View 2019 Abstracts

MRI Orbits are frequently requested to assess optic nerve dysfunction in the context of orbital pathology. Radiologists currently use subjective assessments of optic nerve sheath diameter (ONSD) and optic nerve diameter (OND) to diagnose optic atrophy (OA). Do objective measurements and asymmetry of the OSND/OND ratio correlate with clinical signs of OA?

A retrospective study of MRI Orbits scans performed over 5 years in a tertiary centre. Data was collected from the Trust imaging system (PACS) and electronic medical records. ONSD and OND was measured by an ophthalmologist and neuroradiologist from coronal STIR or T2W scans.

ONSD and OND could be clearly measured in 100 of 129 scans reviewed. The most reliable point to measure was 3-5mm behind the globe. Asymmetry in the ONSD/OND ratio was noted in 31.6% (18/57) of patients with no clinical signs of OA but 62.8% (26/43) of patients with clinical signs of OA (p=0.08). However, there was statistically significant ONSD/OND asymmetry in patients with unilateral signs of clinical OA, with or without reported radiological signs of OA (p=0.04). Eyes with clinical signs of OA had a statistically significant increase in the ONSD/OND ratio compared to eyes with no signs of OA (p=0.009).

Objective measurements of the ONSD/OND ratio correlate with clinical signs of OA but are only reliable 3-5mm behind the globe. ONDS/OND asymmetry is present in normal subjects but it is more frequent in eyes with optic nerve dysfunction, particularly in unilateral disease.