Pediatric emergency medicine trisk 824

Knowledge of the bony anatomy of the orbit is integral to the understanding of
fractures at this site. The superior portion of the orbit is composed of the superior
orbital rim and orbital roof, which is part of the thick frontal bone. The medial
wall is formed by the ethmoid bone, which is adjacent to the nasal bones. The
lateral wall is formed by the greater wing of the sphenoid and the zygoma, which
are also quite thick. The floor and the inferior orbital rim are formed by the
zygoma and the maxilla, which are relatively thin, and are further weakened by
the groove for the infraorbital nerve.
Fractures of the floor of the orbit, sometimes known as “orbital blowout
fractures,” typically occur when a medium-sized, round, hard object, such as a
baseball, strikes the eye ( Fig. 107.3 ). The volume of the globe is fixed; thus,
when an acute increase in orbital space (an opening in the floor of the orbit)
occurs, the globe may be pushed posteriorly in the orbit, producing
enophthalmos, a sunken appearance to the eye. A true orbital blowout fracture
denotes a fracture of the floor of the orbit, with an intact inferior orbital rim.
Although these fractures are quite rare in children, they are often due to direct
trauma to the zygoma rather than a compression of the globe itself. Blood and
orbital fat may sink into the maxillary sinus, clouding the sinus on radiograph (
Fig. 107.4 ). Asymmetry in the horizontal level of the eyes (orbital dystopia) may
also be present. The infraorbital nerve, the terminal branch of the maxillary
division of the trigeminal nerve, exits the maxilla just below the infraorbital rim.
Manifestations of injury to this nerve include decreased sensation to the cheek,
upper lip, and upper gingiva on the affected side. Nausea and vomiting are often
present with orbital blowout fractures and may be mistaken as symptoms of head
injury.


FIGURE 107.3 Mechanism of blowout fracture. In a sagittal view, a ball is shown striking the
eye, deforming it, and causing increased pressure of the intraorbital contents. The periorbital fat
is forced through the floor of the orbit. Retropositioning of the eye (enophthalmos), lowering of
the eye, and extraocular muscle entrapment can result.

In children, the floor of the orbit is relatively flexible. Consequently, it may
fracture in a linear pattern that snaps back to create a “trapdoor” fracture. In
adults, the floor of the orbit is thick and more likely to shatter when exposed to
force. If the inferior rectus muscle is entrapped in the fracture gap in the floor of
the orbit, voluntary upward gaze may be limited. Thin-cut coronal CT is
especially valuable in detection of orbital blowout fractures and extraocular
muscle entrapment. The presence of entrapment is an indication to operate on a
blowout fracture on an urgent basis.
A thorough ophthalmologic examination is warranted in all patients with
orbital fractures because of the high likelihood of associated eye injuries. In
particular, vision should be assessed because decreased visual acuity may be an
early sign of a retrobulbar hemorrhage, or injury to the optic nerve or eye itself. A
retrobulbar hemorrhage can cause compression of the central retinal artery, which
can threaten vision to the affected eye if not surgically decompressed. The type of
eye and orbit injuries varies on the basis of the object and mechanism involved.
Typically, a low-impact mechanism with a small object will result in injuries to


the eye itself, such as a corneal abrasion or hyphema. Injury to the eye from a
high-speed soft object such as a tennis ball will often result in a hyphema. Hard
objects striking the orbit at a high speed, such as a baseball or a fist, are likely to
result in an orbital blowout fracture. High-impact mechanisms, such as those
encountered when the face strikes the dashboard in a motor vehicle collision, are
likely to result in complex orbital and midface fractures.


FIGURE 107.4 A: Blowout fracture. The sinus view shows teardrop configuration of the
blowout fracture in the right orbit. Note associated fracture through the orbital floor and air–
fluid level in the maxillary sinus. B: In the same patient as (A ), computed tomography section

more clearly demonstrates the multiple fragment fracture through the orbital floor. Teardrop and
air–fluid level are evident in the right maxillary sinus. (Courtesy of Soroosh Mahboubi, MD.)