Comparative assessment of diseases of the orbit using computed tomography and magnetic resonance imaging.

Computed tomography (CT) and magnetic resonance imaging (MRI) are the modalities of choice in the assessment of inflammatory diseases, cysts, benign and malignant tumors found in the orbit. CT delineates, to greater advantage, bony structures and areas of calcification. MRI is superior to CT in visualization of the various soft tissue structures and in providing lesion characterization. The lesion location in the orbit is important: extraconal (frequently lymphomas), intraconal (most commonly cavernous hemangiomas and neurilemmomas), and optic nerve sheath (gliomas and meningiomas). The contours of the lesion are also significant: sharply delineated (benign), irregular, lobulated (lymphoma or lymphoid hyperplasia), or invasive (paranasal tumors). CT and MRI characteristics, in particular contrast enhancement, further contribute to the characterization of the various types of lesions within the orbit.