The roles of the diffusion-weighted imaging in orbital masses.

Introduction: Causes of orbital masses can be either benign or malignant. An MRI with diffusion-weighted imaging (DWI) may be helpful to differentiate causes of orbital masses. This study aimed to evaluate the diagnostic properties of an apparent diffusion coefficient (ADC) in orbital masses.

Methods: We retrospectively reviewed patients with orbital masses who underwent DWI and had histopathological results. Orbital lesions were categorized as benign or malignant and compared with respect to the ADC and ADC ratio. A receiver operating characteristic curve (ROC) was plotted to evaluate the sensitivity and specificity of the ADC and ADC ratio threshold.

Results: The mean age of all 42 patients in this study was 36.31 years (S.D. 22.12) and 26 of the patients were male (61.9%). The malignant orbital masses accounted for 43% (18 patients). The most common cell type was meningioma (10 patients; 23.8%). There was no statistical difference between the ADC values of benign and malignant tumours (1.18 vs 0.99 ×10  mm /s; P-value 0.200). The myxoid tumours had significantly higher ADC values than the non-myxoid (1.58 vs 0.99; P-value 0.008) tumours. Non-metastatic non-myxoid tumours also had significantly lower ADC values than metastatic non-myxoid tumours (0.73 vs 1.32; P-values 0.006). The ADC cut-off point of greater than or equal to 0.95 × 10  mm /s was given a sensitivity of 87.50% for myxoid orbital masses, while the cut-off point of greater than or equal to 1.01 × 10  mm /s was given a sensitivity of 80.00% for metastatic, non-myxoid malignant orbital masses.

Conclusions: Benign and malignant orbital masses cannot be distinguished by using the ADC values. However, the ADC values were useful in differentiating between myxoid vs non-myxoid orbital masses and metastatic non-myxoid vs non-metastatic non-myxoid orbital masses.