Orbital Trauma

Michael Rothman

The globe and orbit constitute a very small portion of the body; however, trauma to this region assumes critical importance due to the high value we place on vision. The evaluation of orbital trauma has progressed rapidly with the development and wide distribution of computer-assisted imaging. Plain radiography, angiography, computed tomography (CT}, and magnetic resonance imaging (MRI), may all be used in the evaluation of orbital trauma and the search for foreign bodies. Copyright © 1997 by W,B. Saunders Company

T HE ORBIT MAY be injured directly or indi- rectly, with both blunt and penetrating trauma

occurring with equal frequency. Soft tissue swelling often obscures direct clinical evaluation of the globe, limits ocular motion, and may limit clinical assess- ment of vision. Plain film evaluation of the orbit may accurately depict the presence of bony injury, as well as the presence of radiopaque and radiolu- cent foreign bodies. However, the lack of soft tissue detail limits its utility for treatment planning. CT shows both soft tissue and bony injury, and more clearly defines the location and orientation of displaced bony fragments, foreign bodies and air. MRI may be complementary to CT scanning in certain patients, particularly with injuries involving the globe or optic nerve, but is contraindicated in the presence of a metallic foreign body.

The presence of orbital emphysema or penetrat- ing trauma, enophthalmos/exophthalmos, palpable bony step-off, visual loss or extra-ocular muscle deficit on physical examination indicates the need for cross-sectional imaging evaluation. 1,2

TECHNIQUE

In many emergency rooms, plain film evaluation of the orbit remains the standard initial imaging modality. Standard plain film examination of the orbit includes anteroposterior or Caldwell, lateral, and Water's views of the face. Although supplemen- tary views may be obtained (eg, Rhese view of the optic foramen), subtle and complex fractures are best evaluated by CT scanning. The ability to obtain an adequate plain film examination of the orbit may be limited in the presence of concurrent trauma elsewhere, particularly cervical injuries.

Standard CT examination should include both axial and direct coronal imaging at slice thick- nesses of 3 mm or less, with images presented in both soft tissue and bone windows (preferably using bone algorithm reconstruction). Imaging may be obtained with either conventional axial or spiral/ helical modes. Helically acquired data may be retrospectively reconstructed in thinner sections (1

to 1.5 ram), allowing for improved coronal recon- structions when direct coronal imaging is not possible, or is limited by streak artifact from dental materials. Obfique sagittal reconstructions along the course of the optic nerve may also be useful in selected circum- stances. Three-dimensional presentation of data sets can be performed, allowing interactive review and display, although the effort and time required to do so may be prohibitive in an acute setting. Contrast admin- istration is not necessary.

The use of MRI in acute trauma has not been studied prospectively in large series. Injuries to the orbit may be well demonstrated on MR1, and it is useful in selected cases, once metal foreign bodies have been excluded. 3,4 Standard evaluation of the orbit may be performed with a standard head coil or with a dedicated surface coil, and should include both axial and coronal Tl-weighted sequences (see the article by Belden, same issue). Oblique sagittal sequences may be useful for evaluation of the optic nerve injuries, while T2-weighted sequences and post-contrast infusion fat-suppressed images delin- eate globe injuries well (see the article by Kubal, same issue). Dynamic evaluation of extra-ocular muscle function may be obtained in patients with entrapment syndrome with or without diplopia.

FOREIGN BODIES

Foreign bodies may be deposited into the orbital soft tissues as a consequence of penetrating injury, and must be localized prior to surgical debride- ment. X-rays in orthogonal planes may provide sufficient information, but CT shows smaller frag- ments and their relationship to the globe and optic nerve 5,6 (Fig 1). Wood is generally appreciated

From the Department of Radiology, University of Maryland Medical Systems, Baltimore, MD.

Address reprint requests to Michael Rothman, MD, Anna Gudelsky Magnetic Resonance Imaging Facility, University of Maryland Medical Systems 22 S Greene St, Baltimore, MD 21201.

Copyright © 1997 by W.B. Saunders Company 0887-2171/97/1806-000455. 00/0

Seminars in Ultrasound, CT, andMRI, Vo118, No 6 (December), 1997: pp 437-447 437

438 MICHAEL ROTHMAN

Fig 1. Metal foreign bodies sip shotgun injury and repair. (A) Lateral CT Scout film. Multiple metal projectiles overlie the face and orbits. Metal mesh fixes orbit floor (arrow). (B) Axial CT, bone window: 2 metal BBs in right orbit, mesh plate is elevated above orbit floor (arrow). C) Axial CT above level of (B), soft tissue window. Displacement of optic nerve by elevated mesh plate (arrow) (subsequently re-operated and repaired).

emergently as linear air density, whereas glass is usually hyperdense (Fig 2). Plastics vary in their composition and thus, in their CT appearance. 7 Metals are hyperdense, and may cause streak artifact. Plain films or CT may be used with confidence to exclude the presence of ocular metal- lic foreign bodies before MRI. MRI may also be used to localize non-metallic foreign bodies, s Re- tained foreign bodies may lead to infection and abscess formation.

ISOLATED ORBITAL FRACTURES

Blow-out Fractures

"Blow-out" fractures occur when direct blunt force is applied to the globe and orbit, with disrup- tion of an orbital wall and resultant decompression of orbital contents. 9 The inferior or medial wall is

most often damaged, with the superior and lateral walls less commonly involved, l° By definition, the orbital rim is intact ("pure" blow-out fracture) il (Fig 3, 4). Herniation of orbital fat and periorbita into the adjacent maxillary or ethmoid sinuses may occur, and is easily observed on both CT and MRI. These injuries may be associated with displacement of the rectus muscles or their connective tissue attachments and limitation of range of motion of the globe (entrapment syndrome). 1° Children have an increased incidence of "trap-door" fractures and resultant limitation of range of motion as compared with adults) 2 Contusion and laceration of the extraocular muscles may also produce a restriction of motion. Fractures may allow communication of air into the orbit, often with air-fluid levels demon- strated within adjacent paranasal sinuses (Fig 5).

ORBITAL TRAUMA 439

Fig 2. Wood foreign body. (A) Axial CT. Linear air density (arrow heads) represents wooden FB. (B) Axial CT, delayed f011ow-up. Linear increased density (arrow heads) represents fluid accumulating in interstices of wooden FB. Surrounding soft tissue indicates hematoma and inflammatory reaction. Note additional FB (arrow) poorly observed on (A).

Extension of the fracture plane to involve the rim ("impure" blow-out fracture) generally indicates a more severe traumatic injury. 1t Involvement of the superior rim is particularly significant, and is associated with a greater likelihood of associated cranial injuries, especially in children. 13 As chil- dren age and the paranasal sinuses pneumatize, the incidence of orbital floor fractures increases. 14

Blow-in Fractures

"Blow-in" fractures are a result of the applica- tion of blunt force near the orbit, with decompres- sion and displacement of fracture fragments into the orbit. Patients present with proptosis and restric-

tion of gaze more frequently than with blow-out fractures, and surgical intervention is necessary is all cases.15 As with blow-out fractures, involvement of the orbital rim separates pure and impure blow-in fractures. Superior fractures are associated with more severe cranial injuries, especially epidu- ral hematomas and frontal lobe contusions ~6 (Fig 6).

COMPLEX ORBITAL FRACTURES

Complex fractures of the midface/orbit are well- defined by CT, including zygomaticomaxillary com- plex fracture (ZMC) or "tripod" fractures (the zygomatic arch, orbit, maxillary sinus, and zygo- maticofrontal process), "NOE" (naso-orbital- ethmoid), Le Fort type 2 and 3 fractures (involve- ment of the pterygoid plates, nasal cavity, and orbit walls), and skull base fractures extending through the optic canal, MRI may be helpful acutely in directly evaluating the intracanalicular portion of the optic nerve. CT and MRI may also be helpful in the evaluation of chronic sequelae of orbital inju- ries, such as entrapment syndromes (Fig 7), exoph- thalmos/increased orbital volume (Fig 6), enophthal- mos/decreased orbital volume, visual disturbances/ diplopia, and post-surgical complications (Fig 1).

Zygomaticomaxillary Complex Fracture

ZMC fractures are usually the result of direct trauma to the malar eminence, resulting in depres- sion of the cheek, dental malocclusion, or trismus. Facial anesthesia due to trauma of the infraorbital nerve is common. The complex includes fractures of the zygomatic arch, orbit floor and rim, anterior, lateral and posterior walls of the maxillary sinus, and zygomaticofrontal process (Figs 8, 9). Nondis- placed fractures are termed "simple." "Complex" fractures are associated with more significant vascu- lar or airway injuries due to the medially displaced and rotated fracture fragments. ~7 Although plain films may delineate the fracture lines well, CT is

Fig 3. Concurrent inferior and medial blow-out fractures. (A, B, C, D) Plain film, Caldwell view; coronal CT, bone and soft tissue windows; coronal Tl-weighted MRI. Left orbit floor and medial wall are disrupted, with dependent soft tissue density representing herniated orbital contents (*), bone fragment (arrow), and partial opacification of maxillary sinus. Medial rectus muscle (arrow head) is tented toward the opacified left ethmoid air cells and medial blow-out fracture. Soft tissue streaky density within intraconal space represents hema- toma. (E,F) Axial CT and Tl-weighted MRI. Medial blow-out fracture and medial rectus tenting (arrow head) are better seen. Intraconal hematoma and left globe hemorrhage with choroidal detachment (large arrowhead) are also noted.

440 MICHAEL ROTHMAN

Fig 3 (on previous page).

ORBITAL TRAUMA 441

Fig 6. Superior blow-in fracture. Coronal T1-weighted MRI. Right superior orbit encephalocele (arrow), old, due to prior superior blow-in fracture.

Fig 4. Superior blow-out fracture. (A) Coronal CT, bone win- dow. Comminuted fracture of the orbital roof (arrow). CT of the brain shows a subfrontal hematoma and cortical contusion.

preferred for its ability to accurately define the degree of displacement of the fracture fragments.

Naso-Orbital-Ethmoid Complex Fracture

The NOE fracture occurs due to direct trauma to the midface and nasal bones. Concurrent complex bilateral facial trauma and multisystem injuries are commonly observed when the trauma is due to

high-speed motor vehicle accidents, but simple fractures are more frequent when the injury is due to a direct blow as from a fist.18 Fractures may include avulsion of the fossa, comminution of the fossa or canal, and linear fractures of the canaP 9 (Fig 10). Transection of the nasolacrimal apparatus may occur, but is infrequent. Telecanthus, or widen- ing of the interorbital distance, may be observed acutely and is due to avulsion of the medial canthal ligament. Epiphora or lacrimal mucocele due to blockage of the duct, and rhinorrhea secondary to cerebrospinal fluid leak from a concurrent cribi-

Fig 5. Medial blow-out fracture. (A,B) Axial and coronal CT, bone window. Extensive intra- and extra-conal orbital air from lamina papyrcea disruption/ethmoid sinus outlines intraorbital structures.

442 MICHAEL ROTHMAN

Fig 8. Zygomaticomaxillary complex fracture (ZMC). (A) Plain film, Water's view. Left ZMC fracture, including zygomatic arch (a), orbit floor and rim (b), anterior, lateral (c) and posterior walls of the maxillary sinus, and zygomaticofrontal process (d).

form plate or frontal sinus fracture, may occur in delayed presentation.

Le Fort Fractures

These midface fractures occur along lines of structural weakness, as defined by Le Fort in 1901. Three types are classically described (in order of increasing severity): (1) transverse fracture through the maxilla above the level of the hard palate including the pterygoid plates, resulting in dissocia- tion of the maxilla from the midface; (2) pyramidal fracture crossing the nasal bridge and septum, medial orbital walls and floors, maxillary antra, and pterygoid plates, resulting in dissociation of the midface from the cranium; (3) transverse fracture through the nasal bridge, and orbits, then diverging through the zygomaticofrontal processes and arches, and the maxilla and pterygoid plates, resulting in craniofacial dissociation (Fig 11). Although origi- nally described as bilaterally symmetrical, pure

c

Fig 7. Medial b low-out fracture, chronic. (A, B, C) Axial and coronal CT soft t issue window, coronal CT bone window. Tented and clinically entrapped left medial rectus muscle (arrow head), with herniation of medial rectus muscle, fat, and periorbita into ethmoid air cells, Lack of sinus fluid, and clinical history, confirm chronicity. Note persistent intraorbital air on coronal CT, indicating continuing communication of sinus cavity and orbit.

ORBITAL TRAUMA 443

Fig 9. Zygomaticomaxillary complex fracture. (A, B, C, D) Axial, coronal anterior, coronal posterior and 3D CT, bone win- dow. Right ZMC fracture, including zygomatic arch(a), orbit floor and rim (b), anterior, lateral and posterior walls of the maxillary sinus (c), and zygomaticofrontal process (d). This patient also has a right naso-orbital-ethmoid fracture (arrow).

fracture patterns are rare, and combinations of complex midface fractures are usually observed: the "facial smash" 17 (Figs 10, 12).

Complications due to this severe facial trauma are extremely common. Soft tissue hematomas resulting in airway compromise must be excluded during the evaluation process. Immediate and de- layed cerebrospinal fluid leaks occur more often with these injuries than with other orbitofacial fractures. Coexistent remote trauma is also frequent due to the high-velocity impact that produces these injuries) 7

TRAUMATIC CRANIAL NEUROPATHIES

Diplopia occurring in the setting of orbital trauma is common and may be due to either injury or restriction of the extraocular muscles or cranial nerves. Cranial nerve injury may occur at the brainstem, in the cisterns, at the skull base or cavernous sinus, or at the orbital apex. CT scanning in axial and coronal planes evaluates the extracra- nial and skull base segments effectively, but MRI, with high-resolution thin section sequences, best visualizes the intracranial extent of the cranial

444 MICHAEL ROTHMAN

Fig 10. Naso-orbital-ethmoid fracture/facial smash. (A, B) Axial CT inferior and superior levels. Comminuted, impacted bilateral facial fractures with displacement and rotation of nasolacrimal sac/lacrimal bone and duct (arrow). (C) Anteroposterior dacrocys- togram transecting and obstructing the nasolacrimal duct (arrow).

nerves. Cranial nerves 2, 3, 4, 5, and 6 (optic, ophthalmic, trochlear, trigeminal, and abducens) may all be injured following trauma.

Optic nerve injury may result from direct pene- trating trauma, or may be due to compression or transection in association with fractures of the orbital apex/optic canal? ° Loss of visual acuity or visual field deficits are noted by the patient or discovered on physical examination. The presence of post-septal soft tissue density in and around the optic nerve sheath is indicative of perineural hema- toma (Fig 13). Bony fragments may also displace or contuse the nerve (Fig 14).

Isolated ophthalmic nerve (CN 111) palsy due to

trauma is less common than CN III palsy from other causes? ~ Patients present with a combination of diplo- pia, ptosis, and pupillary dilation. The presence of neck pain, Homer's syndrome, or bruit on physical examina- tion should prompt further evaluation of the vascular tree for the possibility of internal carotid dissection.

Trochlear (CN IV) nerve palsy occurs secondary to trauma more often than from any other cause. CN IV innervates the superior oblique muscle, and its deficit results in unopposed action of the inferior oblique muscle. Identification of a trochlear deficit clinically is difficult as a palsy results in hypertro- pea, mimicking a blow-out fracture on physical examination. 2a

ORBITAL TRAUMA 445

Fig 11. Le Fort fracture. (A, B, C, D) Axial CT from inferior to superior, 3D reconstruction. Bilateral Le Fort fractures: right Le Fort I, II, Left Le Fort I, II, II1. Pterygoid plates fractures (large arrow head) define this complex.

Fig 12. Facial smash. (A, B) Axial CT bone and soft tissue windows. Bilateral facial smash-highly comminuted and impacted crush facial injury. Left globe is ruptured and filled wi th hemorrhage.

446

Trigeminal (CN VI) nerve palsy results in facial anesthesia and absent corneal reflex. It is com- monly injured in fractures of the orbit floor or roof, especially if the rim is involved. Fractures through the orbital apex/fissures may also produce Clinical symptoms. ~ 7

Abducens palsy (CN V1) is the most frequently encountered cranial neuropathy and results in lat-

M CHAEL ROTHMAN

Fig 13. Penetrating trauma, (A, B, C) Axial and coronal CT, sagittal reconstruction along the course of the optic nerve. Perineural hematoma (h) along optic nerve following stab injury to inferiomedial orbit with a pencil.

Fig 14. Optic canal fracture and optic nerve compression. (A, B) Axial and coronal CT, bone window, Complex skull base fracture-extending through right optic canal; with inferior displacement and clockwise rotation of the fracture fragment (arrow). Right sphenoid sinus Iocule is opacified, right ptery- gold plates are fractured (open arrows); right superior Orbit rim is fractured (arrowhead). ,

eral rectus palsy and limitation of lateral gaze. The ner+e's long intracranial course is thought to be responsible for its increased susceptibility to trau- matic injury. 23

Acute or delayed onset of post-traumatic dipl0- pia associated ~ith proptosi s and chemosis, sug- ge;ts a diagfiosis Of direct carotid cavernous fistula (CCF! (Fig. 15) '. Direct CCF results from a tear of the cavernous internal carotid artery that allows arterial blood [0 enter the cavernous sinus, revers- ing tl~e flo~v in the venous tributaries. Prominent anterior .venous drainage resultS in the Orbital presgntatidn. 24

ORBITAL TRAUMA 447

Fig 15. Traumatic direct carotid cavernous fistula. (A) Axial CT bone windows demonstrate fractures of the superior orbital fissure, lateral sphenoid wall, and carotid canal (arrows). Note the bilateral comminuted temporal bone fractures. (B) Lateral internal carotid arter!ogram demonstrates a direct carotid cavernous fistula with anterior venous drainage into the superior (SOV) and inferior (IOV) ophthalmic veins a s well as posterior drainage into the inferior (IPS) and superior (SPS) petrosal sinuses.

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