What is the next step in management for a patient with visual changes and a normal computed tomography (CT) scan?

MRI of the Brain with Contrast is the Next Step for Visual Changes with Normal CT Scan

For patients with visual changes and a normal CT scan, MRI of the brain with contrast is the recommended next step in management to identify potential pathology not detected by CT. 1

Rationale for MRI After Normal CT

CT scans have significant limitations in detecting many conditions that can cause visual disturbances:

• MRI provides superior soft-tissue resolution and is more sensitive than CT for detecting most neurological pathologies 1, 2
• MRI reveals clinically relevant additional abnormalities over CT in up to 95% of patients with neurological symptoms 2
• CT can miss subtle lesions affecting the visual pathways, particularly in the posterior fossa, brainstem, and optic pathways 1

Specific MRI Protocol Recommendations

The type of MRI study depends on the pattern of visual loss:

For Pre-Chiasmatic Visual Loss (Monocular):

• MRI of the orbits without and with contrast is preferred 1
• Focus on evaluating the globe, optic nerve, and orbital structures
• High-resolution sequences to visualize the optic nerve

For Chiasmatic or Post-Chiasmatic Visual Loss (Binocular):

• MRI of the brain without and with contrast 1
• Include thin-slice sequences through the pituitary and suprasellar region for bitemporal defects 1
• For homonymous defects, focus on post-chiasmatic visual pathways 1

Clinical Patterns and Imaging Focus

Different visual field defects suggest different anatomical locations requiring specific imaging focus:

• Bitemporal hemianopia: Suggests chiasmatic lesion - MRI brain with thin-slice pituitary protocol 1
• Homonymous hemianopia: Suggests post-chiasmatic lesion - MRI brain focusing on occipital and temporal lobes 1
• Monocular visual loss: Suggests pre-chiasmatic lesion - MRI orbits with contrast 1

Conditions Detected by MRI but Missed by CT

MRI is particularly valuable for detecting:

• Demyelinating diseases (multiple sclerosis, neuromyelitis optica) 1, 3
• Small ischemic lesions 2, 4
• Posterior fossa lesions 1
• Optic neuritis 1
• Brain tumors, especially low-grade gliomas 5
• Subtle vascular malformations 1

Special Considerations

• If optic neuritis is suspected, both MRI of the orbits and brain with contrast are recommended to evaluate for demyelinating disease 1
• If contrast cannot be administered, non-contrast MRI still provides valuable information but with reduced sensitivity 1
• In acute settings where stroke is suspected, MRI with diffusion-weighted imaging is particularly valuable 4

Common Pitfalls to Avoid

• Stopping at normal CT: A normal CT does not exclude pathology affecting vision 6, 2
• Incorrect MRI protocol: Using standard brain protocols without specific sequences for visual pathways may miss subtle lesions 1
• Ignoring clinical pattern: The pattern of visual field loss should guide the specific MRI protocol 1
• Overlooking non-structural causes: Some visual changes may be due to metabolic, toxic, or functional causes not visible on imaging 1

MRI is the definitive next step after a normal CT scan in a patient with visual changes, as it provides significantly higher sensitivity for detecting pathology that can affect the visual pathways throughout the brain.