Purpose: Retinal pigment epithelium (RPE) adenoma is a rare intraocular benign tumor. It is almost always misdiagnosed as uveal melanoma (UM) resulting in inappropriate management. The purpose of this study was to investigate MRI features of the RPE adenoma that may help differentiate this entity from UM.
Methods: MRI was performed in eight patients with pathology-proven RPE adenoma, five of whom had dynamic contrast-enhanced (DCE) MRI. The time-intensity curves (TIC) of all DCE-MRI were evaluated, and the maximum contrast index (CImax) were calculated.
Results: All eight tumors showed well-defined margins. They were homogeneously hyperintense on T1WI and hypointense on T2WI compared to vitreous body. An oval mass was seen in five tumors, lentiform in two tumors, and placoid-shaped in one tumor. After contrast administration, mild enhancement was identified in five tumors and moderate enhancement in three tumors. In all five tumors, DCE-MRI exhibited a plateau-shaped TIC with a median CImax of 0.37. A "dark-linear sign" (defined as low signal intensity linear zone located between tumor and enhanced choroid on post contrast T1WI with fat-suppression) was noted in all eight patients with RPE adenoma.
Conclusion: RPE adenoma and UM often have similar MR imaging findings. This study reports for the first time a "dark-linear sign" on post contrast T1WI with fat-suppression seen in RPE adenoma. This observation may be characteristic of RPE adenoma and may help separate this entity from UM.
Keywords: Adenoma; Diagnosis; Magnetic resonance imaging; Retinal pigment epithelium; Uveal melanoma.