MRI Signal Intensity Varies Along the Course of the Normal Optic Nerve.

Area of Science:

• Neuroimaging
• Ophthalmology
• Neurology

Background:

• Magnetic Resonance Imaging (MRI) aids in differentiating optic neuropathy causes, including optic neuritis.
• Neuromyelitis optica spectrum disorder (NMOSD) characteristically enhances prechiasmatic optic nerves.
• Understanding normal optic nerve MRI signal is vital for accurate diagnosis.

Purpose of the Study:

• To investigate intensity differences between the prechiasmatic optic nerve (PC-ON) and midorbital optic nerve (MO-ON) on MRI in patients without optic neuropathy.
• To establish a baseline for normal optic nerve signal intensity in MRI.

Main Methods:

• Retrospective analysis of 75 patients undergoing brain MRI for ocular motor nerve palsy.
• Inclusion criteria: age ≥18, visual acuity ≥20/25, no optic neuropathy evidence.
• Quantitative intensity measurements of PC-ON and MO-ON on pre/postcontrast T1 axial images, normalized using temporalis muscle intensity.

Main Results:

• The PC-ON demonstrated significantly higher intensity ratios than the MO-ON on both precontrast (19.6%) and postcontrast (14.2%) T1 images (P < 0.01).
• No significant effect of age, gender, or laterality on these intensity measurements was observed.

Conclusions:

• Normal prechiasmatic optic nerves exhibit higher MRI signal intensity compared to midorbital optic nerves.
• This subtle intensity difference on T1-weighted MRI is important for clinicians to recognize when evaluating suspected optic neuropathy.