Measurement of orbital volumes following trauma using low-dose computed tomography

Abstract

We describe a simple CT technique for the assessment of enophthalmos and measurement of orbital volumes following trauma. The technique uses original diagnostic CT images, standard CT software and involves no additional radiation dose or scan time. The results of this technique in 66 patients with orbital trauma are presented. The incidence of post-traumatic enophthalmos was significantly raised in association with combined blow-out fractures of the floor and medial wall of the orbit and where orbital blow-out fractures occurred in conjunction with zygomatic injury. Patients without bony imjury had a traumatised orbit volume less than 1 cm3 greater than the non-traumatised side in all cases. Intra-observer reproducibility of the measurement of difference in volume between traumatised and non-traumatised orbit was ± 0.3 cm3 (1 SD). In patients with fracture, increase in orbital volume by more than 2 cm3 compared with the contralateral orbit was strongly associated with enophthalmos (sensitivity 100%, positive predictive value 69%). We conclude that routine volumetric assessment following orbital trauma provides a clinically useful, objective assessment of the risk of post-traumatic enophthalmos and that an increase in orbital volume greater than 2 cm3 is an indication for surgical repair.