What to Order
With some important exceptions (see Tables 2-1, 2-4), MRI is usually more valuable than CT in detecting a lesion and narrowing the differential diagnosis. The specific choice of imaging modality, including the sequence, orientation, and direction, depends on a combination of the suspected location and the expected pathology. In suspected large-vessel disease, MRA, CTA, and DSA may also be considered.
Imaging of both the brain and the orbits should be performed. Orbital imaging provides details about the optic nerves and the surrounding tissues that often are not detected with brain imaging alone.
When pathology is localized to the orbit, either CT or MRI can provide useful information. Orbital fat provides excellent contrast with the other orbital components on CT and MRI, and both modalities give excellent anatomical localization (see Figs 2-1, 2-2, 2-5).
Table 2-4 Imaging Choice Based on Clinical Scenario
Figure 2-14 A 19-year-old man was referred for evaluation of double vision following a motor vehicle accident. Examination revealed difficulty with adduction of the left eye and a narrowing of the palpebral fissure on attempted abduction of the same eye. Coronal CT scan demonstrates an entrapped left medial rectus muscle (arrow).
(Courtesy of Steven A. Newman, MD.)
Direct coronal images are useful in most orbital disorders (Fig 2-14; see also Figs 2-1, 2-2). With MRI, direct coronal imaging is not a problem, but CT may require specific positioning (eg, neck extension) that may be difficult to achieve with elderly patients. MRI of the orbit should be done with fat-saturation techniques designed to eliminate the high-intensity T1 signal from fat (see Figs 2-7, 2-9D).
Luccichenti G, Giugni E, Péran P, et al. 3 Tesla is twice as sensitive as 1.5 Tesla magnetic resonance imaging in the assessment of diffuse axonal injury in traumatic brain injury patients. Funct Neurol. 2010;25(2):109–114.
Mafee MF, Rapoport M, Karimi A, Ansari SA, Shah J. Orbital and ocular imaging using 3- and 1.5-T MR imaging systems. Neuroimaging Clin N Am. 2005;15(1):1–21.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.