Orbital Imaging

In general, MR is superior to CT scanning for demonstrating intracranial involvement of orbital lesions.

FIGURE 7.3. Optic disk photographs show (A) mild optic nerve swelling, (B) more severe optic disk edema, and (C) optic atrophy.

The evaluation of orbital lesions should include orbital imaging [e.g., orbital ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI)].

Retinal artery occlusions may result from orbital infections (e.g., angioinvasive aspergillosis or mu-cormycosis) or in acute orbital trauma (e.g., retro-orbital hemorrhage with elevated intraorbital and intraocular pressure). Intraocular inflammation (e.g., exudative retinal detachment, vitreous cells, retinal in

FIGURE 7.4. Optic disk photographs (A) show optic disk edema and choroidal folds that are seen better on the fluorescein angiogram (B) as alternating light (hyperfluorescent) and dark (hypofluo-rescent) lines. (C) Sagittal T1-weighted MR imaging shows an orbital mass compressing the posterior globe.

CT scans show bony anatomy (e.g., hyperostosis, bone destruction, bone remodeling) and calcifications better than MR scans (Figure 7.5). Fat on Tl-weighted MR studies is hyperintense. Gadolinium contrast is also hyperintense on Tl-weighted images. Fat suppression is necessary for orbital studies in order to visualize any pathologic enhancement. Thus, MR studies of the orbit should be performed with fat suppression techniques and gadolinium contrast material (Figure 7.6). In addition, specific signal characteristics on MRI may help in distinguishing certain tumor types (Figure 7.7).

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