Magnetic Resonance Imaging and DWI Features of Orbital Rhabdomyosarcoma

Purpose: To describe the magnetic resonance imaging(MRI)features of orbital rhabdomyosarcoma(RMS).Methods: Thirty-nine patients with histopathologically confirmed orbital RMS were retrospectively reviewed. All patients underwent orbital conventional MRI, including axial, sagittal,and coronal T1-weighted, T2-weighted, and postcontrast T1-weighted sequences. The location, shape, margin, and MRI signal of the 39 lesions were reviewed. DWI in 15 patients and susceptibility weighted imaging(SWI) in 2 patients were also analyzed.Results: Orbital MRI was available in 39 patients and revealed a soft tissue mass in the orbital region in all cases. Of the 39 patients, the primary tumor sites were limited to the orbital proper in 31 cases, while 28 cases had extraocular muscle invasion and 8 cases had extraorbital invasion. All lesions were unilateral. Thirty-three cases were well-defined soft tissue masses and 6 cases appeared as less well-defined softtissue masses. Thirty-four cases showed homogeneous isointense or slightly hypointense signals on T1-weighted imaging(T1WI) and hyperintense signal on T2-weighted imaging(T2WI) compared with extraocular muscles. Five cases had heterogeneous signals with focal areas of increased signal on T1WI or decreased signal on T2WI, including 1 case with hypointense signal on SWI. The mean apparent diffusion coefficient(ADC) value of the viable part of tumors was(0.925±0.09)×10-3mm2/ s. All cases showed moderate to marked enhancement after contrast administration.Conclusion: Several MRI features-including homogeneous isointense or slightly hypointense signal on T1WI and slightly hyperintense signal on T2WI, relative low ADC values, and moderate to marked enhancement, extraocular muscles invasion, and extraorbital extensionare helpful in the diagnosis of orbital RMS.