Disclosure
Background: Postacceleration injury, motor vehicular collisions, and violent crimes result in a myriad of orbital and midfacial fractures. Along the visual pathways, trauma is divided into 4 major locations: intraocular, intraorbital, intracanalicular, and intracranial. The following discussion focuses on patterns of orbital injury stereotyped as blow-out or blow-in fractures, with peripheral consideration of Tripod and Le Fort fractures. In 1901, Renée Le Fort provided the earliest classification system of maxillary fractures. His model described "great lines of weakness in the face" caused by low-velocity impact forces directed against cadaver skulls. A discussion of fractures of the maxilla would not be complete without a description of Le Fort's work. The Le Fort I fracture, or transverse fracture, extends through the base of the maxillary sinuses above the teeth apices, essentially separating the alveolar processes, palate, and pterygoid processes from the facial structures above. This transverse fracture across the entire lower maxilla separates the alveolus as a mobile unit from the rest of the midface. Fracture dislocations of segments of the alveolus may be associated with this fracture. With high-energy injuries, the palate may be split in the midline in addition to the Le Fort I fracture. A pyramidal fracture of the maxilla is synonymous with a Le Fort II fracture. This fracture pattern begins laterally, similar to a Le Fort I, but it medially diverges in a superior direction to include part of the medial orbit as well as the nose. The fracture extending across the nose may be variable, involving only the nasal cartilage or as extensive as to separate the nasofrontal suture. The fracture extends diagonally from the pterygoid plates through the maxilla to the inferior orbital rim and up the medial wall of the orbit to the nose. This separates the maxillary alveolus, medial wall of the orbit, and nose into separate pieces. A Le Fort III fracture, or craniofacial disjunction, denotes a complete separation of the midface or facial bones from the cranium. This fracture transverses the zygomaticofrontal suture, continues through the floor of the orbit, and finally passes through the nasofrontal suture. The bones of the orbit are separated through the lateral wall, floor, and medial wall. This fracture rarely results in a single segment of bone; more commonly, the break is comminuted, with varying combinations of zygomatic, nasoethmoid, and orbital fractures. The fractures may not be symmetric on both sides, and minimal mobility may be present. Pathophysiology: Blow-out fractures Blow-out fractures are produced by a nonpenetrating force to the anterior periorbital region that compresses orbital contents and causes a sudden increase in intraorbital pressure. This mechanism results in the outward transmission of force to the weakest segment of the orbit along the vector of injury. Pure forms of blow-out and blow-in fractures refer to the internal orbital skeleton, with the orbital rim remaining intact. Of course, with non-pure complex orbital fractures, the rim can also be fractured. It is not surprising that blow-out fractures are most commonly directed inferiorly, given that the orbital floor is the weakest portion of the orbit. In 1957, Smith and Reagan showed in cadaver experiments that these fractures typically occur in the middle third of the orbital floor. The infraorbital nerve normally traverses this region via the inferior orbital canal and thus is prone to injury there. With inferior displacement of the floor fracture fragment, intraorbital soft-tissues, such as fat and even extraocular muscle, not infrequently herniate into the maxillary antrum. Entrapment of the inferior rectus muscle is a serious possible complication to be anticipated. Pelton and other authors have proposed that the soft-tissue glove of orbital fat, ligamentous and fascial tissue, and extraocular muscles protects the globe by absorbing considerable energy during impact. Blow-out fractures involving the delicate medial orbital wall (lamina papyracea) do occur in isolation, but they most frequently occur in combination with orbital floor fractures. Although the lamina papyracea is truly thinner than the orbital floor, it is actually buttressed by perpendicular elements of the ethmoid sinus bony lattice and thus fractures less often. Orbital emphysema is most commonly seen with fractures of the medial wall. Orbital contents can uncommonly prolapse into the ethmoid sinus if the fracture is large enough, though entrapment of the medial rectus muscle is rare. Should the trochlea of the orbit be involved, the superior rectus muscle would be compromised. Rare superior orbital blow-out fractures involve the orbital roof, with an intact orbital rim. Fracture fragments are then be displaced into the frontal sinus or even into the anterior cranial fossa. Blow-in fractures Orbital blow-in fractures are produced by blunt trauma, usually trauma against the frontal bone or the maxilla, with resultant transmission of energy towards the orbital roof or floor, respectively. The fracture fragments are characteristically displaced toward the orbital space. Pure forms of blow-out and blow-in fractures refer to the internal orbital skeleton, with the orbital rim remaining intact. Of course, with injuries that are not purely complex orbital fractures, the rim can also be fractured. The posterior portion of the orbital roof near the optic canal and superior orbital fissure is especially weak. The optic nerve is vulnerable at this fracture point. Inwardly displaced orbital roof fragments can impress into the superior rectus and levator palpebrae muscles. Of interest, 14-29% of reported orbital roof blow-in fractures are associated with an intraocular (globe) injury. In the skull cavity, associated injuries include frontal lobe contusion, dural tear, and even formation of acquired encephalocele in the fracture defect. Blunt trauma to the anterior maxilla is a typical cause of inferior blow-in fractures of the orbit. Upwardly displaced bone fragments may impinge the inferior rectus and inferior oblique muscles. Medial blow-in fractures have been described, typically resulting from a direct blow and fragmenting the nasal bones and medial orbital wall. Other fractures Peripheral to the above discussion of orbital fractures are Le Fort fractures and fractures of the zygomaxillary complex (ZMC). Le Fort fractures traverse the bilateral maxilla in a predominantly horizontal plane. Type I Le Fort injury spares the orbit, whereas Le Fort II and Le Fort III fractures are both symmetric orbitomaxillary fractures. These fractures extend posteriorly, typically involving the pterygoid plates and pterygomaxillary fossa. Le Fort II fractures converge medially along bilateral zygomaxillary sutures toward the medial aspect of respective orbits. There, the nasal bones, lacrimal bone, and frontal process of the maxilla are fractured. A pure tripod fracture entails separation of the zygoma from the face. The zygomatic arch is disrupted (laterally), and there is simultaneous disruption at or near the sutures of the zygoma with the frontal and maxillary bones. Fractures involving the orbital apex are associated with anterior skull base fractures. By anatomic location, the optic nerve is particularly prone to injury there. Frequency:
Mortality/Morbidity: The evolution is good in general. Few sequelae are noted in 25% cases. A fundamental factor is the precocity of diagnosis and treatment and multidisciplinary collaboration, which permit adapted treatment with few sequelae. Race: Racial differences are not statistically significant. Sex: Men are at higher risk for eye injuries than women because of their increased incidence of trauma. Approximately 86% of patients are men. Age: About 78% of cases involve young adults. The age distribution of patients with orbital fractures is as follows: 0-10 years, 7.04%; 10.1-20.0 years, 12.68%; 20.1-30.0 years, 28.17%; 30.1-40.0 years, 21.13%; 40.1-50.0 years, 14.09%; 50.1-60.0 years, 9.86%; 60.1-70.0 years, 2.82%; and 70.1-80.0 years, 4.23%. Anatomy: The orbit (see Image 1) is a conical structure, with its base facing anterolaterally and its apex originating medially as the inlet of all vital neural and vascular structures via the optic foramen, superior orbital fissure, and inferior orbital fissure. The anterior rim of the bony orbit, the orbital rim, is formed by orbital processes from the maxilla, zygoma, and frontal bone. The orbit is composed of 7 bones of the skull, with the optic foramen and superior and inferior orbital fissures primarily marginated by the sphenoid bone. Just superior to the orbital roof (frontal bone) is the frontal sinus. The orbital roof is immediately above the ipsilateral maxillary sinus. The ethmoid sinus parallels the medial orbital wall (lamina papyracea). The anterior aspect of the medial orbital wall is formed by the lacrimal bone, which encases the nasolacrimal duct. The lateral orbital wall is not bordered by a sinus. The zygoma forms the thick lateral wall of the orbit, with the zygomaticofrontal suture superiorly and the zygomaxillary suture inferiorly. Not directly associated with the orbit, the temporal process of the zygoma extends laterally to form the anterior half of the zygomatic arch. Aside from the globe itself, major intraorbital soft-tissue components include the extraocular muscles, retro-orbital fat, optic nerve, and superior ophthalmic vein. Clinical Details: About 17% of patients present with persistent headache, frontal pain, and concentration difficulties. Of these patients, 75% have sustained combined naso-orbitoethmoidal (NOE) and craniocerebral injury. The severity of the pain is characterized as low or moderate 75% of cases. In the other 25%, the pain is associated with concentration difficulties, and medication is regularly required. Approximately 46.5% of patients complain of a loss of smell. In a sample patient population, low-degree derangement was found in 7% of patients; moderate derangement, in 14%; and severe derangement, in 25.4%. For the clinical evaluation, it is important: (1) to be familiar with the complex anatomy of the orbit and relative soft tissues, as displayed on CT scans and MRIs in multiple planes; (2) to learn to identify common acute emergent lesions; (3) to be familiar with the plain radiographic and CT appearances of traumatic fractures of the orbit; and (4) to be able to characterize fractures based on clinical classification systems (eg, Le Fort classification). Preferred Examination: Of all radiologic modalities, CT with a section thickness of 3 mm or less best illustrates fine bony structures of the midface and orbits. Limitations of Techniques: Please see CAT Scan below.
Orbit, Infection
Choroid eye tear
Findings: Orbital radiography (see Image 2) should include several views to clearly depict the various parts of the eye without obstruction. Images of the unaffected eye may also be obtained to compare its shapes and structures with those of the affected eye. Optimally, orbital plain radiography should include the acquisition of direct frontal (posteroanterior [PA] or anteroposterior [AP]), Caldwell, Waters, Towne, and lateral views. That is, views may include the following: side (lateral, from both sides), back to front (PA), and base views. Also, an image from the center to 1 outside edge (half-axial projection) and projections of the optical canal may be useful. For all of these views, the patient may be seated upright or lying down. Visualization of a displaced bone fragment is ideal. As seen in orbital-floor fractures, this finding is commonly referred to as the trap-door sign. The floor fragment typically remains attached medially, similar to a hinge, such that the fragment has a characteristic lateral sloping. Often, the entire floor fragment can be depressed into the subjacent maxillary sinus. If mildly displaced, it may lie parallel (inferior) to its original position. Depending on orientation, the depressed floor fragment can be seen as a nonanatomic opacity in the maxillary antrum, or the displaced floor segment can be seen to disappear altogether if it is oriented in a way that inadequately attenuates the x-ray beam. An orbital floor blow-out fracture with frank enophthalmos appears as a bulbous soft-tissue mass extending from the expected level of the orbital floor into the maxillary antrum beneath. Indirect findings include asymmetric hemorrhage-related opacification of a paranasal sinus adjacent to a particular orbital surface. For example, an air-fluid level in the maxillary antrum suggests an orbital-floor injury. Unilateral opacification of the ethmoid air cells would suggest a possible medial-wall fracture. Another indirect plain radiographic finding is orbital emphysema. This pathologic collection of air is seen as a lucency at the superoposterior aspect of the orbit. Though passage of air into the orbit can theoretically occur via communication with any injured adjacent paranasal sinus cavity, orbital emphysema, when detected on plain images, is frequently from a blow-out fracture of the medial wall. Fractures of the medial wall and orbital roof are poorly visualized on plain radiographs. They are best defined on thin-section orbital CT studies. Degree of Confidence: When clinical suspicion of orbital fracture persists but the plain radiographic findings are equivocal or unremarkable, CT study is required for a more definitive assessment of the orbits. False Positives/Negatives: Infrequently, a maxillary sinus septum occurs near the orbital floor level, mimicking a trapdoor sign, but it is broader and oriented in the opposite direction. Unilateral opacification of paranasal sinuses adjacent to the orbits can occur with unrelated acute or chronic infection (eg, sinusitis) or with any obstruction of sinus drainage (eg, nasogastric tube). A large polyp or retention cyst at the superior aspect of the maxillary sinus could mimic appearance of a sunken globe. |
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Findings: CT study (see Image 3) of the orbits should, at minimum, be performed with 3 mm (or thinner) contiguous axial and direct coronal sections through the orbits, followed by coronal reconstructed imaging. However, if the axial CT sections are 2-3 mm or thinner, reconstructed images can be obtained in the coronal plane (via computer algorithms). CT allows the direct visualization of disrupted bony contours, fracture fragments, and associated sequelae to adjacent soft-tissue structures. Whether a fractured segment is displaced into or directed away from the orbit characterizes the fracture as a blow-in or blow-out injury. With blow-out fractures of the orbital floor, CT can directly depict the degree of enophthalmos, if any. Direct visualization of extraocular muscles aids in determining if the inferior rectus muscle is hooked or entrapped in an orbital floor fracture, if a similar injury to the medial rectus muscle against a medial wall fracture is present (uncommon), or if an injury has occurred to the superior rectus muscle with fracture of the orbital roof (rare). CT also permits the visualization of globe injuries, such as lens dislocation. Retrobulbar hematoma and subperiosteal hematomas may be observed as well. With orbital roof fractures, coronal CT images can display possible associated herniation of intraorbital contents into the frontal sinus or anterior cranial fossa. The development of multidetector-row/multisection (MDMS) spiral CT has dramatically increased imaging speed and anatomic coverage. In addition, the ability to achieve true volumetric imaging in combination with advances in virtual reality applications has improved surgical simulation. This progress translates into improved pretreatment planning, whether endovascular or surgical. New generations of software, such as that of the Vitrea 2D/3D system (Vital Images, Plymouth, MN), allow for rendering of soft tissues superficial to the underlying skeletal structures or selective removal of skin, muscle, and fat layers to improve visualization of the targeted bones. Dimensional reconstruction of the facial structures is especially useful in facial reconstruction planning. Contrast-enhanced multidetector-row CT angiography further allows for rapid vascular imaging to determine vascular compromise resulting from facial trauma. Degree of Confidence: CT is the study of choice for orbital fractures, offering the highest degree of confidence. Thin-section coronal images provide an excellent depiction of all orbital walls, especially the orbital floor and roof. Axial imaging is good for evaluating fractures of the medial and lateral walls. The positioning is more comfortable for the patient because axial imaging is easily performed with the patient supine. However, axial imaging alone is less than optimal for evaluation of the orbital roof and floor because fractures along those structures and any displaced fragments are commonly in the same section plane. Therefore, they are not ideally visualized. False Positives/Negatives: False-positive fracture diagnosis can result from misinterpretation of suture lines and foramina for fracture fissures. False-negative interpretation of images can result from an unusual fracture lines directed in the same imaging plane, which can result in fracture nonvisualization.
Findings: MRI has a negligible role in the initial assessment of acute orbital injury because of its poor depiction of subtle bony detail and because of the overriding requirement to exclude possible intraorbital metallic foreign bodies before exposing the patient to fluctuating magnetic fields. Metallic foreign bodies include bullet fragments or BB pellets left from an acute or previous penetrating trauma. In the setting of acute trauma, the patient's history is often incomplete, and bringing such a patient into the magnetic resonance field is strictly contraindicated. The patient might have been, eg, a sheet-metal worker or otherwise exposed to flying metal debris. After metal debris has been excluded from the orbits, preferably by means of CT imaging, MRI can be used for adjunct characterization of soft-tissue sequelae and complications of the above-described fractures. As with CT imaging, MRI can demonstrate globe injuries, retrobulbar fluid collections (hematoma or other), subperiosteal hemorrhage, and hemorrhage along the optic nerve sheath. Similar to CT, the proximity of extraocular muscles to the fracture edges is important to observe. Because of its multiplanar capability, MRI is particularly useful in evaluating complications of orbital roof fractures, as these injuries can impact the undersurface of the frontal lobes, result in encephaloceles, and be associated with herniation of intraorbital contents into the anterior cranial fossa.
Findings: Sonography is not generally applicable. Ultrasonography is used at major eye-trauma centers for evaluating intraocular structures. Degree of Confidence: Ultrasonography requires a dedicated ophthalmologic technician and may not allow visualization of important cranial injuries.
Findings: Nuclear medicine can play a pivotal role in the diagnosis and subsequent treatment where chronic or acute osteomyelitis is suspected. This can be particularly important when paranasal sinus infections involve the orbital walls. Infection in bone leads to early and tremendous changes in vascularity and a rapid osteoblastic response. Osteomyelitis can be diagnosed with great accuracy by using 3-phase technetium Tc 99m methylene diphosphate (MDP) bone study, as it identifies areas of increased bone-mineral turnover. 99mTc hexamethylpropyleneamine oxime (HMPAO) is generally more sensitive for the detection of acute osteomyelitis than chronic osteomyelitis. 99mTc HMPAO can also be used to differentiate septic from aseptic bone lesions. Although a negative bone scan can reveal old fractures and negate osteomyelitis, a positive bone scan may not help in differentiating acute, healing fractures from a bone infection. 99mTc-MDP–labeled WBCs or indium-labeled WBC single photon emission CT (SPECT) scans of the face and skull are positive in the presence of osteomyelitis, but they are also positive with acute fractures. A 3-phase bone scan is positive in the third phase and negative in blood flow and pooling in the presence of an old fracture. Osteomyelitis causes positive results in all 3 phases of a bone scan, but this finding does not discount the possibility of a new fracture. Hence, correlation with another finding on another imaging modality, eg, CT, can help confirm the diagnosis. Degree of Confidence: Three-phase phosphate scintigraphy has high sensitivity but low specificity because of the difficulty in differentiating between acute fracture deformities and osteomyelitis.
Findings: Selective catheterization of the external carotid arteries is necessary to identify vascular damage or a continued bleeding source caused by facial trauma. Angiography can be pivotal when orbital trauma, whether internal or external, is related to facial bleeding. Traumatic changes to the facial artery or other branches of the external carotid artery can result in expanding hematomas or intense nasal cavity bleeding. Such injuries can be amenable to endovascular repair. Head injuries in which the intracavernous carotid artery is torn, can result in traumatic carotid cavernous fistulas (CCFs). Such tears in the intracavernous carotid artery can result in redirected arterial flow into the ophthalmic veins causing variable degrees of exophthalmos. Selective angiography of the internal carotid artery (ICA) can clearly display the presence or absence of a CCF. See also Carotid-Cavernous Fistula.
Intervention: Intervention regarding the central retinal artery is inherently contraindicated, as it results in ischemia to the retina and visual compromise. Endovascular treatment of facial injuries requires special consideration. Unstable facial fractures can deter tight packing because of a lack of normal bony support structures. The small branches of the external carotid artery can be superselectively catheterized and embolized. Polyvinyl alcohol (PVA) and microcoils are the best choice for materials. Microcoils are often used to treat pseudoaneurysms of the branches of the external carotid artery, particularly the facial artery. To prevent recurrence from collateral retrograde blood flow, the parent vessel can be sacrificed both distal and proximal to the pseudoaneurysm. Traumatic CCFs can be closed with detachable balloons and/or coils, with the intent to maintain and improve patency of the parent ICA. Small CCFs may close without intervention (see Images 19-20 for before and after pictures). On the contrary, high-flow CCFs may occur secondary to large tears in the parent ICA. In select cases in which large tears are present, the patency of the parent ICA may be difficult to maintain, and ICA sacrifice may be warranted to close the fistula. Medical/Legal Pitfalls:
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