MR imaging of malignant uveal melanoma: role of pulse sequence and contrast agent

To determine the most sensitive pulse sequence and to clarify the role of each pulse sequence in the MR diagnosis of uveal malignant melanoma, noncontrast T1- and T2-weighted, and postcontrast T1-weighted, spin-echo images were compared blindly and independently by two experienced observers. Thirty uveal malignant melanomas, preselected by ophthalmoscopy and sonography for size greater than 2 mm, were examined with a 1.5-T superconducting MR unit with an orbital surface coil. Fifteen tumor studies were done after the patient was injected with gadopentetate dimeglumine. Postcontrast T1-weighted images were the most sensitive in detecting melanomas, demonstrating tumors 2 mm in height accurately on axial planes and 1.6 mm in height on combined orthogonal planes. The contrast-to-noise ratio between melanoma and vitreous fluid was greatest on postcontrast T1-weighted images (average, 72.1), followed by noncontrast T1-weighted images (average, 32.9), and then by T2-weighted images (average, -21.2). Postcontrast T1-weighted images also proved useful in differentiating melanomas from subretinal fluid collections when combined with noncontrast images. We conclude that postcontrast T1-weighted images are most helpful in detecting small uveal melanomas and in differentiating melanomas from subretinal fluid collections.