Background: Orbital lesions represent a spectrum of benign and malignant lesions in adults and children that can be challenging to diagnose and treat. Magnetic resonance imaging is a powerful tool for imaging the orbit, due to the excellent tissue contrast it provides.

Aim: To evaluate the ability of Diffusion-Weighted MRI in the characterization of the orbital lesions.

Patients and methods: We evaluated 50 patients with 25 malignant and 25 benign orbital lesion. MR examinations were performed with a 1.5-T system. Diffusion-weighted single-shot EPI images were obtained in all patients. The apparent diffusion coefficient (ADC) was calculated and correlated with the pathology results.

Results: The mean ADC value of benign and malignant orbital masses was 1.53 ± 0.61 x 10-3 mm2/s and 0.86 ± 0.35 x 10-3 mm2/s, respectively. There was a significant difference in the mean ADC value between benign and malignant orbital masses (P <0.001). The mean ADC value of benign was significantly higher than that of malignant orbital masses, with considering ADC value of 0.90 x10-3 mm2/sec is a cut off between benign & malignant orbital masses by sensitivity 76% and specificity 96%.

Conclusion: We can conclude that the combination of conventional MRI finding and ADC calculation together with clinical finding could improve the diagnostic efficacy of MR imaging in the differentiation between benign and malignant orbital masses with considering an ADC cut off value of 0.90 x10−3 mm2/s between benign and malignant orbital masses with specificity 76% & sensitivity 96%.