs. 10.3%, P = 0.597), complication rates (5.0% vs. 6.8%, P = 0.760), or repeat biopsy rates (8.3% vs. 6.2%, P = 0.555). Outcomes remained comparable across all subgroups stratified by baseline characteristics (all P > 0.05). Conclusions: EUS-FNA is a reliable and safe modality for the evaluation of morphologically indistinct retroperitoneal lesions. When percutaneous biopsy is unsuccessful or technically prohibitive, EUS-FNA provides diagnostic yields comparable to those achieved for MLs.