Computed Tomography-based Measurement of Herniated Orbital Volume Following Acute Orbital Fractures

To predict which patients will develop more than 2 mm of enophthalmos and require surgery after orbital fracture is challenging. Although high herniated orbital volume (HV) might be a predictor, its measurement can be complex and time-consuming. This study aimed to identify a simple, reliable, and clinically applicable method for measuring herniated orbital volume.

This single-center retrospective study examined HV and approximate volume in 42 patients with an orbital floor fracture (OF group) and 56 patients with a medial wall fracture (MW group). Approximate herniated volume (AV) was calculated as a rectangular parallelepiped, quadrangular pyramid, or hemiellipsoid. The correlation between HV and AV was analyzed quantitatively. Receiver operating characteristic curve analysis was performed to compare AV and HV cutoff values.

AV calculated as a hemiellipsoid (AVhe) provided the closest approximation to HV. Correlation analysis showed a positive linear relationship between HV and AVhe in both the OF group (r = 0.818) and the MW group (r = 0.84). The optimal AVhe cutoff value was 1.013 mL in the OF group (positive and negative predictive values, 96.3% and 66.7%, respectively; area under the curve, 0.925) and 1.13 mL in the MW group (positive and negative predictive values, 90.0% and 69.2%, respectively; area under the curve, 0.956). High HV was defined as greater than 1.0 mL in the OF group and greater than 0.9 mL in the MW group.

A simplified method that approximately calculates the volume of herniated orbital contents in a hemiellipsoid pattern model proved to be practical, easy, and reliable.