Periorbita: Computed tomography and magnetic resonance imaging findings

Purpose: The periorbita has been regarded as the critical structure in decision of exenteration in the patients with paranasal (PNS) malignancies. The purpose of this study is to present the CT and MRI findings of the periorbita with PNS malignancies. Materials and Methods: Ten patients with PNS cancers were chosen for this study. PNS CT and MRI scans were performed on all patients. The imaging findings were reviewed retrospectively by consensus of two neuroradiologists. Assessment of the defect of the orbital bone and invasion of the orbital fat was made by CT and MRI. The signal intensity (SI) thickness, enhancement, and correlation with the orbital bone of the periorbita were analyzed on MRI. The intraoperative and pathologic reports were used as the gold standard for orbital invasion. Results: In patients with bone defects, it was impossible to differentiate the periorbita from the mass on CT. The periorbita showed hypointensity on T2-weighted images compared with the SI of mass. On Gd-enhanced T1-weighted images, the periorbita showed less enhancement than the mass in nine patients. Six patients showed two hypointense layers (the outer bony wall and the inner periorbita) between the mass and orbital fat on T2-weighted images. The thickness of the periorbita was 0.79-1.4 millimeter. Orbital invasion was more conspicuous on T2-weighted coronal images than on the CT images. Conclusions: MRI was more conspicuous for detecting orbital invasion than CT. The mass beyond the thickened periorbita on T2-weighted images was considered to be a positive finding of orbital invasion.