Purpose: To evaluate the utility of absolute and relative apparent diffusion coefficient (ADC and ADCr) in differentiating orbital lymphoma from other orbital lesions.
Design: Retrospective observational study.
Participants: Thirty-Three Patients (33) presenting with orbital masses.
Methods: Magnetic Resonance Imaging (MRI) studies were analyzed, with calculation of absolute ADC and ADCr values. Brainstem ADC measured on the same axial plane was used as the reference for ADCr calculation. ADC and ADCr values were compared between lymphoma and non-lymphoma groups using the Mann–Whitney U test.
Main Outcome Measures: Absolute ADC and ADCr values and their diagnostic performance.
Results: Lymphomas demonstrated significantly lower ADC and ADCr values compared to non-lymphoma lesions. Median absolute ADC was 0.65 × 10?³ mm²/s (Interquartile Range [IQR]: 0.59 - 0.70) in the lymphoma group and 1.32 × 10?³ mm²/s (IQR: 1.11 - 1.57) in the non-lymphoma group. Median ADCr values were 0.86 (IQR: 0.81 - 0.92) and 1.63 (IQR: 1.35 - 1.92), respectively (p < 0.001 for both comparisons). Using a cutoff value of 1.0, absolute ADC showed higher sensitivity, whereas ADCr demonstrated higher specificity, positive predictive value, and overall accuracy.
Conclusions: Absolute and relative ADC values are useful, non-invasive imaging parameters for differentiating orbital lymphoma from other orbital lesions. Relative ADC, using the brainstem as a reference tissue, may represent a valuable complementary approach by reducing interindividual variability and improving lesion discrimination.