Diffusion-weighted imaging for the differentiation of Ewing sarcoma from osteosarcoma

Objective: The purpose of this study is to assess the ability of apparent diffusion coefficient (ADC) values in differentiating Ewing sarcoma and osteosarcoma. Materials and methods: This retrospective cross-sectional observational study included a total of 35 patients with a recent diagnosis of Ewing sarcoma (n = 13) and osteosarcoma (n = 22) who underwent conventional MRI and diffusion-weighted imaging (DWI). Three ADC measurements from the areas of the lowest diffusivity in ADC maps (ADC_min), and other areas with low diffusivity (ADC_other), were made independently by two observers on pre-treatment MRI, and the means of these measurements were compared using independent samples t-test. Intraclass correlation coefficient was calculated for inter-observer agreement. Results: There was a significant difference between the ADC_min (P < 0.001) and ADC_other (P < 0.001) in Ewing sarcoma and osteosarcoma for both observers. For Ewing sarcoma and osteosarcoma, mean ADC_min was 0.566 ± 0.07 and 1.193 ± 0.33 × 10⁻³ mm²/s; 0.551 ± 0.08 and 1.182 ± 0.33 × 10⁻³ mm²/s; and mean ADC_other was 0.813 ± 0.11 and 1.510 ± 0.35 × 10⁻³ mm²/s; 0811 ± 0.12 and 1.501 ± 0.33 × 10⁻³ mm²/s for observers 1 and 2, respectively. Inter-observer correlation coefficient for mean ADC_min was 0.994 and for mean ADC_other was 0.995. Conclusion: Diffusion-weighted imaging and ADC values could be used in the differentiation of Ewing sarcoma and osteosarcoma in borderline cases.