MRI study of solitary fibrous tumor in the orbit.

OBJECTIVE: Solitary fibrous tumor (SFT) is a rare lesion of the orbit. The purpose of this study is to determine the MRI features of orbital SFTs.

MATERIALS AND METHODS: We retrospectively reviewed 15 patients with histopathologically proven orbital SFTs. All patients underwent orbital MRI. The location, size, shape, margin, and MRI signal of 15 lesions were reviewed. The time-intensity curve (TIC) of dynamic contrast-enhanced MRI in 14 patients and diffusion-weighted imaging in four patients were also analyzed.

RESULTS: Ten orbital SFTs were located in the extraconal space (seven at the superior aspect and three at the lateral aspect), three in the retrobulbar intraconal space, one in the superomedial aspect of the intraconal space, and one in the lacrimal sac region. All SFTs appeared ovoid in configuration and had well-defined margins. The mean maximum diameter was 30.2 mm (range, 15-56 mm). Fourteen SFTs appeared homogeneously isointense to gray matter on T1-weighted images. On T2-weighted images, the lesions showed heterogeneous isointensity in nine patients and hypointensity in five patients. The lesions showed heterogeneous marked enhancement on contrast-enhanced MRI. Streaky high-signal-intensity areas on T2-weighted images with marked enhancement were observed in nine patients. Flow-void signal was identified in six patients. The TICs of 14 patients showed a washout pattern. The contrast index was 1.61±0.42, the time to peak enhancement was 34.15±14.04 seconds, and the washout ratio was 37.32%±14.37%. The mean apparent diffusion coefficient value of four patients was 1.28±0.23×10(-3) mm2/s. Another case exhibited multicystic appearance.

CONCLUSION: Isointense or hypointense signal on T2-weighted images, marked enhancement, and a washout TIC pattern are the characteristic MRI features of orbital SFTs.