MRI Brain Without and With Contrast for Monocular Vision Loss
For a patient with acute monocular vision loss concerning for possible stroke, obtain an MRI brain without and with contrast, which should include diffusion-weighted imaging (DWI) sequences. This is the preferred imaging modality over CT and should be performed within 24 hours of symptom onset.
Primary Imaging Recommendation
MRI brain without contrast with DWI sequences is the preferred initial brain imaging modality for patients presenting with suspected vascular monocular vision loss, as it is far more sensitive than CT for detecting acute ischemic stroke 1, 2.
Adding contrast (MRI brain without and with contrast) is recommended when evaluating monocular vision loss with suspected vascular etiology, as it provides superior evaluation of the optic nerve pathology, orbital structures, and can identify mass lesions or inflammatory processes that may mimic stroke 1.
The ACR Appropriateness Criteria specifically recommend MRI of the orbits without and with contrast as the preferred modality for evaluating monocular visual loss involving the optic nerve or pre-chiasm structures 1.
Critical Timing and Detection Capabilities
Brain MRI should be performed within 24 hours of symptom onset in patients with suspected vascular monocular vision loss 1.
MRI with DWI detected acute ischemic stroke in 46% of patients scanned within 3 hours of symptom onset, compared to only 7% detection by CT 2.
In patients with monocular vision loss of vascular etiology (including transient monocular vision loss, central retinal artery occlusion, or branch retinal artery occlusion), up to 19.5% have concurrent acute ischemic stroke on DWI-MRI even without other neurologic deficits 3.
CT scans failed to identify the majority of acute stroke lesions that were detected by DWI-MRI in patients with monocular vision loss 3.
Why Contrast Should Be Added
Contrast enhancement is essential because monocular vision loss can result from multiple etiologies beyond stroke, including:
Without contrast, you may miss critical diagnoses such as demyelinating plaques, small tumors, areas of infection or inflammation, or vascular malformations that could produce stroke-like symptoms 1.
Complete Vascular Imaging Protocol
Beyond the brain MRI, noninvasive imaging of the cervicocephalic vessels should be performed routinely as part of the evaluation 1:
- MRA (magnetic resonance angiography) is preferred and can be obtained simultaneously with the brain MRI 1.
- MRA without and with contrast may be preferred over CTA if time-resolved information is needed for lesion characterization 1.
- Vascular imaging can detect stenotic lesions, intracranial stenoses, aneurysms, vasculitis, and dissections that might alter acute care and secondary prevention 1.
Common Pitfalls to Avoid
Do not rely on CT alone: CT has poor sensitivity for acute ischemic stroke in the hyperacute setting (only 10% detection rate vs 46% for MRI) and will miss the majority of strokes in patients with monocular vision loss 2, 3.
Do not skip contrast unless contraindicated: While MRI without contrast can detect acute stroke, adding contrast is critical for comprehensive evaluation of the multiple potential etiologies of monocular vision loss 1.
Do not delay imaging: The 24-hour window is important for optimal stroke detection and management decisions 1.
Do not assume absence of other neurologic deficits rules out stroke: Nearly 1 in 5 patients with isolated monocular vision loss of vascular etiology have concurrent acute stroke 3.