Applied Radiology

Dr. Bacelar is a Staff Radiologist in the Departamento de Radiologia, Instituto Português de Oncologia, Porto, Portugal. Dr. Rao is a Professor and the Chairman of the Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA.

Approximately 2% of all hospital admissions in the United States are due to facial fractures. Morbidity results when initial diagnosis and management are inaccurate, delayed, or suboptimal. ¹

High-resolution CT imaging has replaced conventional radiography for the evaluation of facial trauma because of its widespread availability and fast imaging capability. CT can also be performed with less potentially hazardous positioning of injured patients. Pre-sently, the necessity of a preliminary 4-film screening series of radiographs is questioned. A single 30š occipitomental radiograph can determine accurately which patients should have CT scanning. ² Axial and coronal CT scans at ¾ 3 mm slice thickness are essential for complete evaluation of the facial structures. Direct coronal CT scanning is preferred, but if not feasible due to cervical injury, thin-section axial helical scans should be performed that allow for reformations in the coronal plane with optimal resolution.

A recent study undertaken in cadaver heads showed high sensitivity and specificity for identifying clinically significant fractures on reformatted images in trauma patients. The authors suggested reformatted coronal images may be able to replace dedicated direct coronal maxillofacial scanning that are precluded in many patients due to suspected or associated cervical spine injury. ³

Three-dimensional (3D) CT imaging is useful as an adjunct to high-resolution thin-section CT and allows clinicians to visualize the fracture fragments and their relationship to one another. Three-dimensional images have been shown to add significantly in the evaluation of severe facial trauma in 29% of patients. ⁴ These images appear superior in localization of complex fractures involving multiple planes, ^5,6 in the evaluation of fracture displacement, and in the assessment of facial symmetry. ⁷ Also, 3D imaging is essential for fabrication of bone grafts used in complex facial restorations. ⁸ However, this does not supplant two-dimensional (2D) imaging for detection of fractures, especially for the deeper facial structures. The role of MRI in the evaluation of facial trauma is limited but may provide complementary information in special circumstances, such as associated traumatic aneurysms, carotid cavernous sinus fistula, etc.

Nasal fractures

Isolated fractures of the nasal pyramid represent approximately 50% of facial fractures. ^9,10 The majority of nasal bone fractures involve the thinner distal third of the nasal bones, and the nasal ethmoid complex remains intact. ^9,11 Nasal injuries may occur as isolated fractures or in conjunction with other facial injuries.

The naso-orbital-ethmoid (NOE) fracture involves the nasal bones, as well as the ethmoid sinuses and orbital rim. The anterior nasal structures are usually displaced posteriorly into the lacrimal bones and ethmoid sinuses. Changes in orbital volume with consequent injury to the medial canthal ligament, cribriform plates, nasofrontal duct, and nasolacrimal duct represent possible complications. ^10,12

Orbital fractures

Orbital fractures may be isolated or occur as a component of more complex mid-face fractures, including the tripod fracture, the Le Fort II and the Le Fort III fractures. Isolated orbital fractures may involve one or more of the following: floor, the lamina papyracea, roof, or lateral wall.

Orbital floor fracture (inferior blowout) (Figure 1) results from a direct blow to the orbit by an object that is too large to enter the orbit (ie, fist, baseball, etc.). The force of the blow is absorbed by the orbital rim and is transmitted to the thinner orbital floor, which usually fractures in the middle third near the infraorbital canal. Furthermore, as the eye is pushed back, the intraorbital pressure increases and this pushes the fracture fragments down into the maxillary sinus. Usually, the orbital rim and globe remain intact. These represent 3% to 5% of all mid-face fractures. ^13,14 Herniation of orbital fat, inferior rectus muscle, or the inferior oblique muscle can occur with muscle entrapment, resulting in diplopia.

On CT, entrapment may be seen as an abrupt kink in the muscle as opposed to a smooth prolapse through the site of fracture. ¹ Traumatic subluxation of the globe into the maxillary sinus has also been reported. ¹⁵ Orbital blowout fracture, where the fracture fragments show near complete realignment, are called trap door fractures (Figure 2). These are rather subtle and may be missed easily. There is a fine fibrovascular network that binds the tendon sheath of the inferior rectus muscle to the orbital floor periosteum and is prone to disruption resulting in limitation of ocular motility due to ischemic necrosis of the muscle. Failure to detect these fractures early precludes surgical intervention and results in poor clinical outcome. ¹⁶

Fracture of the lamina papyracea (medial blowout) (Figure 3) may occur either as an isolated fracture or in conjunction with an orbital floor fracture. Since these different types of fractures imply different surgical approaches, a classification based on location and severity of injury has been proposed. ¹⁷ The mechanism of injury is similar to that of the inferior blowout fracture. A medial blowout fracture may be present in as many as 50% of patients with orbital floor fractures. ¹⁸ Orbital emphysema, resulting from the ethmoid sinus fracture, occurs commonly in patients with medial blowout. ¹⁸ Herniation of orbital fat and entrapment of medial rectus muscle may occur. Indications for immediate surgery include definite muscle entrapment and acute enophthalmos. Orbital soft-tissue injuries include extraocular muscle entrapment, orbital hematoma, rupture of the globe (Figure 4), dislocation of the lens (Figure 5), retinal or choroidal detachment, and optic nerve injury.

The blow-in fractures involve the orbital roof with inferior displacement of fracture fragments into the soft tissues of the orbit. In more than half of such cases, it is associated with frontal sinus or skull fractures. ¹⁹ It has been reported that 14% to 29% of patients with blow-in fractures show ocular injuries. ²⁰

Zygomatic maxillary complex fractures (ZMC)

These are the second most common facial fractures. ¹⁸ Fracture lines extend in three directions, resulting in separation of the zygoma from the orbit, maxilla, and the temporal bone (Figure 6). Three components of the fracture include: 1) fracture of the lateral orbital wall extending through the zygomaticofrontal suture and the zygomaticosphenoid suture; 2) fracture of the anterior lateral walls of maxillary sinus extending through the zygomaticomaxillary suture; and 3) fracture through the zygomatic arch dorsal to or through the zygomaticotemporal suture. The infraorbital nerve is impaired in 94.2% of the cases. ⁹ In a simple ZMC injury, there is separation of the zygoma without angulation, while a complex or ZMC fracture reveals rotation and/or depression of the zygoma.

Zygomatic arch fracture

Depressed fracture of the zygomatic arch may be seen as an isolated fracture. It usually shows two distinct fracture fragments that are displaced medially and inferiorly. The fracture fragments may impinge on the temporalis muscle or coronoid process of the mandible and in some cases may alter dental occlusion.

Mid-face fractures (Le Fort classification)

Mid-face fractures are traditionally classified as Le Fort I, II, and III types according to the portions of the midface involved (Figure 7). ^12,21 By definition, these fractures are bilateral and symmetrical, and include extension through the pterygoid plates. Malocclusion of the maxilla and mandible is found almost universally. ^1,22

Le Fort I fractures result from a direct blow to the upper jaw region and are characterized by detachment of the upper jaw with tooth-bearing segment at a level just above the floor of the nasal cavity. The fracture lines extend through the lower nasal septum, the lower aspect of the maxillary sinuses, and the lower pterygoid plates. The constellation of fractures results in a floating palate.

Le Fort II fractures (pyramidal fracture) result from a direct forceful blow to the central facial region. This results in posterior displacement of the central mid-face. Fractures extend through the nasion, separating the nose from the cranium. The fracture lines extend on each side to involve the lacrimal bone, medial orbital wall, orbital rim, orbital floor, anterior lateral maxillary walls, and pterygoid plates in a pyramidal fashion. The zygomatic arches remain intact.

Le Fort III fractures (craniofacial dysjunction) result in complete separation of the facial skeleton from the skull base. The fracture lines extend through the nasal ethmoid complex and extend horizontally through the lacrimal bones, medial orbital wall, and separate the frontozygomatic suture. These fractures extend across the floor of the orbit to the inferior orbital fissure and the pterygoid plates. The zygomatic arches are also fractured. These patients are prone to complications such as cerebrospinal fluid (CSF) rhinorrhea, hemorrhage, injury to the inferior orbital nerve, and malocclusion. It is not unusual to find a combination of Le Fort II and III fractures in the same patient. Le Fort III fractures represent an extension of Le Fort II, and include fractures extending through the zygomatic arch and the frontozygomatic suture.

Mandibular fractures

The mandible is frequently fractured in association with severe midfacial injuries, particularly those of the LeFort variety. The mandible is fractured in more than one place 50% to 60% of the time. ²³ The condylar fracture (Figure 8) is the most frequently undiagnosed facial fracture, ²⁴ but is seen readily by coronal CT. ²⁵

Frontal sinus fractures

Frontal sinus fractures may occur in isolation, or in conjunction with mid-face fractures or cranial fractures. In the vast majority of patients, fractures extend only through the anterior table. Involvement of both the anterior and posterior tables may be seen in 25% of the fractures (Figure 9). ²⁶ Complications of fractures involving the posterior frontal sinus wall include CSF leak, meningitis, pneumocephalus, etc. When facial CT is performed for trauma, the absence of free fluid in a sinus cavity virtually excludes a fracture of the sinus walls. ²⁷

Temporal bone fractures

Temporal bone fractures are seen in 6% to 8% of patients with severe head trauma. ²⁸ Up to 30% of temporal bone fractures can be bilateral. ²⁸ Typically, these fractures are described as longitudinal, transverse, and mixed. The longitudinal fractures run along the long axis of the petrous bone and account for approximately 80% of all temporal bone fractures. ²⁹ The transverse fractures run at right angles to the longitudinal axis and account for about 20% of all temporal bone fractures. ²⁹ Fractures with both components are described as complex or mixed. Dahiya et al ³⁰ have proposed a classification of temporal bone fractures with an emphasis on the integrity of the otic capsule. This classification offers the advantage of correlating radiographic utility and stratification of clinical severity, including severity of Glasgow Coma Scale scores and intracranial complications, such as subarachnoid hemorrhage and epidural hematoma. The presence of an otic capsule violating fracture is significantly more likely to be associated with the latter two complications. ³⁰ For complete evaluation, in addition to the fracture lines, special note should be made of the following: 1) ossicular injury, 2) facial nerve injury, 3) integrity of the tegmen tympani, 4) bony labyrinth, 5) mastoid air cells, and 6) carotid canal.

Longitudinal fractures are the most common type of temporal bone fractures and usually result from a lateral blow in the temporo-mastoid region. The longitudinal fractures are subdivided into an anterior and a posterior type. The anterior type course along the anterior aspect of the squamous temporal bone and extend along the roof of the external canal, tegmen tympani, and end in the region of the geniculate ganglion. The posterior type course along the posterior aspect of the squamous temporal bone and extend through the mastoid air cells, posterior wall of the external canal, through the tympanic cavity, and terminate in the region of the geniculate ganglion. The inner ear structures are usually spared because the fracture paths of least resistance are extralabyrinthine. ^31,32

Conductive hearing loss commonly accompanies the longitudinal fracture, which may be transient due to hemotympanum or a ruptured tympanic membrane. However, ossicular injury may occur in approximately 50% of patients and result in persistent conductive hearing loss. ²⁸ The most easily dislocated ossicle is the incus, resulting from the disruption of the incudostapedial joint. The incudomallear dislocation is less common (Figure 10). Facial nerve injury, usually delayed and incomplete, occurs in only 10% to 20% of patients with longitudinal fractures. ^33-35 Transverse fractures are subdivided into a lateral and a medial type, according to their relationship to the arcuate eminence. The lateral type of fracture extends across the vestibule, basal turn, and promontory of the cochlea, posterior and lateral semicircular canals. The medial type of fracture extends across the internal auditory canal.

Transverse fractures are almost always accompanied with sensorineural hearing loss, either due to transection of the cochlear nerve or cochlear injury. Vertigo, dizziness, and tinnitus may result from injury to vestibular nerves, the vestibule, the semicircular canals, and the vestibular aqueduct associated with transverse fractures. Facial nerve injury may occur in 30% to 50% of patients, and immediate facial nerve paralysis is usually indicative of nerve transection or severe compression by fracture fragments. Delayed onset of facial nerve paralysis may be secondary to fracture of the facial nerve canal, with associated contusion, edema, or intraneural hematoma. A facial nerve hematoma can be recognized as a high-signal intensity region on the unenhanced T1-weighted images, and the damaged nerve segment can appear as a thickened, strongly enhancing region on gadolinium-enhanced T1-weighted images. ³⁶

Other complications of trauma include CSF otorhinorrhea, perilymph fistula, posttraumatic meningocele, and meningoencephalocele. Cerebrospinal fluid otorhinorrhea is usually due to dural tear from fractures of the tegmen, most commonly as a consequence of a longitudinal fracture. Disruption of the mastoid, the internal auditory canal, and the petrous air cells are other causes of otorhinorrhea. High-resolution CT cisternography is the most useful study for the localization of the site of CSF leak. Persistent vertigo may indicate a perilymph fistula. These result from a tear either in the round window membrane or in the ligamentous attachment of the stapedial footplate and are often undetectable on CT. In the absence of a demonstrable fracture, the presence of pneumolabyrinth is highly suggestive of this entity. ³⁷ Internal carotid artery occlusion or pseudoaneurysm and jugular vein-sigmoid sinus laceration or occlusion are other potential complications that can occur when these vessels are in the path of the fracture line.

Laryngeal fractures

The incidence of laryngotracheal trauma is estimated to be 1 in 30,000 emergency department visits in the United States. ^38-40 These injuries result from motor vehicle collisions in the adult population, and from accidents involving contact sports and hanging type injuries in the young adult, adolescent, and pediatric populations. A wide spectrum of injuries may be encountered. High-resolution spiral CT imaging is the modality of choice, due to its ability to obtain volumetric data acquisition and retrospectively generate thin axial sections and, subsequently, optimal multiplanar and 3D reconstructed images.

Blunt trauma to the larynx may result in soft-tissue injuries with or without associated framework injuries. ⁴¹ If large enough or strategically located, endolaryngeal edema or hematoma will produce a significant narrowing of the airway. It can occur in three specific locations: in the pre-epiglottic space, in the paralaryngeal space, and in the mucosal space. ^42-44 Posttraumatic changes in the CT appearance of the false and true cords may relate to the presence of edema, hematoma, laceration, or avulsion. The thyroid and cricoid cartilages interact dynamically to protect the airway from blunt injury. ^42-44 The thyroid cartilage may reveal single or multiple fractures in both the vertical and horizontal plane, depending on the degree of the impact. Although the cricoid ring is shielded initially by the anterior projection of the thyroid cartilage, it may reveal a single median fracture or multiple paramedian vertically oriented fractures with forceful impact and pose a danger of airway collapse (Figure 11). The true cords may be paralyzed as a consequence of an injury to the recurrent laryngeal nerve or dislocation of the cricoarytenoid or cricothyroid joints. The former dislocation typically manifests by an anterior and medial dislocation of the involved arytenoid cartilage. ^18,42-44 Frequently a paralyzed, paramedian vocal cord is present. ^18,44-46 Dislocations of the cricothyroid joint manifest by widening of the cricothyroid space. ^18,44

If the force is severe or low in the neck, complete laryngotracheal separation may occur. ^47-49 Separation usually occurs between the cricoid cartilage and the first tracheal ring, resulting in displacement of the trachea inferiorly and soft-tissue collapse into the airway, with consequent airway obstruction. Other specific CT signs include nonalignment of the laryngotracheal airway on serial CT images, abrupt decrease or increase in airway caliber on sequential images, the presence of a ragged or misshapen airway or the formation of a false passage. ^50-53 The primary concern in the initial management of patients with laryngotracheal trauma is the establishment and maintenance of an adequate airway.

Conclusion

Clinical examination is often limited in patients with trauma to the head and neck region due to obscuration by overlying edema, hemorrhage, and soft-tissue injury. High-resolution CT is essential for accurate delineation of bony and soft-tissue injuries. AR