Role of magnetic resonance diffusion-weighted imaging in differentiating lacrimal masses.

Purpose: To evaluate the role of magnetic resonance (MR) diffusion-weighted imaging (DWI) in discriminating lacrimal masses, including neoplastic and nonneoplastic entities. Materials and Methods: Forty-four patients with lacrimal masses underwent conventional MRI and DWI. The apparent diffusion coefficient (ADC) values of each mass and the ipsilateral temporal lobe were measured and the ratios of the lesion to temporal lobe ADC were calculated. Results: Pleomorphic adenomas had significantly higher ADC values (1.37 +/- 0.22 x 10(-3) mm(2)/sec) and ADC ratios (1.85 +/- 0.34) than malignant tumors (1.03 +/- 0.19 x 10(-3) mm(2)/sec, 1.37 +/- 0.27) (P < 0.001), inflammatory pseudotumors (0.9 +/- 0.08 x 10(-3) mm(2)/sec, 1.19 +/- 0.07) (P < 0.01), reactive lymphoid hyperplasias (RLHs) (0.6 +/- 0.06 x 10(-3) mm(2)/sec, 0.79 +/- 0.07) (P < 0.001), and lymphomas (0.55 +/- 0.06 x 10(-3) mm(2)/sec, 0.74 +/- 0.08) (P < 0.001). RLHs and lymphomas had significantly lower ADC values and ADC ratios than malignant tumors (P < 0.05) and inflammatory pseudotumors (P < 0.05). An ADC value of less than 1.14 x 10(-3) mm(2)/sec and an ADC ratio of less than 1.6 were optimal for differentiating malignant tumors from benign tumors (sensitivity: 80 and 90%, specificity: 100 and 88.9%, respectively). An ADC value of less than 0.76 x 10(-3) mm(2)/sec and an ADC ratio of less than 1.0 were optimal for distinguishing lymphoproliferative disorders from inflammatory pseudotumors (sensitivity: 100%, specificity: 100% for both). Conclusion: DWI can help differentiate lacrimal masses and provides a potential clinical tool for noninvasive tissue characterization.