Radiological Pitfalls in DWI in Characterization of Primary Retroperitoneal Masses

Abstract Background: Retroperitoneal space is the seat of different masses with a wide range of differential diagnosis. MRI is the best modality in soft tissue characterization of these masses after an organ of origin has been excluded. Functional assess-ment by diffusion-weighted MRI and ADC maps is of added value in prediction of tumor nature in cases with equivocal conventional mri results. Several studies investigated the accuracy of DWI in differentiating benign and malignant retroperitneal lesions. Aim of Study: To identify causes of false results in DWI assessment in retroperitoneal lesions aiming for higher accuracy of results and reach optimal cut off point to differentiate benign and malignant lesions. Patients and Methods: The study included 48 patients presenting with retroperitoneal masses, conventional MRI was performed with pre and post contrast sequences together with DWI, results were correlated with pathological results. Data were coded using the statistical package for the Social Sciences (SPSS) version 28. Results: The study included 48 patients, presenting with retroperitoneal masses where 60.4% proved malignant and 39.6% proved benign or non neoplastic lesions. Sarcomas were the most common tumor representing 35.4% of all cases. 26.3% of benign tumors had restricted diffusion while 3.4% of malignant cases had facilitated diffusion. A cut off value of 0.9085x10-3 mm2/sec. was determined cases with false results were reexamined to identify pitfalls. Conclusion: Diffusion weighted sequences are an added value to conventional MRI, differentiating benign and malig-nant lesions. Pitfalls in the application of DWI should be emphasized and avoided. This include sufficient patient clinical data, understanding the cellularity of different lesions and tumors and the effect of treatment on it, avoiding subjective DWI evaluation without conjunction with ADC quantitative assessment.