Facial trauma constitutes a public health problem. Due to anatomical proximity, craniofacial trauma involves orbital injury in up to 15%.It associated with significant morbidity, including permanent visual loss.
Clinical assessment may be limited by edema and concomitant injuries, therefore imaging has a primary role in delineating the trauma pattern and extent of injury.
Relevant anatomy
The orbit is a relatively small and anatomically complex space that contains many critical structures. An understanding of ocular anatomy is critical to appreciating how trauma can affect distinct parts of the orbit and globe.
The orbit is a pyramidal shaped space formed by seven bones. The orbital walls vary considerably in their thickness. The medial and inferior walls are particularly thin, thus explaining their proneness to fracture. Fig. 1
Its main function is to support and protect the eye, which lies anteriorly. Posterior to the globe is the six extraocular muscles and their intermuscular fascial membranes forming an intraorbital conical structure filled by orbital fat, Veins and lymphatics.
Centrally passes the optic nerve sheath which is a dural reflexion containing the ophthalmic artery, the optic nerve, and small veins.
Imaging Options :
Radiology plays a critical role in the diagnosis and treatment planning of traumatic orbital injuries.
Computed tomography (CT) is the primary modality for assessing acute orbital trauma because of its high sensitivity and spacial resolution.
The optimal protocol is a thin-sliced CT scan performed with a helical CT, demonstrating both soft tissues and bones with 3D reconstruction in both sagital and coronal reconstructions.
It can distinguish foreign bodies, gas, edema, hemorrhage, and bone fractures, as well as intracranial complications. Furthermore CT angiography can assess adjacent vascular injury.
The major concern with orbital CT is the radiation dose to the ocular lens which current-generation scanners are able to decrease.
Ultrasonography (US), is a robust modality for evaluating globe injury particularly if direct visualization is obscured by intraocular hemorrhage. It may be used to quickly locate an intraocular foreign body. However, US is contraindicated if a ruptured globe is suspected. Fig. 2
Using Magnetic resonance (MR) imaging for the initial evaluation of an orbital trauma is not recommended, it is even contraindicated if there is a possibility that a metallic intraorbital foreign body is present. Although it may be very useful if associated intracranial complications are suspected.