Isotropic proton-density-weighted high-resolution MRI for volume measurement of reconstructed orbital fractures - a comparison with multislice CT

Objective: The cause of enophthalmos as a late complication after orbital reconstruction is poorly investigated. Multislice CT (MSCT) is usually employed for its assessment, in spite of limitations regarding soft tissue depiction/imaging, as well as the implication of radiation and production of artifacts. Magnetic resonance imaging (MRI) has been shown to be a valuable alternative. The aim of this study was to establish a bony and soft tissue orbital volume calculation method based on different high-resolution MRI sequences compared to MSCT. Materials and Methods: Thirty-seven patients were included in this prospective study investigating the origin of enophthalmos present 3-4 months after complex orbital reconstruction. Morphological and dimensional changes of the orbit, eye globes, extraocular muscles and fat content were investigated 3-4 months after surgery. To assess the site and size of bony and soft tissue changes in the traumatized orbits, we used MSCT and MR images as well as corresponding 3-D reconstructions. Results: All enophthalmic orbits revealed a significant bony volume increase compared to the contralateral side as well as a reduced sagittal eye projection. Mean orbital volume enlargements of 1.0 cm³ lead to 0.93 mm enophthalmos (P<.05). Hardly any fatty atrophy could be depicted by the different MRI techniques. Conclusions: For soft tissue depiction of the orbit, MRI was superior to MSCT. Particularly, proton density weighting proved to be the best sequence for soft tissue volume segmentation, allowing determination of the cause and degree of posttraumatic enophthalmos in reconstructed orbits.