Diffusion-Weighted Imaging of Ocular Melanoma

Objectives: Diffusion-weighted imaging (DWI) allows characterization of masses on the basis of their cellular density. We hypothesized that ocular melanoma has a marked diffusion restriction as seen in other malignant tumors. Furthermore, we aimed to assess whether DWI is useful to differentiate ocular melanoma from retinal detachment. Materials and Methods: The institutional review board approved the prospective study on 44 patients investigated with ocular magnetic resonance imaging including DWI during a 9-month period. A region-of-interest analysis of diffusion-weighted images with b values of 0 and 1000 s/mm(2) was performed to calculate the apparent diffusion coefficient (ADC) of the ocular melanoma and the retinal detachment. Three patients were excluded because DWI was nondiagnostic owing to severe artifacts; in 1 patient, the melanoma was too small for ADC calculation. Therefore, 40 patients were included in the final analysis. Ocular melanomas and detachments were compared with respect to their ADC values. The image quality of DWI was qualitatively scored by 2 readers in consensus on a 3-point scale from 1 (minor artifacts) to 3 (major artifacts). Results: Ocular melanomas showed a marked diffusion restriction, and the mean (SD) ADC was 891 (172) x 10(-6) mm(2)/s. Twenty-nine patients (66%) had retinal detachment. The mean ADC of the ocular melanoma differed significantly (P < 0.001) from the mean ADC of the retinal detachment (1986 [375] x 10(-6) mm(2)/s. The image quality of DWI was rated 1 in 38 patients, 2 in 3 patients, and 3 in 3 patients. Conclusions: Ocular melanoma shows a marked diffusion restriction with an ADC of less than 1000 mm(2)/s, which is in concordance with other malignant tumor entities. Diffusion-weighted imaging helps differentiating ocular tumors from retinal detachment and should therefore be included in the ocular magnetic resonance imaging protocol if an ocular mass is suspected.