White matter: A good reference for the signal intensity evaluation in magnetic resonance imaging for the diagnosis of uveal melanoma.

BACKGROUND Comparing the signal intensity (SI) of an ocular mass to that of the vitreous body has been suggested. Most ocular lesions show a hyper-intense signal compared to the vitreous body on T1-weighted (T1w) images, and malignant melanomas have been almost always determined as 'cannot be excluded' in reports. PURPOSE This study aimed to determine the accuracy of magnetic resonance imaging (MRI) in the diagnosis of uveal melanoma by using normal white matter as reference tissue for SI evaluation on T1w images and vitreous body on T2w compared to the conventional method using the vitreous body as a reference on both T1w and T2w images. METHODS The MRIs of 43 patients (between August 2006 and July 2018) sent to rule out uveal melanoma were blindly reviewed by two radiologists. By using white matter as a reference for SI evaluation on T1w images and vitreous body as a reference on T2w images, uveal melanomas were suggested by hyper-intense signal on T1w and hypo-intense signal on T2w with homogeneous enhancement. The accuracy of diagnosis of uveal melanoma using white matter as a reference on T1w was compared to the conventional method using the vitreous body as a reference on both T1w and T2w images. RESULTS The diagnosis of uveal melanoma using white matter as a reference gave a sensitivity of 92.31% (95% confidence interval (CI) 63.97-99.81) and specificity of 100.0% (95% CI 88.43-100.0). By using the vitreous body as a reference, sensitivity as high as 100.0% (95% CI 100.0-100.0) was obtained, but specificity was low at 53.33% (95% CI 34.33-71.66). CONCLUSIONS White matter is a good reference for the diagnosis of uveal melanoma, with high sensitivity and much higher specificity than conventional methods using the vitreous body as a reference.