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Computed Tomographic Imaging in Head and Neck Trauma: What the Radiologist Needs to Know
Computed Tomographic Imaging in Head and Neck Trauma: What the Radiologist Needs to Know Edward K. Sung, MD, Rohini N. Nadgir, MD, and Osamu Sakai, MD, PhD
T
he American College of Surgeons’ National Trauma Databank of the year 2011 reported 722,824 incidents of trauma during the year 2010.1 Falls contributed to the major mechanism of injury (38.4%), followed by motor vehicle collisions (28.9%). Injuries from mechanisms of being struck (7.5%), cut/pierced (4.7%), or related to firearms (4.5%) were much less common. Injuries to the head and face combined accounted for 59.7% of cases.1 As such, it is apparent that head- and neck-related trauma is a major source of injury in the United States. In the trauma setting, rapid access to imaging is important in making diagnoses and guiding management decisions for the trauma team. In the acute setting, multidetector-row computed tomography (CT) is becoming the imaging modality of choice. This is because of its wide availability throughout most hospitals and its ability to acquire images rapidly. In certain settings, CT angiography (CTA) is being increasingly used to evaluate for trauma-related vascular injuries, as opposed to conventional angiography. Although conventional angiography remains the gold standard for evaluating vascular injury, it is an invasive procedure, which is more time and labor intensive, and is not as widely available as CTA. Magnetic resonance imaging (MRI) and MR angiography are not as commonly used as CT and CTA in the setting of acute trauma because they are more time intensive and not compatible with certain life-support equipment.2 We provide a review of the different types of injuries and their imaging features that may be encountered in the setting of head and neck trauma, with a focus on CT.
Head A noncontrast CT of the head is usually the first imaging modality of choice in the setting of head trauma. Typical imaging protocols when imaging the head should include the skull base through the vertex. At our institution, images of the brain are obtained axially using 5-mm slice thickness, with axial 1.25-mm reconstructions in soft-tissue and bone algorithms. Coronal 5-mm soft-tissue reconstructions are also routinely performed to aid in detection of subtle intracranial hemorrhages.3
Soft-Tissue Injuries Trauma to the head frequently results in superficial soft-tissue injuries, including subcutaneous hematomas and lacerations. The presence of superficial soft-tissue injuries should raise suspicion for underlying fractures or intracranial injuries.
Department of Radiology, Boston Medical Center, Boston University School of Medicine, Boston, MA. Address reprint requests to Rohini N. Nadgir, MD, Department of Radiology, Boston Medical Center, Boston University School of Medicine, 820 Harrison Avenue, FGH Building, 3rd Floor, Boston, MA 02118. E-mail: [email protected]
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Skull Fractures Skull fractures may be linear, comminuted, or depressed. In children, diastatic fractures are more common.4 Three-dimensional (3D) volume-rendered reconstructions of the skull can aid in detection of skull fractures in the axial plane, particularly in pediatric patients. The presence of any skull fractures should always lead to closer evaluation for intracranial injuries such as intracranial hemorrhage or contusions. Attention should be given to the intracranial region directly beneath the fracture site and the region opposite the fracture (contrecoup injury).
Orbits Traumatic orbital injuries account for up to 3% of all emergency room visits in the United States, and are most commonly due to motor vehicle collisions and sports-related injuries.5 CT is the imaging modality of choice to evaluate for orbital injury. Optimal protocols for CT orbital imaging should include thin-section axial images and multiplanar reformats in soft-tissue and bone algorithms. At our institution, 1.25-mm axial images are obtained through the orbits, with 1.5-mm/1.5-mm coronal and sagittal reconstructions in soft-tissue and bone algorithms.
Fractures Fractures of the orbit commonly involve one (48%) or two (30%) orbital walls.6 The orbital floor and medial wall are the weakest structures and are therefore the most susceptible to injury.6 Orbital wall fractures may occur in conjunction with other facial fractures, such as zygomaticomaxillary complex (ZMC), nasoethmoid, frontal bone, and LeFort fractures.6,7 A traumatic force directed toward the eye can cause increased intraorbital pressure, which transmits outwardly along the orbital walls. This pressure leads to a blow-out type orbital fracture (Fig. 1). The orbital floor and medial walls are the most susceptible to blow-out fractures, sparing the orbital rim.8 High-energy trauma can rarely lead to fractures at the level of the orbital apex, the deepest portion of the orbit. Fractures at this location typically require urgent surgical treatment because of the high incidence of associated optic nerve injury.
Soft-Tissue Injuries Acute bony orbital injuries are often accompanied by periorbital soft-tissue swelling/hematoma,6 and such a finding should prompt a thorough evaluation for bony injury. Fractures of the orbital floor may affect the infraorbital nerve as it passes through the infraorbital canal. Involvement of this canal should raise suspicion for nerve injury and should be evaluated clinically. In the setting of blow-out fractures, the fracture mechanism allows for the possibility of extraocular muscle entrapment. Although muscle entrapment remains a clinical diagnosis, certain imaging features may suggest entrapment, including displacement of the extraocular muscle, penetration of muscle by bone fragment or foreign body material, or an abnormal contour of the extraocular muscle. Optic nerve injuries are rare, seen in up to 2% of orbital
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321 CT is highly suggestive of globe rupture (Fig. 2). However, widening of the anterior chamber, secondary to decreased intraocular pressure, may be the only sign of globe rupture in more subtle cases.9 Other indirect signs of possible globe rupture include the presence of intraocular air or foreign bodies (Fig. 3). Traumatic eye injuries can also disrupt the internal structures of the globe. The lens can be dislocated partially or completely and can be seen layering dependently in the globe on CT. The retina can also become detached as a result of trauma. The retina is firmly fixed along its anterior and posterior attachments, while it is loosely attached elsewhere. Therefore, the subretinal fluid in retinal detachment typically appears V shaped, with the apex at the optic disc.5 Choroidal hemorrhages are typically crescentic or parallel in configuration and characteristically spare the region of the optic disc, at the posterior third of the globe, because of the anchoring effect of ciliary vascular and neuronal tissues.10 Focal subhyaloid hemorrhages may rarely be seen in the setting of intracranial subarachnoid hemorrhage, often referred to as Terson syndrome.11 Globe trauma can disrupt the vasculature without affecting the structural integrity of the globe, which can lead to hemorrhage within the globe. Hemorrhage within the anterior chamber (hyphema) is usually apparent clinically; however, vitreous hemorrhage may not be as obvious clinically and may be more readily appreciable on imaging. On CT, vitreous hemorrhage appears as focal or diffuse hyperdensity within the vitreous body. Carotid– cavernous fistulas may form as a result of head trauma. Carotid– cavernous fistulas are clinically characterized as diplopia, proptosis, and chemosis, which can occur in the post-traumatic setting. A traumatic tear in the cavernous segment of the internal carotid artery (ICA) creates a fistulous connection with the cavernous sinus, causing increased cavernous sinus pressure. This increased pressure can transmit to the ophthalmic vein, leading to unilateral or bilateral dilation, which can be appreciated on noncontrast CT. On CTA, the typical findings may include an asymmetrically enlarged ipsilateral cavernous sinus of similar attenuation to opacified arterial structures, enlargement of the dural venous sinuses, enlargement and tortuosity of the superior ophthalmic vein, enlargement of the extraocular muscles, proptosis, and subchoroidal effusions.12
Midface Facial injuries are seen in up to 25% of trauma cases, and ⬎150,000 patients present to the emergency room with facial trauma annually, most commonly in the setting of motor vehicle collisions.13 Optimal protocols for CT imaging of the facial bones should include thin-section axial images and multiplanar reformats in soft-tissue and bone algorithms. At our institution, 1.25-mm axial images are obtained through the facial bones, with 1.5-mm/1.5-mm coronal and sagittal reconstructions in soft-tissue and bone algorithms.
Figure 1 A 45-year-old man with an orbital blow-out fracture after assault. (A) Coronal computed tomographic (CT) image demonstrates depressed defect of the left orbital floor (white arrow) with associated hemorrhage and orbital gas present in the inferior orbit (black arrow). Note relative enlargement of the inferior rectus muscle, which suggests intramuscular hematoma. (B) Sagittal CT image shows the depressed fracture fragment (white arrow) and preservation of the orbital rim (black arrow). fractures,6 but should be suspected when fractures are seen extending into the optic canal. Stretching of the optic nerve may also be seen in the setting of traumatic proptosis, and it requires urgent ophthalmologic evaluation owing to a high risk of development of blindness. Orbital trauma can also lead to various injuries of the globe, seen in up to 5% of cases of isolated orbital fractures.6 Blunt or penetrating trauma can disrupt the normal spherical shape of the globe, leading to globe rupture, which is a major cause of blindness.5 An abnormal contour of the globe on
Figure 2 A 61-year-old woman who sustained head trauma and globe rupture. Axial CT image shows enlargement and deformity of the left globe contours and vitreous hemorrhage.
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arch, lateral orbital wall, anterior maxillary wall, and posterolateral maxillary wall (Fig. 4). The degree of displacement or comminution of the fracture fragments may affect surgical management. Orbital floor fractures are present in up to 44% of ZMC fractures.7,8
LeFort Fractures
Figure 3 A 37-year-old woman after fall. Coronal CT image shows extensive left periorbital swelling and punctate radiopaque foreign body material within the left globe (black arrow), indicating penetrating injury and violation of the globe. Note otherwise preserved morphology of globe contours.
When needed, 3D volume-rendered reconstructions are obtained to aid in fracture analysis and surgical planning.
Frontal Sinus Fractures Frontal sinus fractures account for 5%-15% of maxillofacial fractures.8 The frontal bone is structurally among the strongest of the facial bones and requires a high-energy force to cause a fracture.8 The frontal sinus consists of anterior and posterior tables (or walls). Anterior table fractures are usually managed conservatively, especially for nondisplaced fractures. Displaced anterior table fractures may lead to cosmetic deformities, necessitating surgical repair.8 Posterior table fractures are treated more aggressively because of the potential for intracranial violation. Nondisplaced fractures of the posterior table may still be treated conservatively with close imaging follow-up, but comminuted or displaced posterior fractures warrant surgical exploration owing to the increased risk of intracranial complications.8 As such, imaging evaluation of frontal sinus fractures should identify involvement of the anterior table, posterior table, or both, and displacement of fracture components should be characterized. With posterior table fractures, a thorough evaluation for signs of dural violation, including hemorrhage or pneumocephalus, is necessary. Long-term complications of frontal sinus fractures can include formation of mucoceles and mucopyoceles. These complications are more common when the fracture involves the nasofrontal duct, which can lead to obstruction of frontal sinus outflow. Other complications can also include osteomyelitis and abscess formation in the epidural or subdural spaces.8
Naso-orbitoethmoid (NOE) Fractures NOE fractures involve the nasal bone, medial orbital wall, and ethmoid bone. NOE fractures typically require higher energy forces compared with isolated nasal bone fractures, and are usually characterized based on the degree of comminution at the attachment of the medial canthus, as well as the integrity of the medial canthal tendon. The degree of bony injury is important to note for the surgeons because it may affect their approach to surgical management. NOE fractures are commonly associated with injuries of the cribriform plate, nasofrontal duct, and globe.7,8
The LeFort classification describes the various complex facial fracture patterns that cause separation of the maxilla from the skull base. LeFort fractures are seen in up to 26% of facial fractures.7,8,14 In the setting of complex facial injuries, certain fracture patterns may help characterize LeFort fracture types.14 All LeFort fracture types involve the pterygoid process. LeFort I fractures are the only type to involve the anterolateral margin of the nasal fossa. LeFort II fractures are the only type to involve the inferior orbital rim. LeFort III fractures are the only type to involve the zygomatic arch. These unique patterns can be used to distinguish between the different LeFort fractures. When evaluating for LeFort fractures, the clinician and radiologist should be aware that the different types of LeFort fractures can occur synchronously and may also occur in conjunction with other types of facial fractures, such as ZMC and NOE injuries. Additionally, LeFort fractures do not always occur symmetrically (Fig.5).
Parotid Gland Injuries The parotid glands are rarely injured in blunt and penetrating head trauma.15 The bulk of the parotid gland lies over the mandibular ramus, posterior to the masseter muscle. The parotid duct (Stensen’s duct) courses anteriorly, superficial to the masseter muscle. In the setting of trauma, the superficial portion of the gland is more susceptible to injury, and the parotid duct is especially vulnerable owing to its superficial course. Parotid ductal injury should be suspected when lacerations or penetrating injuries occur along the path of the duct. Other important structures that may be affected in conjunction with parotid gland injuries include trauma to the facial nerve, facial artery, and retromandibular vein.15 When parotid gland injuries involve the duct, complications rates can be as high as 80% with nonsurgical management.15 Late complications of parotid gland injuries can include external parotid fistulas, ductal strictures, and sialocele formation (Fig. 6). External parotid fistulas can develop within the first week after injury, and they typically present as clear secretions that occur with mastication. Sialoceles develop more slowly, typically up to two weeks after the injury. On imaging, they can be difficult to distinguish from hematoma or seroma. Gustatory lacrimation (tear formation with salivation) is a rare, but troublesome, complication that can occur after facial nerve injury because of aberrant regeneration of facial nerve fibers toward the pterygopalatine fossa to innervate the lacrimal gland.15
Mandible The mandible has been described as the most commonly fractured facial bone in the setting of motor vehicle collisions.16 With its articulation at the skull base, the mandible is commonly thought of as a closed ring. Hence, the presence of a fracture should raise suspicion for a second fracture. However, because the mandible is not completely fixed at the temporomandibular joint, unifocal fractures do occur frequently.16 The most common locations of mandibular fractures include the angle (30%), followed by the body (26%), parasymphyseal region (16%), and condyle (12%).16 When mandibular fractures are identified, the degree of displacement or comminution should be evaluated (Fig. 7). Extension of the fracture through the mandibular canal should also be noted, as it may be an indication of alveolar nerve injury. In addition, the presence of any associated tooth fractures or tooth loosening should be thoroughly evaluated, as these are susceptible to aspiration, particularly in a patient who is unconscious.
ZMC Fractures In the setting of blunt facial trauma, ZMC fractures are the most common type of facial fractures.7,8 ZMC fractures are considered quadripod fractures, involving break points around the 4 sutural connections of the zygoma: the zygomaticofrontal, zygomaticotemporal, zygomaticomaxillary, and zygomaticosphenoid sutures. These correspond to fractures involving the zygomatic
Temporal Bone The temporal bone is divided into five segments: squamous, mastoid, petrous, tympanic, and styloid. Several major vessels course through the temporal bone, including the ICA, middle meningeal artery, sigmoid sinus, and
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Figure 5 A 50-year-old male bicyclist who was struck by a car, with multiple LeFort injuries. 3D volume-rendered image shows bilateral LeFort I (widely spaced dots), bilateral LeFort II (less widely spaced dots), and unilateral LeFort III (narrowly spaced dots) injuries. Note associated zygomaticomaxillary complex fracture component (arrow), as well as bilateral mandibular fractures. jugular bulb. The temporal bone also contains the inner ear structures (cochlea, semicircular canals, and internal auditory canal), as well as the middle ear cavity, which houses the ossicles. Because of the fine bony anatomy of the temporal bone, optimal CT imaging protocols should include thin-section (preferably submillimeter) axial images with multiplanar reformats in bone algorithms. Helically acquired data can provide overlapping thin-section images for greater anatomic detail; however, in the trauma setting, thin-section axially acquired data from noncontrast head CT can provide satisfactory anatomic detail without exposing the patient to additional radiation.17 In addition, CT angiography or CT venography should be considered when there is suspicion for associated arterial or venous sinus injury.
Fractures Temporal bone injury can occur in up to 22% of patients with skull fractures.17 Common causes include motor vehicle collisions, falls, and assaults. In the setting of trauma, the most commonly injured portions of the temporal bone include the petrous and mastoid segments. Fractures are traditionally classified as transverse (perpendicular to the axis of the temporal bone)
Figure 4 A 59-year-old man with zygomaticomaxillary complex fracture after a fall. (A) Axial CT image shows comminuted disruption of the anterior (white arrow) and posterolateral (black arrow) walls of the left maxillary sinus. There is depressed deformity of the zygomatic arch (arrowhead). Note disruption of the infraorbital nerve canal. (B) More superiorly, there is comminuted disruption of the lateral orbital wall on the same side (white arrow). (C) 3D volume-rendered image shows the anterior maxillary (black arrows), lateral orbital wall (white arrow), and zygomatic arch (arrowhead) fractures.
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poral bone.17 Occult nondisplaced temporal bone fracture should be considered when these findings are noted in the trauma setting.
Ossicular Injuries Hearing loss as a result of trauma can be due to laceration of the tympanic membrane, hemotympanum, or injury to the ossicles. Ossicular injuries can be seen in up to 32% of temporal bone traumas.18 Dislocation of the ossicles is a more common manifestation of ossicular injuries than fractures. The malleus and stapes have firm attachments, whereas the incus is less firmly suspended between the other two; therefore, the incus is most prone to dislocation.18 Incudomalleolar joint separation has a typical appearance on axial CT images, with a displaced “ice cream scoop” (malleolar head) from the “ice cream cone” (short process of incus).
Figure 6 A 27-year-old man with parotid duct injury after assault. (A) Axial CT image shows edema and soft-tissue stranding overlying the expected course of Stenson’s duct (arrow). Surgical exploration with duct repair and stent placement was performed subsequently. (B) Axial CT image a year later shows development of dilated duct (arrow) because of the stricture at the outlet of Stenson’s duct, despite surgical intervention.
or longitudinal (parallel to the axis of the temporal bone). Longitudinal fractures are more common, seen in approximately 70%-90% of cases.17 Temporal bone fractures can also be categorized as otic capsule violating or sparing. Otic capsule–violating fractures involve injury to inner ear structures and are associated with more complications, such as facial paralysis, cerebrospinal fluid (CSF) leak, or profound hearing loss (Fig. 8).17 Temporal bone fractures that involve the carotid canal may have associated vascular injuries of the petrous segment of the ICA, such as dissection, pseudoaneurysm, transection, or occlusion. Such vascular complications can be seen in up to 11% of fractures that involve the carotid canal.17 Additionally, given the proximity of the sigmoid sinus to the temporal bone, a fracture can also lead to venous injury, with resulting thrombosis (Fig. 9). Some temporal bone fractures may be radiographically occult and only demonstrate secondary signs of fracture. These signs may include opacification of the mastoid air cells or middle ear, air–fluid levels in the sphenoid sinus, and pneumocephalus or extra-axial hemorrhage adjacent to the tem-
Figure 7 A 40-year-old woman with mandibular fracture after assault. (A) Axial CT image shows unilateral displaced fracture at the posterior body of the mandible on the left. Note disruption of the mandibular canal (black arrow). (B) 3D volume-rendered image shows degree of override of the fracture fragments, which aided in the surgical planning approach.
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Skull Base Frontobasal Injuries Frontobasal (anterior skull base) injuries represent 3%-5% of all craniomaxillofacial fractures, and are usually the result of blunt trauma, motor vehicle collisions, or falls.19,20 These fractures can involve isolated linear fractures of the cranial base (type 1), linear fractures of the cranial base and frontal bone (type 2), or comminuted fracture of the entire frontal bone segment and orbital roof (type 3). Frontobasal injuries are usually associated with other facial fractures, most commonly NOE fractures, followed by LeFort Type III fractures.19,20 Frontobasal injuries are typically the result of high-energy impact and are therefore prone to more complications. Violation of the dura can lead to a dural fistula, with complications including CSF leak, rhinorrhea, or pneumocephalus. These complications increase the risk of meningitis, especially in the setting of persistent CSF leak lasting ⬎2 weeks.19,20
Basilar Skull Injuries Basilar skull fractures can be seen in up to 30% of head injuries.21 Unilateral and bilateral occipital condylar fractures are seen in high-energy impact injuries and can be associated with additional brain and cervical spine injuries. These are often associated with ligamentous soft-tissue injury demonstrable by MRI and require surgical stabilization.22 Additional vascular injuries including dissections and pseudoaneurysms of the internal carotid and vertebral arteries, as well as dural arteriovenous fistulas (AVF), can occur.23
Neck Injury to the soft-tissue neck can occur with blunt or penetrating trauma. When there is suspicion for vascular injury, CTA should be considered as the initial imaging modality for diagnosis and guiding management.24 CTA can be timed for arterial or venous phases depending on clinical suspicion. After timed bolus contrast injection, helically acquired submillimeter axial images through the neck should be obtained and evaluated in conjunction with maximum intensity projection reformations in axial, coronal, and sagittal planes. At our institution, we obtain 0.625-mm axial images from the aortic
Figure 8 A 20-year-old woman involved in rollover motor vehicle collision with temporal bone fracture. Axial CT image shows transversely oriented defect through the otic capsule structures including the vestibule and vestibular aqueduct (white arrow). Note associated air, pneumolabyrinth, within the basal turn of the cochlea (black arrow).
Figure 9 A 21-year-old woman involved in motor vehicle collision with temporal bone fracture and venous thrombosis. (A) Axial CT image shows longitudinally oriented fracture through the mastoid (black arrows) and petrous segments of the temporal bone extending to involve the carotid canal (large white arrow). Note air adjacent to the carotid canal and within middle cranial fossa. There is diastasis of the occipitomastoid suture (arrowhead) with tiny pockets of gas at the expected location of the sigmoid sinus (small white arrow). (B) Computed tomography angiographic (CTA) image demonstrates patency of the left internal carotid artery (ICA) (not shown), but confirms presence of filling defect within the left sigmoid sinus (black arrow), consistent with nonocclusive thrombus.
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E.K. Sung, R.N. Nadgir, and O. Sakai With more severe injury, a dissection can occur where the intima is torn away from the other layers of the vessel. This leads to a raised intimal flap, which typically appears as a linear intraluminal filling defect. With even more severe injury, an intramural hematoma may develop, which can appear as eccentric or circumferential mural thickening. On imaging, the arterial lumen will be narrowed, but the overall diameter of the injured vessel may be increased. If large enough, this can result in complete occlusion of the vessel (Fig. 11).12,29,31 In the setting of blunt trauma, arterial dissection is the most common injury.31 Pseudoaneurysms can also develop as a result of blunt vascular injury. They are not true aneurysms in that they do not contain the normal layers of an artery. Rather, the extravasating blood from a focal injury in the artery becomes locally contained by the surrounding perivascular connective tis-
Figure 10 A 42-year-old construction worker (male) after a beam fell on his neck. Axial CT image shows acute fracture of the tracheal cartilage (arrow). Adjacent air in the overlying soft tissues is strongly suggestive of associated tracheal injury, although the precise focus of injury could not be identified on imaging.
arch to the level of circle of Willis with maximum intensity projection images (5-mm thickness and 2-mm interval) in all three planes.25
Blunt Soft-Tissue Neck Injury Injury to the soft-tissue structures of the neck, including the pharynx, esophagus, larynx, and trachea, are extremely rare in the setting of blunt trauma.26,27 The larynx and trachea are more susceptible to injury owing to their superficial positioning. Blunt laryngotracheal injuries can occur with high-impact direct blow injuries or crush injuries.27 Although penetrating laryngotracheal injuries are more frequent and significant, blunt laryngotracheal injuries are less readily apparent clinically and may require imaging for diagnosis.28 Therefore, in the setting of blunt neck trauma, the radiologist should thoroughly assess the larynx and trachea and look for secondary signs of laryngotracheal injury such as unexplained subcutaneous gas, thyroid or cricoid cartilage fractures, or adjacent hematomas (Fig. 10). Care should be taken to distinguish subcutaneous gas in the neck related to laryngotracheal injury from gas tracking superiorly from a pneumothorax or pneumomediastinum. The accurate identification of laryngotracheal injuries is extremely important because of the potential for life-threatening airway compromise.26-28
Blunt Cereberovascular Injury The prevalence of cerebrovascular injury among all patients with blunt trauma can be up to 1.6%.12 The major cause of morbidity and mortality related to blunt cerebrovascular injury is brain infarction. Morbidity and mortality rates for blunt carotid artery injury range from 32% to 67% and 17% to 38%, respectively.12,29 With blunt vertebral artery injury, the morbidity and mortality rates are lower, ranging from 14% to 24% and 8% to 18%, respectively.12,29 Although traumatic arterial injuries can occur without fractures, the risk is significantly increased with the presence of any major facial, skull, or cervical spine fracture, as well as in the setting of a high-impact trauma.30 The risks of arterial injury are highest in patients with cervical interfacetal subluxations, followed by fractures that extend into foramen transversarium and the ICA canal.30 For these reasons, CTA evaluation for arterial injury is recommended in the setting of high-impact mechanisms of injury, regardless of the presence of a fracture, low-impact mechanisms of injury if there is a fracture reaching the expected location of an arterial structure, or presence of cervical interfacetal subluxation. The degree of injury to an artery can be variable, and includes intimal injury, pseudoaneurysm, occlusion, or complete arterial transection. Formation of AVF can also occur. Minimal intimal injury will typically appear as areas of nonstenotic luminal irregularity, and can be difficult to distinguish from vasospasm.
Figure 11 A teenage boy, choked, with ICA dissection. (A) CTA performed because of the trauma mechanism shows abrupt tapered occlusion of the ICA (black arrow), consistent with dissection on sagittal maximum intensity projection (MIP) reformats. (B) Axial T2-fat suppressed image from magnetic resonance imaging performed for left-sided weakness after the event shows intramural and extramural hematoma (white arrow), confirming dissection. Diffusion images confirmed cerebral infarct in the right middle cerebral artery distribution (not shown).
CT imaging in head and neck trauma sue. Therefore, pseudoaneurysms typically appear as eccentric outpouchings of contrast material on imaging, and can vary considerably in shape and size. In comparison, complete transection of an artery will cause active hemorrhage, which appears as an irregular collection of extravascular contrast, typically surrounding or adjacent to the injured vessel.12,29 Arterial injury can also lead to the formation of an AVF. On CTA, venous structures near the AVF will demonstrate early enhancement during the arterial phase, similar in density to adjacent arterial structures, and the fistulous connection may be visualized. However, findings are often subtle, and suboptimal arterial-phase imaging techniques can make it difficult to
327 visualize the early enhancement of the veins.12,29 When clinical suspicion is high, conventional angiography may follow for clarification and/or treatment purposes.
Penetrating Trauma Penetrating injuries of the neck can involve multiple structures including arteries, veins, esophagus, and trachea (Fig. 12). Owing to the mechanism, vascular injuries of the neck occur more commonly after penetrating trauma compared with blunt trauma.32 As such, the morbidity from arterial injuries
Figure 12 A 31-year-old man after nail-gun accident. (A) Sagittal MIP reformat from CTA shows penetrating object violating trachea and likely involving esophagus based on trajectory. (B) Coronal MIP reformat shows nail abutting the brachiocephalic artery (arrow), but owing to beam-hardening artifact, focal vessel injury could not be entirely excluded. (C) Conventional angiogram confirms patency of the brachiocephalic artery, with slight focal extrinsic deformation along the medial wall of the vessel by the nail (arrow).
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328 is usually related to neurologic damage from strokes, and mortality rates can be as high as 10%.33,34 In the setting of penetrating neck trauma, the neck is divided into three zones: zone I extends from the sternal notch and clavicles to the cricoid cartilage; zone II extends from the cricoid cartilage to the angle of the mandible; and zone III extends from the mandible to the base of the skull. The management of penetrating neck injuries has been controversial, with traditional guidelines recommending surgical exploration for any penetrating injuries in zone II and reserving nonsurgical evaluation, including angiography, endoscopy, and laryngoscopy, for injuries in zones I and III because of the difficulty in accessing these regions surgically. However, in recent years, CT and CTA have become increasingly used as methods for the initial evaluation of penetrating neck injuries in all zones, which allows for even more selective surgical exploration.33-36 In the imaging evaluation of penetrating neck trauma, determining the trajectory of the penetrating object can be of great importance in identifying the structures at risk for injury. Depending on the nature of the material, penetrating objects have variable densities on CT scans. Metallic densities (ie, bullet fragments) can contribute to significant beam-hardening artifact, which can limit evaluation of adjacent structures. In these settings, it is imperative to evaluate for the presence of metallic material within critical structures including the orbit and spinal canal, as these are contraindications to further imaging by MRI. The radiologist should be aware that woodenpenetrating objects may be difficult to distinguish from air on CT, and evaluation should include assessment at wider window settings to increase conspicuity of the object trajectory.37 Up to 25% of penetrating neck injuries can result in arterial injuries, with the carotid arteries involved more than the vertebral arteries, owing to their superficial location.33 Similar to blunt trauma, arterial injury from penetrating trauma can include intimal injury, dissection, partial or complete occlusion, pseudoaneurysm, or AVF formation. However, when compared with blunt trauma, dissections occur less frequently and the incidence of arterial occlusion and transection is higher in penetrating injuries.31,33 For the detection of arterial injuries in the neck, CTA has been shown to have a sensitivity and specificity ⬎90%.33,34 Venous injuries are more common in the setting of penetrating injuries compared with blunt trauma.31 Injuries to the neck veins have been seen in up to 51% of penetrating neck injuries; however, they are more commonly clinically silent when compared with arterial injuries.38 Venous injuries often present as occlusions or pseudoaneurysms.31 In addition, a concurrent injury to a vein and artery in the same region can lead to the development of an AVF. Esophageal injuries are uncommon and seen in up to 6% of patients with penetrating trauma.27,33,36,39 On imaging, if the suspected penetration tract is far from the esophagus, esophageal injury can be excluded. However, pockets of gas along the tract in the expected vicinity of the esophagus should raise suspicion for injury. This should not be confused with a tracheal diverticulum, which is a common normal anatomic variant, seen as a focal collection of gas in the tracheoesophageal groove region on the right. When esophageal injury is suspected, direct visualization with endoscopy is necessary. Alternatively, a barium-swallow examination may be considered, although it may be technically difficult in an acutely injured patient. A delayed diagnosis of an esophageal injury can lead to complications, including abscess formation, mediastinitis, and sepsis, with mortality rates as high as 20%.27,33,36,40 Laryngeal and tracheal injuries are also uncommon, seen in 2%-7% of patients with penetrating neck trauma.27,33,36 However, the potential for this injury should always be considered in the setting of penetrating neck injuries because of the risk of life-threatening airway compromise. Evaluation for laryngotracheal injuries should be based on clinical assessment, imaging findings, and endoscopy. Similar to esophageal injuries, the presence of extraluminal gas near the larynx or trachea should raise suspicion for an airway injury. Long-term complications of tracheolaryngeal injury can include dysphonia, stenosis, or dysphagia.27,33
Conclusions Traumatic injuries to the head and neck and resulting complications are a major cause of morbidity and mortality, necessitating rapid clinical and
radiologic assessment. In the acute setting, CT is becoming the imaging modality of choice. The role of the radiologist is to recommend the appropriate imaging protocols to best evaluate the region of interest and to identify the many different patterns of bone and soft-tissue injuries in these regions. In the imaging evaluation of patients with potential traumatic head and neck injuries, the radiologist should be aware of the acute imaging findings of these injuries and have a thorough understanding of potential short-term and long-term complications.
References 1. American College of Surgeons. National Trauma Data Bank, 2011 Annual Report. Available at: http://www.facs.org/trauma/ntdb/pdf/ ntdbannualreport2011. Accessed April 2012 2. Barest G, Nadgir RN, Mian AZ, et al: Traumatic and non-traumatic emergencies of the brain, head, and neck, in Soto JA, Lucey BC (eds): The Requisites: Emergency Radiology. Philadelphia, PA, Mosby, 2009, pp 1-59 3. Wei SC, Ulmer S, Lev MH, et al: Value of coronal reformations in the CT evaluation of acute head trauma. AJNR Am J Neuroradiol 31:334-339, 2010 4. Mulroy MH, Loyd AM, Frush DP, et al: Evaluation of pediatric skull fracture imaging techniques. Forensic Sci Int 214:167-172, 2012 5. Kubal WS: Imaging of orbital trauma. Radiographics 28:1729-1739, 2008 6. Karabekir HS, Gocmen-Mas N, Emel E, et al: Ocular and periocular injuries associated with an isolated orbital fracture depending on a blunt cranial trauma: Anatomical and surgical aspects. J Craniomaxillofac Surg 2011 November 15 (Epub ahead of print) 7. Hopper RA, Salemy S, Sze RW: Diagnosis of midface fractures with CT: What the surgeon needs to know. Radiographics 26:783-793, 2006 8. Fraioli RE, Branstetter BF, Deleyiannis FW: Facial fractures: Beyond LeFort. Otolaryngol Clin North Am 41:51-76, 2008 9. Weissman JL, Beatty RL, Hirsch WL, et al: Enlarged anterior chamber: CT finding of a ruptured globe. AJNR Am J Neuroradiol 16(suppl 4):936-938, 1995 10. LeBedis CA, Sakai O: Nontraumatic orbital conditions: Diagnosis with CT and MR imaging in the emergent setting. Radiographics 28:17411753, 2008 11. Swallow CE, Tsuruda JS, Digre KB, et al: Terson syndrome: CT evaluation in 12 patients. AJNR Am J Neuroradiol 19:743-747, 1998 12. Sliker CW: Blunt cerebrovascular injuries: Imaging with multidetector CT angiography. Radiographics 28:1689-1710, 2008 13. Sitzman TJ, Hanson SE, Alsheik NH, et al: Clinical criteria for obtaining maxillofacial computed tomographic scans in trauma patients. Plast Reconstr Surg 127:1270-1278, 2011 14. Rhea JT, Novelline RA: How to simplify the CT diagnosis of LeFort fractures. AJR Am J Roentgenol 184:1700-1705, 2005 15. Gordin EA, Daniero JJ, Krein H, et al: Parotid gland trauma. Facial Plast Surg 26:504-510, 2010 16. Escott EJ, Branstetter BF: Incidence and characterization of unifocal mandible fractures on CT. AJNR Am J Neuroradiol 29:890-894, 2008 17. Zayas JO, Feliciano YZ, Hadley CR, et al: Temporal bone trauma and the role of multidetector CT in the emergency department. Radiographics 31:1741-1755, 2011 18. Meriot P, Veillon F, Garcia JF, et al: CT appearances of ossicular injuries. Radiographics 17:1445-1454, 1997 19. Kienstra MA, Van Loveren H: Anterior skull base fractures. Facial Plast Surg 21:180-186, 2005 20. Manson PN, Stanwix MG, Yaremchuk MJ, et al: Frontobasal fractures: Anatomical classification and clinical significance. Plast Reconstr Surg 124:2096-2106, 2009 21. Sun GH, Shoman NM, Samy RN, et al: Analysis of carotid artery injury in patients with basilar skull fractures. Otol Neurotol 32:882-886, 2011 22. Hanson JA, Deliganis AV, Baxter AB, et al: Radiologic and clinical spectrum of occipital condyle fractures: Retrospective review of 107 consecutive fractures in 95 patients. AJR Am J Roentgenol 178:12611268, 2002 23. Feiz-Erfan I, Horn EM, Theodore N, et al: Incidence and pattern of
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direct blunt neurovascular injury associated with trauma to the skull base. J Neurosurg 107:364-369, 2007 Stuhlfaut JW, Barest G, Sakai O, et al: Impact of MDCT angiography on the use of catheter angiography for the assessment of cervical arterial injury after blunt or penetrating trauma. AJR Am J Roentgenol 185: 1063-1068, 2005 Uyeda JW, Anderson SW, Sakai O, et al: CT angiography in trauma. Radiol Clin North Am 48:423-438, ix-x, 2010 Aouad R, Moutran H, Rassi S: Laryngotracheal disruption after blunt neck trauma. Am J Emerg Med 25:1084, 2007 Demetriades D, Velmahos GG, Asensio JA: Cervical pharyngoesophageal and laryngotracheal injuries. World J Surg 25:1044-1048, 2001 Comer BT, Gal TJ: Recognition and management of the spectrum of acute laryngeal trauma. J Emerg Med 2010 January 28 (Epub ahead of print) Sliker CW, Shanmuganathan K, Mirvis SE: Diagnosis of blunt cerebrovascular injuries with 16-MDCT: Accuracy of whole-body MDCT compared with neck MDCT angiography. AJR Am J Roentgenol 190:790799, 2008 Delgado Almandoz JE, Schaefer PW, Kelly HR, et al: Multidetector CT angiography in the evaluation of acute blunt head and neck trauma: A proposed acute craniocervical trauma scoring system. Radiology 254: 236-244, 2010 Kohler R, Vargas MI, Masterson K, et al: CT and MR angiography features of traumatic vascular injuries of the neck. AJR Am J Roentgenol 196:800-809, 2011
329 32. Núñez DB, Torres-León M, Múnera F: Vascular injuries of the neck and thoracic inlet: Helical CT-angiographic correlation. Radiographics 24: 1087-1100, 2004 33. Steenburg SD, Sliker CW, Shanmuganathan K, et al: Imaging evaluation of penetrating neck injuries. Radiographics 30:869-886, 2010 34. Múnera F, Soto JA, Palacio D, et al: Diagnosis of arterial injuries caused by penetrating trauma to the neck: Comparison of helical CT angiography and conventional angiography. Radiology 216:356-362, 2000 35. Inaba K, Munera F, McKenney M, et al: Prospective evaluation of screening multislice helical computed tomographic angiography in the initial evaluation of penetrating neck injuries. J Trauma 61:144-149, 2006 36. Bell RB, Osborn T, Dierks EJ, et al: Management of penetrating neck injuries: A new paradigm for civilian trauma. J Oral Maxillofac Surg 65:691-705, 2007 37. Ginsberg LE, Williams DW 3rd, Mathews VP: CT in penetrating craniocervical injury by wooden foreign bodies: Reminder of a pitfall. AJNR Am J Neuroradiol 14:892-895, 1993 38. Apffelstaedt JP, Müller R: Results of mandatory exploration for penetrating neck trauma. World J Surg 18:917-919, 1994 39. Young CA, Menias CO, Bhalla S, et al: CT features of esophageal emergencies. Radiographics 28:1541-1553, 2008 40. Asensio JA, Berne J, Demetriades D, et al: Penetrating esophageal injuries: Time interval of safety for preoperative evaluation—How long is safe? J Trauma 43:319-324, 1997
T
he American College of Surgeons’ National Trauma Databank of the year 2011 reported 722,824 incidents of trauma during the year 2010.1 Falls contributed to the major mechanism of injury (38.4%), followed by motor vehicle collisions (28.9%). Injuries from mechanisms of being struck (7.5%), cut/pierced (4.7%), or related to firearms (4.5%) were much less common. Injuries to the head and face combined accounted for 59.7% of cases.1 As such, it is apparent that head- and neck-related trauma is a major source of injury in the United States. In the trauma setting, rapid access to imaging is important in making diagnoses and guiding management decisions for the trauma team. In the acute setting, multidetector-row computed tomography (CT) is becoming the imaging modality of choice. This is because of its wide availability throughout most hospitals and its ability to acquire images rapidly. In certain settings, CT angiography (CTA) is being increasingly used to evaluate for trauma-related vascular injuries, as opposed to conventional angiography. Although conventional angiography remains the gold standard for evaluating vascular injury, it is an invasive procedure, which is more time and labor intensive, and is not as widely available as CTA. Magnetic resonance imaging (MRI) and MR angiography are not as commonly used as CT and CTA in the setting of acute trauma because they are more time intensive and not compatible with certain life-support equipment.2 We provide a review of the different types of injuries and their imaging features that may be encountered in the setting of head and neck trauma, with a focus on CT.
Head A noncontrast CT of the head is usually the first imaging modality of choice in the setting of head trauma. Typical imaging protocols when imaging the head should include the skull base through the vertex. At our institution, images of the brain are obtained axially using 5-mm slice thickness, with axial 1.25-mm reconstructions in soft-tissue and bone algorithms. Coronal 5-mm soft-tissue reconstructions are also routinely performed to aid in detection of subtle intracranial hemorrhages.3
Soft-Tissue Injuries Trauma to the head frequently results in superficial soft-tissue injuries, including subcutaneous hematomas and lacerations. The presence of superficial soft-tissue injuries should raise suspicion for underlying fractures or intracranial injuries.
Department of Radiology, Boston Medical Center, Boston University School of Medicine, Boston, MA. Address reprint requests to Rohini N. Nadgir, MD, Department of Radiology, Boston Medical Center, Boston University School of Medicine, 820 Harrison Avenue, FGH Building, 3rd Floor, Boston, MA 02118. E-mail: [email protected]
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Skull Fractures Skull fractures may be linear, comminuted, or depressed. In children, diastatic fractures are more common.4 Three-dimensional (3D) volume-rendered reconstructions of the skull can aid in detection of skull fractures in the axial plane, particularly in pediatric patients. The presence of any skull fractures should always lead to closer evaluation for intracranial injuries such as intracranial hemorrhage or contusions. Attention should be given to the intracranial region directly beneath the fracture site and the region opposite the fracture (contrecoup injury).
Orbits Traumatic orbital injuries account for up to 3% of all emergency room visits in the United States, and are most commonly due to motor vehicle collisions and sports-related injuries.5 CT is the imaging modality of choice to evaluate for orbital injury. Optimal protocols for CT orbital imaging should include thin-section axial images and multiplanar reformats in soft-tissue and bone algorithms. At our institution, 1.25-mm axial images are obtained through the orbits, with 1.5-mm/1.5-mm coronal and sagittal reconstructions in soft-tissue and bone algorithms.
Fractures Fractures of the orbit commonly involve one (48%) or two (30%) orbital walls.6 The orbital floor and medial wall are the weakest structures and are therefore the most susceptible to injury.6 Orbital wall fractures may occur in conjunction with other facial fractures, such as zygomaticomaxillary complex (ZMC), nasoethmoid, frontal bone, and LeFort fractures.6,7 A traumatic force directed toward the eye can cause increased intraorbital pressure, which transmits outwardly along the orbital walls. This pressure leads to a blow-out type orbital fracture (Fig. 1). The orbital floor and medial walls are the most susceptible to blow-out fractures, sparing the orbital rim.8 High-energy trauma can rarely lead to fractures at the level of the orbital apex, the deepest portion of the orbit. Fractures at this location typically require urgent surgical treatment because of the high incidence of associated optic nerve injury.
Soft-Tissue Injuries Acute bony orbital injuries are often accompanied by periorbital soft-tissue swelling/hematoma,6 and such a finding should prompt a thorough evaluation for bony injury. Fractures of the orbital floor may affect the infraorbital nerve as it passes through the infraorbital canal. Involvement of this canal should raise suspicion for nerve injury and should be evaluated clinically. In the setting of blow-out fractures, the fracture mechanism allows for the possibility of extraocular muscle entrapment. Although muscle entrapment remains a clinical diagnosis, certain imaging features may suggest entrapment, including displacement of the extraocular muscle, penetration of muscle by bone fragment or foreign body material, or an abnormal contour of the extraocular muscle. Optic nerve injuries are rare, seen in up to 2% of orbital
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321 CT is highly suggestive of globe rupture (Fig. 2). However, widening of the anterior chamber, secondary to decreased intraocular pressure, may be the only sign of globe rupture in more subtle cases.9 Other indirect signs of possible globe rupture include the presence of intraocular air or foreign bodies (Fig. 3). Traumatic eye injuries can also disrupt the internal structures of the globe. The lens can be dislocated partially or completely and can be seen layering dependently in the globe on CT. The retina can also become detached as a result of trauma. The retina is firmly fixed along its anterior and posterior attachments, while it is loosely attached elsewhere. Therefore, the subretinal fluid in retinal detachment typically appears V shaped, with the apex at the optic disc.5 Choroidal hemorrhages are typically crescentic or parallel in configuration and characteristically spare the region of the optic disc, at the posterior third of the globe, because of the anchoring effect of ciliary vascular and neuronal tissues.10 Focal subhyaloid hemorrhages may rarely be seen in the setting of intracranial subarachnoid hemorrhage, often referred to as Terson syndrome.11 Globe trauma can disrupt the vasculature without affecting the structural integrity of the globe, which can lead to hemorrhage within the globe. Hemorrhage within the anterior chamber (hyphema) is usually apparent clinically; however, vitreous hemorrhage may not be as obvious clinically and may be more readily appreciable on imaging. On CT, vitreous hemorrhage appears as focal or diffuse hyperdensity within the vitreous body. Carotid– cavernous fistulas may form as a result of head trauma. Carotid– cavernous fistulas are clinically characterized as diplopia, proptosis, and chemosis, which can occur in the post-traumatic setting. A traumatic tear in the cavernous segment of the internal carotid artery (ICA) creates a fistulous connection with the cavernous sinus, causing increased cavernous sinus pressure. This increased pressure can transmit to the ophthalmic vein, leading to unilateral or bilateral dilation, which can be appreciated on noncontrast CT. On CTA, the typical findings may include an asymmetrically enlarged ipsilateral cavernous sinus of similar attenuation to opacified arterial structures, enlargement of the dural venous sinuses, enlargement and tortuosity of the superior ophthalmic vein, enlargement of the extraocular muscles, proptosis, and subchoroidal effusions.12
Midface Facial injuries are seen in up to 25% of trauma cases, and ⬎150,000 patients present to the emergency room with facial trauma annually, most commonly in the setting of motor vehicle collisions.13 Optimal protocols for CT imaging of the facial bones should include thin-section axial images and multiplanar reformats in soft-tissue and bone algorithms. At our institution, 1.25-mm axial images are obtained through the facial bones, with 1.5-mm/1.5-mm coronal and sagittal reconstructions in soft-tissue and bone algorithms.
Figure 1 A 45-year-old man with an orbital blow-out fracture after assault. (A) Coronal computed tomographic (CT) image demonstrates depressed defect of the left orbital floor (white arrow) with associated hemorrhage and orbital gas present in the inferior orbit (black arrow). Note relative enlargement of the inferior rectus muscle, which suggests intramuscular hematoma. (B) Sagittal CT image shows the depressed fracture fragment (white arrow) and preservation of the orbital rim (black arrow). fractures,6 but should be suspected when fractures are seen extending into the optic canal. Stretching of the optic nerve may also be seen in the setting of traumatic proptosis, and it requires urgent ophthalmologic evaluation owing to a high risk of development of blindness. Orbital trauma can also lead to various injuries of the globe, seen in up to 5% of cases of isolated orbital fractures.6 Blunt or penetrating trauma can disrupt the normal spherical shape of the globe, leading to globe rupture, which is a major cause of blindness.5 An abnormal contour of the globe on
Figure 2 A 61-year-old woman who sustained head trauma and globe rupture. Axial CT image shows enlargement and deformity of the left globe contours and vitreous hemorrhage.
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arch, lateral orbital wall, anterior maxillary wall, and posterolateral maxillary wall (Fig. 4). The degree of displacement or comminution of the fracture fragments may affect surgical management. Orbital floor fractures are present in up to 44% of ZMC fractures.7,8
LeFort Fractures
Figure 3 A 37-year-old woman after fall. Coronal CT image shows extensive left periorbital swelling and punctate radiopaque foreign body material within the left globe (black arrow), indicating penetrating injury and violation of the globe. Note otherwise preserved morphology of globe contours.
When needed, 3D volume-rendered reconstructions are obtained to aid in fracture analysis and surgical planning.
Frontal Sinus Fractures Frontal sinus fractures account for 5%-15% of maxillofacial fractures.8 The frontal bone is structurally among the strongest of the facial bones and requires a high-energy force to cause a fracture.8 The frontal sinus consists of anterior and posterior tables (or walls). Anterior table fractures are usually managed conservatively, especially for nondisplaced fractures. Displaced anterior table fractures may lead to cosmetic deformities, necessitating surgical repair.8 Posterior table fractures are treated more aggressively because of the potential for intracranial violation. Nondisplaced fractures of the posterior table may still be treated conservatively with close imaging follow-up, but comminuted or displaced posterior fractures warrant surgical exploration owing to the increased risk of intracranial complications.8 As such, imaging evaluation of frontal sinus fractures should identify involvement of the anterior table, posterior table, or both, and displacement of fracture components should be characterized. With posterior table fractures, a thorough evaluation for signs of dural violation, including hemorrhage or pneumocephalus, is necessary. Long-term complications of frontal sinus fractures can include formation of mucoceles and mucopyoceles. These complications are more common when the fracture involves the nasofrontal duct, which can lead to obstruction of frontal sinus outflow. Other complications can also include osteomyelitis and abscess formation in the epidural or subdural spaces.8
Naso-orbitoethmoid (NOE) Fractures NOE fractures involve the nasal bone, medial orbital wall, and ethmoid bone. NOE fractures typically require higher energy forces compared with isolated nasal bone fractures, and are usually characterized based on the degree of comminution at the attachment of the medial canthus, as well as the integrity of the medial canthal tendon. The degree of bony injury is important to note for the surgeons because it may affect their approach to surgical management. NOE fractures are commonly associated with injuries of the cribriform plate, nasofrontal duct, and globe.7,8
The LeFort classification describes the various complex facial fracture patterns that cause separation of the maxilla from the skull base. LeFort fractures are seen in up to 26% of facial fractures.7,8,14 In the setting of complex facial injuries, certain fracture patterns may help characterize LeFort fracture types.14 All LeFort fracture types involve the pterygoid process. LeFort I fractures are the only type to involve the anterolateral margin of the nasal fossa. LeFort II fractures are the only type to involve the inferior orbital rim. LeFort III fractures are the only type to involve the zygomatic arch. These unique patterns can be used to distinguish between the different LeFort fractures. When evaluating for LeFort fractures, the clinician and radiologist should be aware that the different types of LeFort fractures can occur synchronously and may also occur in conjunction with other types of facial fractures, such as ZMC and NOE injuries. Additionally, LeFort fractures do not always occur symmetrically (Fig.5).
Parotid Gland Injuries The parotid glands are rarely injured in blunt and penetrating head trauma.15 The bulk of the parotid gland lies over the mandibular ramus, posterior to the masseter muscle. The parotid duct (Stensen’s duct) courses anteriorly, superficial to the masseter muscle. In the setting of trauma, the superficial portion of the gland is more susceptible to injury, and the parotid duct is especially vulnerable owing to its superficial course. Parotid ductal injury should be suspected when lacerations or penetrating injuries occur along the path of the duct. Other important structures that may be affected in conjunction with parotid gland injuries include trauma to the facial nerve, facial artery, and retromandibular vein.15 When parotid gland injuries involve the duct, complications rates can be as high as 80% with nonsurgical management.15 Late complications of parotid gland injuries can include external parotid fistulas, ductal strictures, and sialocele formation (Fig. 6). External parotid fistulas can develop within the first week after injury, and they typically present as clear secretions that occur with mastication. Sialoceles develop more slowly, typically up to two weeks after the injury. On imaging, they can be difficult to distinguish from hematoma or seroma. Gustatory lacrimation (tear formation with salivation) is a rare, but troublesome, complication that can occur after facial nerve injury because of aberrant regeneration of facial nerve fibers toward the pterygopalatine fossa to innervate the lacrimal gland.15
Mandible The mandible has been described as the most commonly fractured facial bone in the setting of motor vehicle collisions.16 With its articulation at the skull base, the mandible is commonly thought of as a closed ring. Hence, the presence of a fracture should raise suspicion for a second fracture. However, because the mandible is not completely fixed at the temporomandibular joint, unifocal fractures do occur frequently.16 The most common locations of mandibular fractures include the angle (30%), followed by the body (26%), parasymphyseal region (16%), and condyle (12%).16 When mandibular fractures are identified, the degree of displacement or comminution should be evaluated (Fig. 7). Extension of the fracture through the mandibular canal should also be noted, as it may be an indication of alveolar nerve injury. In addition, the presence of any associated tooth fractures or tooth loosening should be thoroughly evaluated, as these are susceptible to aspiration, particularly in a patient who is unconscious.
ZMC Fractures In the setting of blunt facial trauma, ZMC fractures are the most common type of facial fractures.7,8 ZMC fractures are considered quadripod fractures, involving break points around the 4 sutural connections of the zygoma: the zygomaticofrontal, zygomaticotemporal, zygomaticomaxillary, and zygomaticosphenoid sutures. These correspond to fractures involving the zygomatic
Temporal Bone The temporal bone is divided into five segments: squamous, mastoid, petrous, tympanic, and styloid. Several major vessels course through the temporal bone, including the ICA, middle meningeal artery, sigmoid sinus, and
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Figure 5 A 50-year-old male bicyclist who was struck by a car, with multiple LeFort injuries. 3D volume-rendered image shows bilateral LeFort I (widely spaced dots), bilateral LeFort II (less widely spaced dots), and unilateral LeFort III (narrowly spaced dots) injuries. Note associated zygomaticomaxillary complex fracture component (arrow), as well as bilateral mandibular fractures. jugular bulb. The temporal bone also contains the inner ear structures (cochlea, semicircular canals, and internal auditory canal), as well as the middle ear cavity, which houses the ossicles. Because of the fine bony anatomy of the temporal bone, optimal CT imaging protocols should include thin-section (preferably submillimeter) axial images with multiplanar reformats in bone algorithms. Helically acquired data can provide overlapping thin-section images for greater anatomic detail; however, in the trauma setting, thin-section axially acquired data from noncontrast head CT can provide satisfactory anatomic detail without exposing the patient to additional radiation.17 In addition, CT angiography or CT venography should be considered when there is suspicion for associated arterial or venous sinus injury.
Fractures Temporal bone injury can occur in up to 22% of patients with skull fractures.17 Common causes include motor vehicle collisions, falls, and assaults. In the setting of trauma, the most commonly injured portions of the temporal bone include the petrous and mastoid segments. Fractures are traditionally classified as transverse (perpendicular to the axis of the temporal bone)
Figure 4 A 59-year-old man with zygomaticomaxillary complex fracture after a fall. (A) Axial CT image shows comminuted disruption of the anterior (white arrow) and posterolateral (black arrow) walls of the left maxillary sinus. There is depressed deformity of the zygomatic arch (arrowhead). Note disruption of the infraorbital nerve canal. (B) More superiorly, there is comminuted disruption of the lateral orbital wall on the same side (white arrow). (C) 3D volume-rendered image shows the anterior maxillary (black arrows), lateral orbital wall (white arrow), and zygomatic arch (arrowhead) fractures.
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poral bone.17 Occult nondisplaced temporal bone fracture should be considered when these findings are noted in the trauma setting.
Ossicular Injuries Hearing loss as a result of trauma can be due to laceration of the tympanic membrane, hemotympanum, or injury to the ossicles. Ossicular injuries can be seen in up to 32% of temporal bone traumas.18 Dislocation of the ossicles is a more common manifestation of ossicular injuries than fractures. The malleus and stapes have firm attachments, whereas the incus is less firmly suspended between the other two; therefore, the incus is most prone to dislocation.18 Incudomalleolar joint separation has a typical appearance on axial CT images, with a displaced “ice cream scoop” (malleolar head) from the “ice cream cone” (short process of incus).
Figure 6 A 27-year-old man with parotid duct injury after assault. (A) Axial CT image shows edema and soft-tissue stranding overlying the expected course of Stenson’s duct (arrow). Surgical exploration with duct repair and stent placement was performed subsequently. (B) Axial CT image a year later shows development of dilated duct (arrow) because of the stricture at the outlet of Stenson’s duct, despite surgical intervention.
or longitudinal (parallel to the axis of the temporal bone). Longitudinal fractures are more common, seen in approximately 70%-90% of cases.17 Temporal bone fractures can also be categorized as otic capsule violating or sparing. Otic capsule–violating fractures involve injury to inner ear structures and are associated with more complications, such as facial paralysis, cerebrospinal fluid (CSF) leak, or profound hearing loss (Fig. 8).17 Temporal bone fractures that involve the carotid canal may have associated vascular injuries of the petrous segment of the ICA, such as dissection, pseudoaneurysm, transection, or occlusion. Such vascular complications can be seen in up to 11% of fractures that involve the carotid canal.17 Additionally, given the proximity of the sigmoid sinus to the temporal bone, a fracture can also lead to venous injury, with resulting thrombosis (Fig. 9). Some temporal bone fractures may be radiographically occult and only demonstrate secondary signs of fracture. These signs may include opacification of the mastoid air cells or middle ear, air–fluid levels in the sphenoid sinus, and pneumocephalus or extra-axial hemorrhage adjacent to the tem-
Figure 7 A 40-year-old woman with mandibular fracture after assault. (A) Axial CT image shows unilateral displaced fracture at the posterior body of the mandible on the left. Note disruption of the mandibular canal (black arrow). (B) 3D volume-rendered image shows degree of override of the fracture fragments, which aided in the surgical planning approach.
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Skull Base Frontobasal Injuries Frontobasal (anterior skull base) injuries represent 3%-5% of all craniomaxillofacial fractures, and are usually the result of blunt trauma, motor vehicle collisions, or falls.19,20 These fractures can involve isolated linear fractures of the cranial base (type 1), linear fractures of the cranial base and frontal bone (type 2), or comminuted fracture of the entire frontal bone segment and orbital roof (type 3). Frontobasal injuries are usually associated with other facial fractures, most commonly NOE fractures, followed by LeFort Type III fractures.19,20 Frontobasal injuries are typically the result of high-energy impact and are therefore prone to more complications. Violation of the dura can lead to a dural fistula, with complications including CSF leak, rhinorrhea, or pneumocephalus. These complications increase the risk of meningitis, especially in the setting of persistent CSF leak lasting ⬎2 weeks.19,20
Basilar Skull Injuries Basilar skull fractures can be seen in up to 30% of head injuries.21 Unilateral and bilateral occipital condylar fractures are seen in high-energy impact injuries and can be associated with additional brain and cervical spine injuries. These are often associated with ligamentous soft-tissue injury demonstrable by MRI and require surgical stabilization.22 Additional vascular injuries including dissections and pseudoaneurysms of the internal carotid and vertebral arteries, as well as dural arteriovenous fistulas (AVF), can occur.23
Neck Injury to the soft-tissue neck can occur with blunt or penetrating trauma. When there is suspicion for vascular injury, CTA should be considered as the initial imaging modality for diagnosis and guiding management.24 CTA can be timed for arterial or venous phases depending on clinical suspicion. After timed bolus contrast injection, helically acquired submillimeter axial images through the neck should be obtained and evaluated in conjunction with maximum intensity projection reformations in axial, coronal, and sagittal planes. At our institution, we obtain 0.625-mm axial images from the aortic
Figure 8 A 20-year-old woman involved in rollover motor vehicle collision with temporal bone fracture. Axial CT image shows transversely oriented defect through the otic capsule structures including the vestibule and vestibular aqueduct (white arrow). Note associated air, pneumolabyrinth, within the basal turn of the cochlea (black arrow).
Figure 9 A 21-year-old woman involved in motor vehicle collision with temporal bone fracture and venous thrombosis. (A) Axial CT image shows longitudinally oriented fracture through the mastoid (black arrows) and petrous segments of the temporal bone extending to involve the carotid canal (large white arrow). Note air adjacent to the carotid canal and within middle cranial fossa. There is diastasis of the occipitomastoid suture (arrowhead) with tiny pockets of gas at the expected location of the sigmoid sinus (small white arrow). (B) Computed tomography angiographic (CTA) image demonstrates patency of the left internal carotid artery (ICA) (not shown), but confirms presence of filling defect within the left sigmoid sinus (black arrow), consistent with nonocclusive thrombus.
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E.K. Sung, R.N. Nadgir, and O. Sakai With more severe injury, a dissection can occur where the intima is torn away from the other layers of the vessel. This leads to a raised intimal flap, which typically appears as a linear intraluminal filling defect. With even more severe injury, an intramural hematoma may develop, which can appear as eccentric or circumferential mural thickening. On imaging, the arterial lumen will be narrowed, but the overall diameter of the injured vessel may be increased. If large enough, this can result in complete occlusion of the vessel (Fig. 11).12,29,31 In the setting of blunt trauma, arterial dissection is the most common injury.31 Pseudoaneurysms can also develop as a result of blunt vascular injury. They are not true aneurysms in that they do not contain the normal layers of an artery. Rather, the extravasating blood from a focal injury in the artery becomes locally contained by the surrounding perivascular connective tis-
Figure 10 A 42-year-old construction worker (male) after a beam fell on his neck. Axial CT image shows acute fracture of the tracheal cartilage (arrow). Adjacent air in the overlying soft tissues is strongly suggestive of associated tracheal injury, although the precise focus of injury could not be identified on imaging.
arch to the level of circle of Willis with maximum intensity projection images (5-mm thickness and 2-mm interval) in all three planes.25
Blunt Soft-Tissue Neck Injury Injury to the soft-tissue structures of the neck, including the pharynx, esophagus, larynx, and trachea, are extremely rare in the setting of blunt trauma.26,27 The larynx and trachea are more susceptible to injury owing to their superficial positioning. Blunt laryngotracheal injuries can occur with high-impact direct blow injuries or crush injuries.27 Although penetrating laryngotracheal injuries are more frequent and significant, blunt laryngotracheal injuries are less readily apparent clinically and may require imaging for diagnosis.28 Therefore, in the setting of blunt neck trauma, the radiologist should thoroughly assess the larynx and trachea and look for secondary signs of laryngotracheal injury such as unexplained subcutaneous gas, thyroid or cricoid cartilage fractures, or adjacent hematomas (Fig. 10). Care should be taken to distinguish subcutaneous gas in the neck related to laryngotracheal injury from gas tracking superiorly from a pneumothorax or pneumomediastinum. The accurate identification of laryngotracheal injuries is extremely important because of the potential for life-threatening airway compromise.26-28
Blunt Cereberovascular Injury The prevalence of cerebrovascular injury among all patients with blunt trauma can be up to 1.6%.12 The major cause of morbidity and mortality related to blunt cerebrovascular injury is brain infarction. Morbidity and mortality rates for blunt carotid artery injury range from 32% to 67% and 17% to 38%, respectively.12,29 With blunt vertebral artery injury, the morbidity and mortality rates are lower, ranging from 14% to 24% and 8% to 18%, respectively.12,29 Although traumatic arterial injuries can occur without fractures, the risk is significantly increased with the presence of any major facial, skull, or cervical spine fracture, as well as in the setting of a high-impact trauma.30 The risks of arterial injury are highest in patients with cervical interfacetal subluxations, followed by fractures that extend into foramen transversarium and the ICA canal.30 For these reasons, CTA evaluation for arterial injury is recommended in the setting of high-impact mechanisms of injury, regardless of the presence of a fracture, low-impact mechanisms of injury if there is a fracture reaching the expected location of an arterial structure, or presence of cervical interfacetal subluxation. The degree of injury to an artery can be variable, and includes intimal injury, pseudoaneurysm, occlusion, or complete arterial transection. Formation of AVF can also occur. Minimal intimal injury will typically appear as areas of nonstenotic luminal irregularity, and can be difficult to distinguish from vasospasm.
Figure 11 A teenage boy, choked, with ICA dissection. (A) CTA performed because of the trauma mechanism shows abrupt tapered occlusion of the ICA (black arrow), consistent with dissection on sagittal maximum intensity projection (MIP) reformats. (B) Axial T2-fat suppressed image from magnetic resonance imaging performed for left-sided weakness after the event shows intramural and extramural hematoma (white arrow), confirming dissection. Diffusion images confirmed cerebral infarct in the right middle cerebral artery distribution (not shown).
CT imaging in head and neck trauma sue. Therefore, pseudoaneurysms typically appear as eccentric outpouchings of contrast material on imaging, and can vary considerably in shape and size. In comparison, complete transection of an artery will cause active hemorrhage, which appears as an irregular collection of extravascular contrast, typically surrounding or adjacent to the injured vessel.12,29 Arterial injury can also lead to the formation of an AVF. On CTA, venous structures near the AVF will demonstrate early enhancement during the arterial phase, similar in density to adjacent arterial structures, and the fistulous connection may be visualized. However, findings are often subtle, and suboptimal arterial-phase imaging techniques can make it difficult to
327 visualize the early enhancement of the veins.12,29 When clinical suspicion is high, conventional angiography may follow for clarification and/or treatment purposes.
Penetrating Trauma Penetrating injuries of the neck can involve multiple structures including arteries, veins, esophagus, and trachea (Fig. 12). Owing to the mechanism, vascular injuries of the neck occur more commonly after penetrating trauma compared with blunt trauma.32 As such, the morbidity from arterial injuries
Figure 12 A 31-year-old man after nail-gun accident. (A) Sagittal MIP reformat from CTA shows penetrating object violating trachea and likely involving esophagus based on trajectory. (B) Coronal MIP reformat shows nail abutting the brachiocephalic artery (arrow), but owing to beam-hardening artifact, focal vessel injury could not be entirely excluded. (C) Conventional angiogram confirms patency of the brachiocephalic artery, with slight focal extrinsic deformation along the medial wall of the vessel by the nail (arrow).
E.K. Sung, R.N. Nadgir, and O. Sakai
328 is usually related to neurologic damage from strokes, and mortality rates can be as high as 10%.33,34 In the setting of penetrating neck trauma, the neck is divided into three zones: zone I extends from the sternal notch and clavicles to the cricoid cartilage; zone II extends from the cricoid cartilage to the angle of the mandible; and zone III extends from the mandible to the base of the skull. The management of penetrating neck injuries has been controversial, with traditional guidelines recommending surgical exploration for any penetrating injuries in zone II and reserving nonsurgical evaluation, including angiography, endoscopy, and laryngoscopy, for injuries in zones I and III because of the difficulty in accessing these regions surgically. However, in recent years, CT and CTA have become increasingly used as methods for the initial evaluation of penetrating neck injuries in all zones, which allows for even more selective surgical exploration.33-36 In the imaging evaluation of penetrating neck trauma, determining the trajectory of the penetrating object can be of great importance in identifying the structures at risk for injury. Depending on the nature of the material, penetrating objects have variable densities on CT scans. Metallic densities (ie, bullet fragments) can contribute to significant beam-hardening artifact, which can limit evaluation of adjacent structures. In these settings, it is imperative to evaluate for the presence of metallic material within critical structures including the orbit and spinal canal, as these are contraindications to further imaging by MRI. The radiologist should be aware that woodenpenetrating objects may be difficult to distinguish from air on CT, and evaluation should include assessment at wider window settings to increase conspicuity of the object trajectory.37 Up to 25% of penetrating neck injuries can result in arterial injuries, with the carotid arteries involved more than the vertebral arteries, owing to their superficial location.33 Similar to blunt trauma, arterial injury from penetrating trauma can include intimal injury, dissection, partial or complete occlusion, pseudoaneurysm, or AVF formation. However, when compared with blunt trauma, dissections occur less frequently and the incidence of arterial occlusion and transection is higher in penetrating injuries.31,33 For the detection of arterial injuries in the neck, CTA has been shown to have a sensitivity and specificity ⬎90%.33,34 Venous injuries are more common in the setting of penetrating injuries compared with blunt trauma.31 Injuries to the neck veins have been seen in up to 51% of penetrating neck injuries; however, they are more commonly clinically silent when compared with arterial injuries.38 Venous injuries often present as occlusions or pseudoaneurysms.31 In addition, a concurrent injury to a vein and artery in the same region can lead to the development of an AVF. Esophageal injuries are uncommon and seen in up to 6% of patients with penetrating trauma.27,33,36,39 On imaging, if the suspected penetration tract is far from the esophagus, esophageal injury can be excluded. However, pockets of gas along the tract in the expected vicinity of the esophagus should raise suspicion for injury. This should not be confused with a tracheal diverticulum, which is a common normal anatomic variant, seen as a focal collection of gas in the tracheoesophageal groove region on the right. When esophageal injury is suspected, direct visualization with endoscopy is necessary. Alternatively, a barium-swallow examination may be considered, although it may be technically difficult in an acutely injured patient. A delayed diagnosis of an esophageal injury can lead to complications, including abscess formation, mediastinitis, and sepsis, with mortality rates as high as 20%.27,33,36,40 Laryngeal and tracheal injuries are also uncommon, seen in 2%-7% of patients with penetrating neck trauma.27,33,36 However, the potential for this injury should always be considered in the setting of penetrating neck injuries because of the risk of life-threatening airway compromise. Evaluation for laryngotracheal injuries should be based on clinical assessment, imaging findings, and endoscopy. Similar to esophageal injuries, the presence of extraluminal gas near the larynx or trachea should raise suspicion for an airway injury. Long-term complications of tracheolaryngeal injury can include dysphonia, stenosis, or dysphagia.27,33
Conclusions Traumatic injuries to the head and neck and resulting complications are a major cause of morbidity and mortality, necessitating rapid clinical and
radiologic assessment. In the acute setting, CT is becoming the imaging modality of choice. The role of the radiologist is to recommend the appropriate imaging protocols to best evaluate the region of interest and to identify the many different patterns of bone and soft-tissue injuries in these regions. In the imaging evaluation of patients with potential traumatic head and neck injuries, the radiologist should be aware of the acute imaging findings of these injuries and have a thorough understanding of potential short-term and long-term complications.
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