Neuroimaging is an excellent diagnostic and prognostic tool in ophthalmology. However, it should be used in conjunction with, not as a substitute for, a detailed clinical evaluation of the patient. Prior to selecting an appropriate neuroimaging technique, the ophthalmologist should address the following clinical questions:
What is the clinical presentation?
Where is the lesion resulting in the clinical presentation?
What are the potential etiologies of the lesion?
The choice of imaging modality and the timing of the study should be based on the differential diagnosis, nature of the suspected lesion (eg, vascular), location of the lesion, patient characteristics (eg, age, weight, allergies, comorbidities such as renal function, claustrophobia, presence of metallic foreign bodies or devices such as a pacemaker), and the availability of the desired imaging modality. The ophthalmologist should communicate directly with the neuroradiologist when selecting the best imaging modality and interpreting the neuroimaging study. Errors that the clinician might make when either ordering or reviewing a neuroimaging study fall into 2 broad categories: (1) prescriptive and (2) descriptive. Prescriptive errors include the following:
failure to apply a dedicated study
inappropriate use of a dedicated study
omission of intravenous contrast material
omission of specialized sequences
Interpretive errors include the following:
failure to detect a lesion due to misleading clinical information
rejection of a clinical diagnosis because an expected imaging abnormality is absent
the assumption that a striking imaging abnormality accounts for the clinical abnormality
failure to consider the lack of clinical specificity of an imaging abnormality
This chapter primarily discusses the 2 most common neuroimaging techniques used in neuro-ophthalmology clinical practice: (1) computed tomography (CT) (Fig 2-1) and (2)magnetic resonance imaging (MRI) (Fig 2-2). In general, most neuro-ophthalmic diseases are best assessed with MRI of the brain and/or orbits using contrast and fat-saturation techniques. If a vascular abnormality is suspected, magnetic resonance angiography (MRA) or magnetic resonance venography (MRV) can be added to the MRI; computed tomography angiography (CTA) or computed tomography venography (CTV) can be added to the CT.
Figure 2-1 Computed tomography (CT) scans. Axial (A) and coronal (B) orbital views of a healthy subject.
(Courtesy of Rod Foroozan, MD.)
Figure 2-2 Brain and orbital magnetic resonance imaging (MRI) scans showing anatomical visual and orbital structures from the chiasm to the anterior orbit. (The abnormality of the left globe is not pertinent to the objective of this figure.) T1-weighted axial (A), T1-weighted coronal (B–D), T2-weighted coronal with fat saturation (E), and T1-weighted coronal (F) images. ACF = anterior cranial fossa; Ant segment = anterior segment; ICA = internal carotid artery; IO = inferior oblique muscle; IR = inferior rectus muscle; LR = lateral rectus muscle; Lev P = levator palpebrae superioris muscle; MCF = middle cranial fossa; MR = medial rectus muscle; Olf fossa = olfactory fossa; SO = superior oblique muscle; Sph sinus = sphenoid sinus; Sph wing = sphenoid wing; SR = superior rectus muscle; Temp lobe = temporal lobe; Vit = vitreous.
(Courtesy of M. Tariq Bhatti, MD.)
The use of plain (x-ray) film in the evaluation of neuro-ophthalmic diseases has largely become obsolete, except to evaluate for a metallic foreign body. A glossary of select neuroimaging terminology appears at the end of this chapter.
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Custer PL, Kent TL. Pitfalls of ophthalmic radiographic imaging. Curr Opin Ophthalmol. 2014;25(5):432–435.
Lee AG, Johnson MC, Policeni BA, Smoker WR. Imaging for neuro-ophthalmic and orbital disease—a review. Clin Exp Ophthalmol. 2009;37(1):30–53.
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.