Optic nerve sheath imaging evaluates the coverings around the optic nerve within the orbit to assess conditions affecting intracranial pressure or local pathology. The subarachnoid space here is continuous with that around the brain.
Methods
Ultrasound, CT, and MRI can all measure optic nerve sheath diameter, with ultrasound often used at the bedside. High-resolution orbital MRI provides detailed views of the nerve, sheath, and surrounding tissues.
- Increased sheath diameter may reflect raised intracranial pressure
- Imaging can show sheath meningiomas or inflammatory thickening
- Standardised measurement points improve reproducibility
- Non-invasive ultrasound is particularly useful in acute settings
Clinical Role
Optic nerve sheath imaging assists in diagnosing idiopathic intracranial hypertension, papilloedema, and compressive lesions. It can also monitor treatment response.
- Useful when lumbar puncture or full neuroimaging is not immediately available
- Helps differentiate true disc swelling from pseudo-papilloedema
- Serial measurements may track changes in intracranial pressure
- Results must be considered with clinical findings and other investigations
