VALUE OF MRI (DWI &ADC) IN DIFFERENTIATING BENIGN AND MALIGNANT ORBITAL LESIONS

Abstract

rbital and intraocular masses are relatively uncommon compared to other mass lesions of the body. It has been described that two-thirds of orbital tumors are benign and one third is malignant. Differentiating between these causes based on clinical findings may be difficult. Some lesions can be diagnosed easily depending on their characteristics on MRI such as typical location and enhancement pattern, but sometimes their characterization is still difficult. Diffusion weighted imaging (DWI) is an advanced MR-based technique which has the ability to characterize and differentiate morphologic features, including edema, necrosis, and tumor tissue, by measuring differences in apparent diffusion coefficient (ADC) caused by water proton mobility alterations and so can aid in differentiation of malignant and benign orbital lesions, which is focal to planning further patient management. Results of this study shows that there was significant association between signal intensity of DWI, ADC maps and nature of the orbital lesions. By assessment of ADC values, malignant masses had significantly lower ADC value than benign lesions. Careful positioning of the ROIs within the solid, non-necrotic, non-cystic, non-calcified and non-hemorrhagic tumors’ parts appears to be essential in achieving accurate results. Results of this study also showed that the ADC values of lymphomas were markedly lower than those of orbital pseudotumor with no overlap found between their ADC values, an observation which is particularly valuable as these two pathologies are often difficult to differentiate by conventional MR sequences alone.