Magnetic resonance imaging based normative orbital measurements in an Australian population

Khizar Rana, Valerie Juniat, Sandy Patel, Dinesh Selva

Meeting:  2022 RANZCO


Date:      -

Session Title: FREE PAPERS – Oculoplastic/Ocular Oncology

Session Time:      -

Purpose: To determine the normal diameters of orbital structures on high resolution magnetic resonance imag- ing (MRI) sequences and correlate with patient demo- graphics in an Australian cohort.

Method: Retrospective review of patients who under- went 3T T1-weighted fat suppressed contrast enhanced MRI orbits. The maximum extraocular muscle and supe- rior ophthalmic vein (SOV) diameters on the normal orbits were recorded. Patients with bilateral disease or poor scan quality were excluded.

Results: A total of 213 orbits from 138 patients were included. The mean age of participants was 58 years (20-94 years) and 65 (47.1%) were male. Normal measure- ments (mean ± SD) were as follows: medial rectus 4.14± 0.52 mm; inferior rectus 4.63 ± 0.72 mm; lateral rectus (LR) 3.90 ± 0.69 mm; superior muscle group 4.49± 0.71 mm; superior oblique 3.03 ± 0.68 mm and the SOV 1.78 ± 0.68 mm. Males had significantly larger mean diameters of the LR (p < 0.01) and inferior rectus (p = 0.03). Significant correlation was found between age and medial rectus (r = -0.21, p < 0.05) and LR (r = 0.25, p < 0.01) diameters. Conclusion: Contrast enhanced MRI is the preferred imaging modality for evaluating pathological conditions affecting the orbit including infections, neoplasms and vascular malformations. This 3T-MRI data may help in diagnosing pathologic enlargement of the extraocular muscles and SOV on a contrast enhanced MRI sequence.