Imaging in Orbital Differential Diagnosis

In reviewing information about the appearance of an orbital lesion on the CT or MR scans, we may classify a lesion being solid or cystic, well circumscribed or ill defined, and localized or infiltrative.1–3 Comparing the density of the lesion with that of the vitreous body will help to identify a solid lesion, whose density is higher than that of the vitreous on CT images. The wide range of signal intensities related to the internal structure and proteinaceous or blood content will not always allow us to differentiate a solid from a cystic orbital lesion (Figure 10.1).2–6 Information obtained from MR images allows us to identify tissue components such as melanin, methemoglobin, deoxyhemoglobin, ferritin, proteinaceous material, and fibrous tissue.1,2–7 Therefore, the clinician will derive more information from the appearance of a lesion from MRI than from CT.