Validation of exophthalmos magnetic resonance imaging measurements in patients with Graves’ orbitopathy, compared to ophthalmometry results

Purpose
Although assessment of the orbital structures using magnetic resonance imaging (MRI) is well described in the literature, there is no consensus as to which measurement method is the most useful in exophthalmos assessment. The aim of the study was to correlate 2 MRI methods of exophthalmos measurement with exophthalmometry results and to determine a proper technique of exophthalmos measurement.

Material and methods
Fifty-four patients (108 orbits) with exophthalmos in the course of Graves’ orbitopathy were enrolled in the study. Two measurements on axial T2W orbital MRI images were performed by 2 independent radiologists: the distance from the interzygomatic line to the anterior surface of the globe (AD) and the distance from the interzygomatic line to the posterior sclera (PD). Within 4 weeks, an exophthalmometry was performed by an ophthalmologist using a Hertel exophthalmometer. The inter-observer variation was assessed using the Pearson correlation coefficient. Values were presented as mean and standard deviation, and the differences in values were explored with Student’s t-test.

Results
The mean AD measured on MRI by the first observer was 20.6 ± 3 mm, and 20.6 ± 2.9 mm by the second observer. PD values were 2.9 ± 2.8 mm and 3.4 ± 2.8 mm, respectively. The mean exophthalmometry result was 21 ± 3.3 mm. The correlation was very high between observers for AD measurements (r = 0.98, p = 0.01) and high for PD measurements (r = 0.95, p = 0.01). AD measurements on MRI and exophthalmometry results were strongly correlated (r = 0.9, p = 0.01).

Conclusions
The AD measurement has better reproducibility and is directly correlated with Hertel exophthalmometry. This method could be sufficient in routine practice.