Normative Measurements of the Infraorbital Nerve by Magnetic Resonance Imaging in an Australia Cohort.

Purpose: To report the normative dimensions of the infraorbital nerve on fat-suppressed gadolinium-enhanced MRI and correlate with patient demographics in an Australian cohort.

Methods: A retrospective review of patients who underwent coronal fat-suppressed gadolinium T1-weighted MRI from September 2021 to December 2023. One hundred sixty-eight orbits were included. The maximum diameter of the infraorbital nerve and the optic nerve sheath was measured. Orbits were excluded if there was unilateral or bilateral pathology of the infraorbital nerve or optic nerve sheath, incomplete MRI sequences, poor image quality, or indiscernible infraorbital nerve on radiological examination.

Results: The mean age of participants was 58 ± 16 years, and 50% were females (n = 42). The mean normative measurements (mean ± standard deviation) on coronal T1-weighted imaging: optic nerve sheath, 5.08 ± 0.67 mm. On coronal fat-suppressed gadolinium T1-weighted imaging: infraorbital nerve, 0.89 ± 0.22mm. No significant differences were found between male or female participants in both the infraorbital nerve (p = 0.757) or optic nerve sheath (p = 0.646). There was no significant correlation between age and mean diameter of the infraorbital nerve (r = 0.077, p = 0.320) or optic nerve sheath (r = 0.075, p = 0.336). Additionally, no significant difference was identified between the mean diameter of the infraorbital nerve (p = 0.079) and optic nerve sheath (p = 0.120) across age groups. The mean infraorbital nerve to optic nerve sheath ratio was 0.18 ± 0.00.

Conclusion: Normative dimensions of the infraorbital nerve may be used to identify enlargement in conditions such as IgG4-related ophthalmic disease and reactive lymphoid hyperplasia.