Page 31 - Advanced concepts in orbital wall fractures
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                                Introduction
Reconstruction of the bony orbit is a challenge in posttraumatic orbital
wall reconstruction, as well as in the treatment of orbital pathologies C such as decompression surgery in Graves’ orbitopathy. The orbit has 2 a complex conical structure1,2. A blow-out fracture is usually the result
of trauma to the globe and causes an increase in volume of the bony
orbit. An increase of >2 cc can lead to significant functional and aesthetic
sequelae such as diplopia and enophthalmos3,4. Both diplopia and enophthalmos are also seen as a complication after reconstruction of
orbital fractures, possibly due to suboptimal anatomical repositioning or reconstruction. An increase of 1 cc in orbital volume is believed to result
in 1 mm of enophthalmos on average1,5-9. Other recognized causes of
merely late enophthalmos are fat atrophy, fibrosis, and loss of periorbital
support10. Regardless of the approach or choice of materials, restoration
of orbital volume to improve function and aesthetics should be the main
goal11. An accurate preoperative assessment of the orbital content is of
importance for achieving an anatomically perfect end result12. Orbital
volume measurement is a useful addition to preoperative planning for
orbital reconstruction, e.g., in traumatology, pathology, or decompression
surgery.
Computed tomography (CT) is the imaging modality of choice in orbital wall fractures13-17. The quality of CT scanners and reconstruction software has improved significantly over the years. This has enabled the clinician to assess the bony orbit more precise. Despite these improvements, it is still difficult to determine the volume of the bony orbit. The orbital medial wall and orbital floor are very thin structures and their boundaries are not well defined. This is partly due to the partial volume effect18,19. The position of the anterior boundary is arguable and the posterior boundary is complex with its annulus, inferior and superior orbital fissure, and optic foramen.
Several methods to measure orbital volume have been validated over the years20. Manual segmentation, outlining the content of the bony orbit slice by slice, is accurate. Unfortunately, it is time-consuming and poorly applicable in clinical practice. In the past, software programs have been
Volume segmentation method
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