Emerg Radiol DOI 10.1007/s10140-014-1221-5

REVIEW ARTICLE

A systematic approach to CTevaluation of orbital trauma Aaron M. Betts & William T. O’Brien & Brett W. Davies & Omaya H. Youssef

Received: 15 January 2014 / Accepted: 1 April 2014 # Am Soc Emergency Radiol (outside the USA) 2014

Abstract Computed tomography (CT) is widely used in the initial evaluation of patients with craniofacial trauma. Due to anatomical proximity, craniofacial trauma often involves concomitant injury to the eye and orbit. These injuries may have devastating consequences to vision, ocular motility, and cosmesis. CT imaging provides a rapid and detailed evaluation of bony structures and soft tissues of the orbit, is sensitive in detection of orbital foreign bodies, and often guides clinical and surgical management decisions in orbital trauma. For this reason, radiologists should be prepared to rapidly recognize common orbital fracture patterns, accurately describe soft tissue injuries of the orbit, detect and localize retained foreign bodies within the globe and orbit, and recognize abnormalities A. M. Betts (*) Department of Radiology, University of Cincinnati Medical Center, 234 Goodman St., Cincinnati, OH 45267, USA e-mail: [email protected] A. M. Betts e-mail: [email protected] A. M. Betts Department of Radiology, San Antonio Military Medical Center, Fort Sam, Houston, TX, USA A. M. Betts : W. T. O’Brien Department of Radiology, Wilford Hall Ambulatory Surgical Center, Lackland Air Force Base, TX, USA W. T. O’Brien Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA B. W. Davies Department of Ophthalmology, University of Colorado Hospital, Aurora, CO, USA O. H. Youssef Audie L. Murphy Division, Ophthalmology Service, South Texas Veterans Health Care System, San Antonio, TX, USA

of the contents and integrity of the globe. In this review, we present a systematic approach to assist radiologists in the rapid evaluation of orbital trauma using the “BALPINE” mnemonic—bones, anterior chamber, lens, posterior globe structures, intraconal orbit, neurovascular structures, and extraocular muscles/extraconal orbit. Using this approach, we describe common traumatic findings within each of these spaces, and present common postsurgical appearances that can mimic findings of acute trauma. Keywords Orbital trauma . Orbital foreign body . Computed tomography

Introduction Due to anatomical proximity, craniofacial trauma often involves injury to the eye and orbit. Blunt trauma to the face can fracture osseous structures of the orbit and may damage soft tissue structures of the globe and orbit. These injuries can have devastating consequences to vision, ocular motility, and cosmesis. Penetrating injury also represents a significant threat to visual function from direct damage to structures of the eye and orbit upon initial injury or as a result of retained foreign bodies. Orbital and ocular trauma is common in industrialized countries. There are nearly 2.5 million new eye injuries annually in the USA, and approximately 1,400 of every 100,000 people in the USA will sustain an eye injury at some point in their lifetime [1, 2]. Eye injuries account for approximately 3 % of all visits to emergency departments [3]. Orbital and ocular injuries are also common in patients who suffer major trauma. Several studies have reported ocular injury rates between 9.8 and 16 % in the setting of major trauma, often with coexistent facial fracture [4–7].

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While clinical ophthalmologic examination is critical in the evaluation and management of patients with orbital trauma, computed tomography (CT) imaging provides a rapid and detailed evaluation of the osseous and soft tissues structures of the orbit. CT is also sensitive in the detection of retained foreign bodies that are not visible on ophthalmologic examination [8]. In more severe trauma, ophthalmologic examination may be limited due to decreased mental status, sedation, or comorbid injuries. Because CT imaging is widely used in the initial evaluation of patients with head and facial trauma, radiologists will often interpret trauma CT examinations before detailed ophthalmologic evaluation has been performed. Furthermore, CT imaging may reveal orbital injuries that were not initially suspected based upon the initial survey [9]. CT imaging may help guide the decision to pursue immediate surgery, delayed surgery, or nonoperative management. The orbit is a relatively small and anatomically complex space that contains many critical structures. This can make CT evaluation of orbital-facial injuries challenging. In this article, we present a systematic approach to CT evaluation of orbital trauma based upon the mneumonic “BALPINE” (bones, anterior chamber, lens, posterior structures of the globe, intraconal orbit, neurovascular structures, and extra-ocular muscles/extraconal orbit). This approach will help radiologists rapidly detect and describe critical injuries to the orbit and guide clinical management decisions with a goal of preserving vision, ocular motility, and cosmesis. Nontraumatic findings that may mimic sequelae of orbital and ocular trauma are also discussed. Bones The bony orbit is a pyramidal-shaped space with a roof, medial wall, floor, and lateral wall. The orbital surface of the frontal bone defines the majority of the roof, and the lesser wing of the sphenoid bone makes up a small portion of the roof at the orbital apex. The lateral wall is composed of the zygomatic bone anteriorly and the greater wing of the sphenoid bone posteriorly. The zygomatic bone also contributes to the orbital floor, while the maxillary bone makes up the largest portion of the orbital floor. The palatine bone also contributes a very small portion of the floor at the orbital apex. The medial wall from anterior to posterior consists of contributions from the maxillary bone, the lacrimal bone, the ethmoid bone, and the body of the sphenoid. It is also important to note the anatomical spaces that border the orbit. The anterior cranial fossa lies above the orbit. The floor of the orbit serves as the roof of the maxillary sinus. The medial wall separates the orbit from the ethmoid air cells. Orbital fractures may involve isolated fractures of a single wall or multiple walls. Additionally, there are complex facial fracture patterns have orbital involvement, including the zygomaticomaxillary complex (ZMC) fracture,

nasoorbitoethmoid fracture (NOE), and LeFort fracture patterns. These fracture patterns may be coexistent in severe facial trauma. Complex fractures with significant displacement may involve the orbital apex, with potentially devastating consequences to vision. Orbital floor fractures The most common fracture of the orbit is fracture of the orbital floor [10, 11]. The mechanism of injury typically involves direct anteroposterior blunt trauma to the globe and orbital margins. This results in energy transfer from the globe and/or orbital margin and subsequent fracture of the orbital floor. This is commonly known as a “blow-out” fracture because the fracture fragments are displaced inferiorly into the maxillary sinus. Proposed mechanisms for this fracture include hydraulic energy transfer through the globe and orbital soft tissues, and buckling of the floor from impact to the inferior orbital margin [12]. Complications from orbital floor fracture include orbital fat herniation through the osseous defect and entrapment of the adjacent inferior rectus muscle. The degree of displacement of the fracture fragment and relative area of the fracture fragment are important discriminators in predicting the need for surgery. Displaced fractures that involve greater than 50 % of the orbital floor or an area greater than 1 cm2 usually require surgical repair (Fig. 1) [13, 14]. However, the “trap door” fracture is an important exception to the correlation between size and displacement of the osseous defect and the indication for surgery. In this injury pattern, the orbital floor fracture fragment displaces and recoils, resulting in minimal net displacement of the fracture fragment. Due to increased elasticity of bone in younger patients, this pattern is more common in children. Clinically, the globe appears uninjured. For this reason, this injury is also known as the “white-eyed blowout” fracture. These patients have severe ocular motility impairment, and surgery is usually performed within 1–2 days to relieve the severe entrapment [15–17]. In identifying and describing this injury, it is important to detect the subtle nondisplaced or minimally displaced fracture. Evaluation of the adjacent inferior rectus muscle is also critical, which will be described in a subsequent section. Medial wall fracture After the orbital floor, the medial wall is the next most commonly fractured orbital wall. Similar to orbital floor fractures, the mechanism of injury usually involves blunt anteroposterior trauma to the globe and orbital margins. The lamina papyracea of the ethmoid in the medial orbital wall is the thinnest portion of the orbital walls. However, the thin medial orbital wall is reinforced by the numerous septae of the ethmoid air cells, thereby increasing the structural integrity of

Emerg Radiol Fig. 1 Right orbital floor fracture in a 30-year-old man post-assault. a, b Coronal and sagittal CT images show a large floor fracture involving greater than 50 % of the area of the orbital floor. Right maxillary sinus hemorrhage and extraconal orbital emphysema are also evident. The right inferior rectus muscle adjacent to the fracture appears normal. Patient underwent surgical repair 1 week later

the medial orbital wall. As with orbital floor fractures, the hydraulic theory and buckling theory have also been proposed to explain the mechanics of medial wall blow-out fractures [18, 19]. Medial wall fractures most commonly occur in association with orbital floor fractures, but can be seen as an isolated fracture (Fig. 2). In the absence of medial rectus entrapment, isolated medial wall fractures are often asymptomatic, but may be associated with diplopia [16, 18]. Enophthalmos is uncommon in isolated medial wall fractures, but can be seen with medial wall blow-out if there is sufficient loss of the normal posterior bulge of the lamina papyracea and resultant increase in orbital volume [16]. Enophthalmos is twice as common in combined medial wall and floor fractures compared to isolated orbital floor blow-out fractures [18]. Trap door fractures of the medial wall with medial rectus entrapment and severe ocular motility disturbance have been reported. Similar to trapdoor fractures involving the orbital floor, medial wall trapdoor fractures are seen almost exclusively in children, and require early surgical repair [18, 20].

In evaluating combined fractures of the orbital floor and medial wall, it is critical to assess for involvement of the inferomedial orbital strut, a bony strut connecting the maxillary and ethmoid bones in the inferomedial orbit. The anterior aspect of the inferomedial orbital strut contributes to the bony integrity of the inferomedial orbit, and is a site of attachment for the suspensory ligaments of the globe. The surgical repair of a combined floor and medial wall fracture with involvement of the inferomedial orbital strut is technically challenging, and there is risk of globe dystopia and persistent ocular motility problems if not corrected (Fig. 3) [21–23].

Fig. 2 Right medial orbital wall fracture in a 29-year-old man postassault. a, b Axial and coronal CT images show a fracture of the lamina papyracea of the medial orbital wall with herniation of orbital fat into the ethmoid air cells. Extraconal orbital emphysema is present. The right

medial rectus muscle is thickened and partially herniated into the medial wall fracture defect, concerning medial rectus entrapment or intramuscular hemorrhage/edema

Orbital roof fracture Isolated fractures of the orbital roof are typically caused by blunt injury to the forehead or superior orbital rim, and are much more common in children. The frontal sinuses are the last of the paranasal sinuses to develop in children, which contributes to the increased likelihood of orbital roof fractures

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Fig. 3 Left orbital floor and medial wall fractures in a 20-year-old man post-assault. a Coronal CT image shows inferiorly displaced fracture of the left orbital floor and fracture of the medial orbital wall. There is abnormal thickening of the left inferior rectus muscle, suggesting

entrapment or intramuscular hemorrhage/edema. b More anteriorly, coronal CT shows disruption of the left inferomedial orbital strut (black arrow). The right inferomedial orbital strut remains intact (white arrow)

in children compared to adults (Figs. 4 and 5). In adults, orbital roof fractures are more likely to be associated with complex high-energy facial trauma and are associated with significant ocular and intracranial injury (Fig. 6). The fracture fragment(s) of the orbital roof may be superiorly displaced (“blow-out” or “blow-up” fracture), inferiorly displaced (“blow-in” fracture), or nondisplaced. Orbital roof fractures may also extend to the orbital rim with or without frontal sinus involvement. Involvement of the adjacent superior rectus and superior oblique muscles may lead to entrapment and impaired ocular motility. Due to the anatomical relationship between the orbital roof and anterior cranial fossa, fractures of the roof are highly associated with violation of the dura, cerebrospinal fluid leak, and pneumocephalus. Growing fracture of the orbital roof is a late complication of orbital roof fracture seen exclusively in children, usually less than 3 years of age. The underlying mechanism likely involves dural laceration. CSF pulsations and normal cranial growth lead to herniation of brain parenchyma into the fracture line, with subsequent gliosis of the herniated brain. On CT imaging, this presents as a fracture defect that increases in width several months to years after initial injury [24, 25].

Zygomaticomaxillary complex fracture

Fig. 4 Superior orbital rim fracture in a 2-year-old girl who fell from a chair onto a tile floor. a Axial CT image shows nondisplaced fracture of the left superior orbital rim (arrow). The fracture did not extend deeper into orbital roof. b The fracture extends superiorly along the left anterior frontal bone (arrow). Note the lack of frontal sinus development

Due to the anatomical structure of the zygomatic bone, fractures of the lateral wall of the orbit usually present in association with more complex patterns of maxillofacial injury. The zygomatic bone has four bony articulations. Superiorly, the frontal process of the zygoma articulates with the frontal bone. Medially, the zygoma articulates with the maxillary. Laterally, the zygoma forms of a portion of the zygomatic arch, articulating with the zygomatic process of the temporal bone. Posteriorly, the zygoma articulates with the greater wing of the sphenoid, together forming the internal lateral wall of the bony orbit. These articulations make up the ZMC. Blunt trauma to the lateral face and orbit may fracture the four legs of the ZMC (Fig. 7). On CT imaging, this will show fractures of the lateral orbital margin, inferior orbital margin with extension into the anterior wall of the maxillary sinus, zygomatic arch, and internal lateral orbital wall [16, 26, 27]. This fracture was classically described by the misnomer “tripod” fracture based upon the visibility of the first three fractures on plain radiographs. Although describing this entity as a “tetrapod” or “quadripod” fracture is technically correct and preferred, the

Emerg Radiol Fig. 5 Orbital roof fracture in a 2-year-old boy who fell from a changing table. a, b Coronal CT images through the orbits show fracture of the right orbital roof with extensive superior extraconal hemorrhage adjacent to the fracture

“tripod” misnomer persists in clinical practice. It is important to note that tripod fracture, tetrapod fracture, quadripod fracture, and ZMC fracture are synonymous terms. There may be multiple orbital or ocular sequelae of ZMC fracture. Severe lateral angulation of the internal lateral wall of the orbit increases orbital volume and leads to enophthalmos, requiring orbital exploration as part of the surgical repair. ZMC fractures are also frequently associated with orbital floor fractures, which may further increase orbital volume. While enophthalmos can be assessed and measured on clinical examination, CT is critical in characterizing angulation and comminution of the internal lateral orbital wall fracture, as well as determining if there is coexistent orbital floor fracture. Similar to isolated orbital floor fractures, ZMC fractures with associated floor fractures are at risk for entrapment of the inferior rectus muscle. Major ocular injuries are also seen in 10 % of ZMC fractures [28].

In 1901, French military surgeon and professor René Le Fort published a classification scheme for describing maxillary fractures [29]. This classification scheme describes three variants of partial or complete dissociation of the maxillary bone from the skull base. In order for a Le Fort fracture to be

present, there m ust be a fracture involving the pterygomaxillary junction. This can involve fracture through the pterygoid plates of the sphenoid bone or through the posterior maxillary sinus wall. The anterior component of the maxillary fracture is what distinguishes the three Le Fort variants. Le Fort II and III fractures involve orbital wall fractures, whereas a pure Le Fort I fracture does not involve the orbit. All three Le Fort fractures are presented for completeness and to emphasize that multiple variants of Le Fort fractures can coexist. It is also important to note that Le Fort fracture patterns may be unilateral or bilateral, and can coexist with other orbital and facial fracture patterns. Le Fort I fracture occurs when there is horizontal fracture involving the anterior and medial walls of the maxillary sinus and the nasal septum. This dissociates the hard palate from the skull base (Fig. 8). In a Le Fort II fracture, there is oblique fracture of the zygomaticomaxillary articulation, involving the anterior maxillary sinus wall, inferior orbital rim, and medial orbital margin (Fig. 9). In a pure bilateral Le Fort II, the dissociated portion of the midface is roughly triangular, and is often referred to as a “pyramidal fracture.” A Le Fort III fracture is present when there is fracture of the medial and lateral walls of the orbit, as well as fracture of the zygomatic arch (Fig. 9) [16, 26].

Fig. 6 Orbital roof fracture in a 36-year-old man after a water skiing accident. a Sagittal CT in bone algorithm shows a comminuted inferiorly displaced (“blow-in”) fracture of the right orbital roof. b Sagittal CT in

soft tissue algorithm shows multiple foci of parenchymal hemorrhage/ contusion. Patient also had a right frontoparietal depressed skull fracture with adjacent subarachnoid hemorrhage (not shown)

LeFort fractures

Emerg Radiol Fig. 7 Zygomaticomaxillary complex fracture of a 54-year-old male post-assault. a Axial CT shows a minimally displaced fracture of the left lateral orbital margin. b The inferior left orbital margin is also fractured. c There is fracture of the left zygomatic arch. Extension of the inferior orbital margin fracture into the maxillary sinus is also present. d The left lateral orbital wall is fractured with mild angulation. e Three-dimensional reconstruction shows fractures of the left lateral and inferior orbital margins and the left zygomatic arch (arrows). These fracture lines define a three-legged fracture fragment. The fourth leg of the ZMC fracture pattern (the internal lateral orbital wall) is not visualized

Because Le Fort II and III fractures involve the orbit, there is potential for additional soft tissue orbital injury. Previous studies have shown that Le Fort III fractures are associated with increased risk of open-globe and other severe ocular injuries [30, 31]. Nasoorbitoethmoid fracture NOE fracture is a severe craniofacial injury pattern that involves high-energy impact to the nasoethmoidal region of the midface. While the mechanism does not necessarily involve direct blunt trauma to the globe or orbit, this fracture pattern can have devastating consequences on vision and ocular motility. The blunt injury to the nasoethmoid region causes fracture of the ethmoid sinuses and medial orbital wall. The impact usually

causes a blow-in type fracture of the medial orbital walls, with subsequent orbital volume loss (Fig. 10). This may cause an increase in the distance between the medial canthi of the eyes (telecanthus). Telecanthus is seen in up to 70 % of patients with NOE fractures [32, 16, 33, 34]. The degree of comminution of an NOE injury pattern describes the severity of injury, and may guide clinical and surgical management. The Manson system was devised to describe the degree of comminution of NOE fractures. The Manson classification also correlates with the likelihood of medial canthal tendon involvement. The medial canthal tendon anchors the tarsal plates of the upper and lower eyelid to the anterior and posterior lacrimal crests. In a Manson type I NOE fracture, there is a large fracture fragment that does not involve the

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Fig. 8 Right hemi Le Fort I fracture and right orbital floor fracture in a 31-year-old male after a motor vehicle accident. a Axial CT image through the maxillary sinus shows fracture of the right medial and lateral pterygoid plates. There are also comminuted fractures of the lateral and anterior walls of the right maxillary sinus and associated maxillary sinus hemorrhage. The right aspect of the hard palate is anteriorly displaced. b Coronal CT image through the face and anterior orbit shows fracture Fig. 9 Left hemi Le Fort II and Le Fort III in a 51-year-old women after fall from height. a Coronal CT image shows fracture of the left medial orbital rim (arrow). b The left medial orbital fracture extends to the left medial orbital wall (black arrow). Fracture of the left inferior orbital rim is also present (white arrow). c The inferior left orbital rim fracture extends into the left orbital floor (black arrow). Posterior/lateral maxillary sinus wall fracture is also present (white arrow), indicating a left Le Fort II pattern. Additionally, there is diastasis of the zygomaticofrontal suture at the lateral orbital margin (arrowhead). d Axial CT image through the orbit shows minimally displaced fracture of the lateral orbital wall (arrow). e Coronal CT image through the zygomatic arches shows subtle nondisplaced fracture through the left zygomatic arch (arrow), indicating a coexisting left Le Fort III pattern. Fractures of the left medial and lateral pterygoid plates were present (not shown)

involving the lateral and medial walls of the right maxillary sinus. Fracture of the hard palate is also present, with upward displacement of the “floating” right hemi-palate. Although pure Le Fort I fracture pattern does not involve the orbit, this patient had a coexisting minimally displaced right orbital floor fracture with involvement of the infraorbital nerve canal

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Fig. 10 Nasoorbitoethmoid fracture and open cranial injury in a 43-yearold man after assault with a hammer. a Axial CT image shows bilateral comminuted nasal and ethmoid fractures with “blow-in” type fracture of the anterior medial orbital walls. Additionally, there is a left lateral orbital wall fracture. b Fracture involves the right lacrimal drainage canal (arrow). c There is also comminuted fracture of the left lacrimal drainage canal (arrow) and comminuted left maxillary sinus fracture with associated hemorrhage in the left maxillary and sphenoid sinuses. d Coronal CT image through the anterior orbits shows comminution of the right medial orbital margin, indicating at least Manson II classification on the right

(black arrow). The left medial orbital margin is intact, indicating Manson I on the right (white arrow). e Axial CT through the frontal sinuses shows extensive fracture involving the anterior and posterior walls of the frontal sinuses. Comminuted depressed right frontotemporal skull fracture is also partially seen on this image. There is pneumocephalus over the frontal cerebral convexities. Pneumocephalus within the middle cranial fossa is also seen in images a–c. Skin wounds were approximated with staples prior to hospital transfer. f Axial CT image of the brain shows extensive subdural hemorrhage (arrows) over the left cerebral convexity with leftto-right midline shift

medial canthal tendon attachment. In types II and III NOE fractures, there is a higher degree of comminution involving the region of medial canthal tendon involvement. The distinction between types II and III is based upon the integrity of the osseous attachment of the medial canthal tendon attachment. The tendon remains attached in a type II, and is avulsed in a type III. Because the medial canthal tendon is not well evaluated by CT, the distinction between types II and III is a clinical or surgical diagnosis [16, 33]. The degree of comminution also correlates with increased likelihood of nasolacrimal duct involvement. Up to 20 % of patients with NOE fractures will have nasolacrimal duct involvement, and may result in abnormalities of tear drainage if not addressed surgically. Additional orbital fractures, including orbital floor and Le Fort II and III fractures are common with NOE. Severe ocular injuries may occur in up to 30 % of cases. Because NOE fractures involve significant high-energy blunt trauma, this

fracture pattern is often seen with intracranial injuries [32, 35]. Orbital apex When evaluating the bony structures of the orbit, the posterior third of the orbit, known as the orbital apex, is one of the most critical regions. The walls of the bony orbit converge posteriorly toward the orbital apex at the junction of the orbit and middle cranial fossa. Due to this anatomical configuration, the neurovascular structures of the orbit are particularly susceptible to injury when orbital fractures involve the orbital apex (Fig. 11). Because it carries the sensory fibers for vision, the optic nerve is among the most important structures to course through the constrained space at the apex of the orbit. Fractures involving the orbital apex usually occur as a complication of other orbital or facial fracture patterns, or as a result of traumatic fractures involving the skull base. Due to the high likelihood of neurovascular injury associated with orbital apex

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Fig. 11 Orbital apex fracture in 27-year-old man after assault with a baseball bat. a Axial CT image shows a comminuted fracture at the right orbital apex and the superomedial orbital wall. There is intraconal hemorrhage at the orbital apex, as well as a small amount of extraconal hemorrhage. b Coronal CT image through the orbital apices shows comminuted fracture of the right orbital apex involving the orbital roof

and medial wall, with hemorrhage into the right sphenoid sinus. Patient also had frontal sinus fracture with involvement of the anterior and posterior walls. A small amount of pneumocephalus can be seen lateral to the orbital roof fracture fragment. On clinical examination, patient had no light perception in the right eye

fractures, emergent surgical reduction and fixation may be indicated [16, 36]. Fracture involving the apex should be communicated immediately upon discovery to allow for early surgical intervention.

morphology of the globe is normal [43, 44]. Gas within the orbital soft tissues (orbital emphysema) may suggest penetrating orbital trauma. However, orbital emphysema is more likely to be as a result of orbital wall fracture that permits air entry from the maxillary, ethmoid, or frontal sinus. Wooden foreign bodies will appear similar to air density. Air density in linear and geometrical shapes should raise the concern for wooden foreign body, especially in the absence of orbital fracture. Distinguishing air from wood is particularly important due to the risk of infection from retained organic matter [45, 8, 46, 38, 47, 48]. It is also important to note that penetrating injury to the orbit may not be limited the globe or orbit. Orbital projectiles or impaled objects may continue their trajectory into the paranasal sinuses or cranial vault [49]. Although the globe is an anatomically small structure relative to body mass, the eye has a very sophisticated and complex anatomic and histologic structure. However, most of this complexity is beyond the resolution of CT imaging, and definitive evaluation of the globe is based upon clinical ophthalmologic examination. Nevertheless, it is important to evaluate the globe shape and the resolvable internal structures of the eye to help determine the need and urgency of further ophthalmologic evaluation. Before analyzing the key structures of the globe, it is important to note the position of the globe within the orbit. Enophthalmos may result from blow-out fractures of the orbit, a result of the increase in orbital volume. Enophthalmos may be evident at the time of injury in severely displaced blow-out fractures or with significant herniation of orbital soft tissues. However, traumatic orbital edema or hemorrhage may prevent enophthalmos in the acute post-traumatic period. Similarly, blow-in fractures will result in loss of orbital volume with subsequent proptosis of the globe.

Soft tissues One of the most important utilities of CT imaging in orbital trauma is the detection and localization of foreign bodies. While corneal and anterior chamber foreign bodies can be easily detected clinically by gross examination or biomicroscopy, CT is very sensitive in detecting foreign bodies both in the superficial structures and the deeper structures of the globe and soft tissue spaces of the orbit. Evaluation for foreign bodies within the globe is critical, as this is highly suggestive of open-globe injury and retained foreign bodies within the globe increase the risk of infectious or inflammatory endophthalmitis [37]. Metallic foreign bodies within the globe or orbital soft tissues may lead to long-term ocular toxicity if not removed. Furthermore, the presence of retained metallic foreign bodies within the globe or orbit is a contraindication to magnetic resonance imaging [8, 38]. CT is also sensitive in the detection of small stones [39, 40]. CT is somewhat less sensitive in the detection of glass foreign bodies. A 2001 study of glass detection by CT showed that 1.5 mm glass foreign bodies are detected 96 % of the time, and the sensitivity decreased to 48 % with 0.5 mm glass foreign bodies. Furthermore, the sensitivity varies based upon color and composition of the glass. Nevertheless, CT is more sensitive than either ultrasound or magnetic resonance imaging (MRI) in detecting glass foreign bodies [8, 41, 38]. Detection of plastic foreign bodies by CT is variable [42, 38]. Gas within the globe is highly suggestive of open-globe injury, even if the

Emerg Radiol Fig. 12 Anterior left open-globe injury in a 39-year-old man after being hit in the left eye with a nail. a Axial CT image of the right globe shows normal depth of the right anterior chamber. b Axial CT image of the left globe shows a shallow anterior chamber depth (white arrow) and posterior contour irregularity of the left globe (black arrows)

Globe shape must also be assessed for any abnormalities or asymmetry. The normal globe shape is nearly spherical, with a slight rounded prominence anteriorly due to the smaller radius of curvature of the cornea. The junction of these two curvatures is at the corneoscleral junction (limbus). Deformities of globe shape such as flattening of the posterior sclera (“flat tire” sign), irregular scleral contours, or alterations in anterior chamber depth suggest an open-globe injury [8, 44, 38, 50]. The sensitivity of CT in the detection of open-globe injury ranges from 56 to 75 %, while specificity ranges from 79 to 100 %. Ultimately, open globe from either blunt or penetrating trauma remains a clinical diagnosis. However, reporting the CT findings that suggest an open globe is important, as the severity of CT findings correlate to visual prognosis [43, 51, 44]. Furthermore, if there is concern for open globe, the eye should be protected with a non-occlusive rigid shield prior to definitive management. This will avoid inadvertent manipulation or pressure to the eye, which could expel globe contents.

Fig. 13 Posterior open-globe injury in a 35-year-old man after blunt trauma to the right orbit. Contrast-enhanced Axial CT image of through the globes shows a deep right anterior chamber compared to the left eye (arrow). There is sclera thickening and hyperenhancement of the right eye, and slight deformity of the posterior contour of the right globe. At the time of surgery, there was a complex scleral laceration posterior to the limbus, extending posterior to the equator in the superotemporal quadrant

Anterior chamber The anterior chamber is defined as the aqueous-filled space bounded anteriorly by the cornea and posteriorly by the anterior margin of the iris. Due to the superficial location and the optical clarity of the cornea, the cornea and anterior chamber are the most accessible areas of the eye for direct visualization by gross examination or slit lamp biomicroscopy. Some abnormalities of the cornea and anterior chamber may also be evident on CT imaging. Alteration or asymmetry in the anterior chamber depth may suggest open-globe injury. Open-globe injuries from corneal or anterior scleral lacerations may cause loss of the aqueous in the anterior chamber, resulting in collapsed anterior chamber depth (Fig. 12). Posterior open-globe injuries may cause decompression of the globe with posterior displacement of its contents, resulting in increased anterior chamber depth (Fig. 13) [52]. A 2009 study reported that differences in anterior chamber depth of 0.4 mm or greater (measured from the posterior margin of the cornea to the anterior margin of the

Fig. 14 Hyphema of the right eye in an 89-year-old woman after assault. Axial CT image through the orbits shows dense attenuation in the right anterior chamber (approximately 70 HU). V-shaped vitreous hemorrhage is also seen in the right eye. Patient has previously undergone bilateral cataract surgery with intraocular lens placement

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Fig. 17 Right lens displacement in a 55-year-old male. Axial CT image through the orbits shows absence of the lens in the right posterior chamber. There is a lentiform opacity adjacent to the sclera posterior to the nasal aspect of the limbus representing a partially extruded lens (arrow). At the time of surgical exploration, the lens was found between the sclera and conjunctiva

Fig. 15 Anterior chamber foreign body in a 19-year-old man with nailgun injury to the left eye. At the time of surgery, the metallic anterior chamber foreign body was abutting the anterior lens, without violation of the lens capsule

lens) showed a sensitivity of 73 % and specificity of 100 % for open-globe injury [53]. In addition to assessing the size and symmetry of the anterior chambers, it is important to evaluate for abnormal density within the anterior chamber. The normal aqueous should have simple fluid attenuation close to 0 HU.

Macroscopic blood in the anterior chamber (hyphema) will manifest as increased density of the anterior chamber fluid (Fig. 14) [46]. Corneal surface or anterior chamber foreign bodies may be visible on CT, depending upon the composition of the foreign body (Fig. 15). In supine patients, air within the anterior chamber will be seen in the antidependent margin along the posterior aspect of the cornea.

Lens The crystalline lens is an avascular proteinaceous structure that sits posterior to the iris and anterior to the vitreous. The

Fig. 16 Traumatic subluxation of the left lens in a 52-year-old woman after a motor vehicle collision. She suffered blunt trauma to the left eye from airbag deployment. Axial CT image shows oblique positioning of left lens. On clinical examination, the globe was intact

Fig. 18 Anterior dislocation of left intraocular lens (IOL) implant mimicking anterior chamber foreign body in a 69-year-old man who had previously undergone cataract removal in the left eye. Axial CT image through the orbits shows absence of a normal lens in the posterior chamber of the left eye. There is a thin linear opacity in the anterior aspect of the left eye (arrow), suggesting anterior chamber or posterior corneal foreign body. On clinical examination, the patient was found to have a degenerative corneal thinning (Terrien’s marginal degeneration) that had progressed to complete perforation at the nasal aspect of the limbus. The thin linear opacity corresponds to the IOL, which had prolapsed anteriorly due to decompression of the anterior chamber

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Fig. 19 Open-globe injury with traumatic expulsion of the lens and vitreous hemorrhage in a 54-year-old man after penetrating trauma to the right eye. a Axial CT image through the orbits shows layering hemorrhage in the right vitreous. No lens seen is seen in the right eye.

The patient had no prior history of eye surgery, suggesting traumatic expulsion of the right lens at the time of injury. b Sagittal CT image of the right orbit shows contour deformity of the right globe and layering vitreal hemorrhage

lens is suspended by thin zonular fibers attached at the periphery of the lens and the ciliary body. The lens provides about 1/3 of the total optical power of the eye and is responsible for accommodation, the process that allows the eye to adjust focus for distance and near. The lens sits within the aqueous-filled space of the posterior chamber bounded anteriorly by the posterior margin of the iris, posteriorly by the hyaline membrane of the anterior vitreous, and circumferentially by the ciliary body. The posterior chamber is anatomically different than the “posterior segment,” a term commonly used to refer to the collective structures of the posterior two thirds of the globe, and includes the vitreous, retina, and optic nerve head. Evaluation of the lens should include assessment of both the appearance and position of the lens, as well as the surrounding aqueous. On CT imaging, the normal lens is more attenuating than the surrounding aqueous within the posterior chamber, and is therefore easily visualized. The aqueous in the posterior chamber freely communicates with the aqueous in the anterior chamber through the pupil. As such, the posterior chamber aqueous should also have simple fluid attenuation close to 0 HU. In blunt trauma, the zonular fibers of the lens

may be disrupted, with resultant dislocation of the lens from its normal anatomic position. This can range from subluxation within the posterior chamber (Fig. 16) to dislocation into other anatomical spaces within the globe, usually within the vitreous. In an open-globe injury with zonular fiber disruption, the lens may be partially or completely expelled from the eye (Fig. 17). Traumatic cataract may result from compromise of the capsule of the lens in blunt or penetrating trauma. Capsular disruption of the lens can permit fluid accumulation and subsequent decrease in attenuation of the lens on CT [54, 55]. In severe cases of fluid accumulation, the lens may become isodense to the surrounding aqueous and not discernable as a separate structure by CT [56]. Intraocular foreign bodies may traverse through or land in the posterior chamber. Foreign bodies may also become lodged within the crystalline lens. It is important for the interpreting radiologist to be aware of postsurgical appearances of the lens that may mimic trauma. The most common postsurgical appearance of the lens is pseudophakia or removal of the native crystalline lens with placement of a silicone or acrylic intraocular lens (IOL). This procedure is most commonly performed for the treatment of

Fig. 20 Terson syndrome in a 17year-old female on ECMO. a Axial CT image through the orbits shows large left vitreous hemorrhage. Subtle layering density in the posterior right globe (arrow) also corresponds to vitreous hemorrhage. b Axial CT image through the brain shows extensive cerebral edema and subarachnoid hemorrhage. There is also profound diffuse edema of the scalp

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Fig. 21 Retinal and choroidal detachments in a 19-year-old man 1 week after severe blast and thermal injury. Axial CT image of the right orbit shows choroidal detachment of the right eye (arrows). Adjacent to the medial choroidal detachment, there is a second thin linear opacity that extends more posteriorly to the optic nerve head (curved arrow), suggesting detachment of the nasal aspect of the retina. Dense hemorrhage is also seen in the anterior vitreous, which severely limited clinical fundoscopic evaluation. The patient had undergone open-globe repair shortly after initial injury. Hypotony persisted despite globe repair. Due to poor prognosis for visual recovery, patient underwent enucleation approximately 1 week later

cataract (opacification of the lens). The implanted IOL preserves the optical power that was provided by the native crystalline lens. IOLs consist of a small optical component and flexible haptics that hold the IOL in place. IOLs are visible on CT, although the IOL is considerably thinner than the native crystalline lens [57]. IOLs have also been used both within the anterior chamber and posterior chamber without prior lens extraction (also called phakic IOLs) for the treatment of severe refractive error in patients who are not candidates for corneal refractive surgery procedures [58]. An IOL may mimic the appearance of an intraocular foreign body

Fig. 22 Hemorrhagic choroidal detachment in a 74-year-old man 1 week after being punched in the left eye. On clinical examination, patient had a large corneal laceration and hypotony, and large choroidal detachments were seen in all four quadrants on fundoscopic evaluation. Axial CT image through the orbits shows choroidal detachement in the left eye with heterogenous dense attenuation (arrows) indicating hemorrhagic choroidal detachments. The thin obliquely oriented linear density in the anterior globe (arrowhead) represents an IOL from prior cataract surgery, which was partially displaced from trauma

Fig. 23 Scleral buckle in a 59-year-old man. Axial CT image through the orbits shows dense silicone rubber encircling band around the left globe from a prior sclera buckle for treatment of a retinal detachment

(Fig. 18). Likewise, intraocular foreign bodies may be mistaken for IOLs [59]. Aphakia is the absence of a crystalline lens. In the context of trauma to the eye, aphakia raises the concern for traumatic expulsion of the lens (Fig. 19). However, aphakia from other causes such as prior cataract surgery without IOL placement, subsequent IOL removal due to complications, or congenital absence should also be considered. Posterior globe structures There are several structures of the posterior globe that should be evaluated, to include the vitreous, retina, choroid, and

Fig. 24 Scleral buckle in an 81-year-old man. Axial CT image through the orbits shows a metallic band encircling the left globe from a prior scleral buckle procedure for treatment of a retinal detachment

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Fig. 25 Vitreal silicone oil in an 86-year-old woman for treatment of macular hole. CT head was obtained after patient was brought to the emergency department after a fall. Axial CT image through the orbits shows hyperdense silicone within the vitreous, with a small crescent of simple fluid density along the posterior aspect of the vitreal space. The hyperdense appearance of the silicone oil may be mistaken for diffuse vitreal hemorrhage

sclera. However, in a normal eye, these structures are not individually resolved. The normal vitreous is a gel with a high water content and simple fluid attenuation on CT. As such, the aqueous in the anterior and posterior chambers will appear isodense to the vitreous. In a normal eye, the retina, choroid, and sclera remain closely apposed into a single resolvable layer on CT. The retina is a complex, organized ten-layer network of specialized neurons and supporting cells. The inner nine layers are known as the neurosensory retina, which

Fig. 26 A 59-year-old woman with history of psychosis and multiple episodes of self-inflicted injuries to the eyes; status, postbilateral vitrectomies with silicone oil placement. This study was obtained after acute self-inflicted wounds to the head and left eye. Axial CT image through the orbits shows homogenous hyperdense material in the right vitreous with small crescent of simple fluid attenuation in the right posterior vitreous. The left vitreous is also hyperdense, although more heterogenous. The left globe contour is irregular anteriorly and flattened posteriorly. On clinical examination, the left globe was open with full thickness corneal laceration. The bilateral hyperdense vitreous may be mistaken for diffuse bilateral vitreous hemorrhage

includes the photoreceptor cells (rods and cones) that convert light photons into neurochemical signals. The outermost layer is the retinal pigment epithelium (RPE), which provides metabolic support to the photoreceptor cells. The choroid is the middle vascular layer of the posterior portions of the eye. The choroid contains a network of permeable fenestrated capillaries and their feeding arterioles. The sclera is the tough outer connective tissue coat of the eye [60]. Similar to the anterior and posterior chambers, the vitreous should be scrutinized for foreign bodies, air, or increased attenuation suggesting hemorrhage. As discussed above, retained intraocular foreign body is associated with increased risk of endophthalmitis, and this risk is increased when the foreign body is located within the posterior segment [37]. Increased attenuation of the vitreous on CT imaging in the context of trauma is concerning for vitreous hemorrhage. This can manifest as increased attenuation within the substance of the vitreous (Fig. 14). Hemorrhage may also layer within the vitreous (Fig. 19). Hemorrhage may also occur in the subhyaloid space between the vitreous and inner layer of the retina, also called preretinal hemorrhage, which will show a thin curvilinear density along the interface between the vitreous and retina. Blood products in the subhyaloid space may ultimately dissipate anteriorly into the vitreous. While vitreous hemorrhage can be seen with a traumatic closed-globe injury, vitreous hemorrhage on CT is associated with increased risk of open-globe injury. Furthermore, the presence of vitreous hemorrhage in open-globe injury is associated with poor visual prognosis [43, 44]. When vitreal or preretinal hemorrhage is encountered, it is critical to note that this is not always a result of direct trauma to the eye or orbit. Bilateral hemorrhage in infants is highly suggestive of child abuse (“shaken baby syndrome”), which occurs as a result of acceleration/deceleration injury rather than direct orbital injury. Terson syndrome is a phenomenon in which preretinal/vitreal hemorrhages occur as a result of nontraumatic or traumatic intracranial hemorrhage. Vitreal hemorrhage associated with Terson syndrome is usually bilateral, but may be unilateral. The underlying mechanism is uncertain, but is believed to be a result of a sudden increase in intracranial pressure as a result of the intracranial hemorrhage. Terson syndrome is most commonly associated with subarachnoid hemorrhage, but can be seen with epidural, subdural, or intraparenchymal hemorrhage. Vitreous hemorrhages may be evident on initial noncontrast CT imaging of the brain (Fig. 20). Terson syndrome is usually associated with more severe neurologic injury and increased mortality [61–63, 60]. Vitreous hemorrhage can also occur in the absence of trauma in patients with proliferative diabetic retinopathy. Retinal detachment occurs when the neurosensory retina detaches from the RPE. Rhegmatogenous retinal detachment occurs secondary to retinal breaks, allowing vitreal fluid to percolate between the neurosensory retina and RPE. Trauma

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Fig. 27 Intraconal hemorrhage in a 25-year-old man after assault. a Axial CT image through the orbits shows extensive intraconal hemorrhage of the left orbit. b Coronal CT image shows medially displaced fracture of

the left medial orbital wall with extensive intraconal hemorrhage. The left medial rectus muscle is expanded and herniates into the fracture defect, suggesting left medial rectus entrapment

is the underlying mechanism in approximately 10 % of rhegmatogenous retinal detachments in adults, and is the most common cause of retinal detachment in children. Traumatic retinal detachment usually occurs weeks to months after openor closed-globe trauma, and it is extremely rare to see a new traumatic rhegmatogenous retinal detachment in the initial acute post-traumatic period [64]. Thus, a retinal detachment seen by CT imaging on initial trauma evaluation is much more likely to be chronic. A complete retinal detachment has a characteristic appearance on CT imaging. The neurosensory retina is tightly adherent posteriorly at the optic nerve head, and anteriorly at the ora serrata (junction of the retina and ciliary body epithelium). Thus, a complete retinal detachment will form a cone shape. On axial CT images, this will show a thin V-shaped line with the apex at the optic nerve head (Fig. 21) [46]. Choroidal detachment or effusion results from hypotony (extremely low intraocular pressure). The low pressure permits serous fluid entry into the highly vascular choroid and suprachoroidal space. This is most commonly seen in postoperative patients who have undergone a surgical procedure involving entry into the globe, such as cataract surgery, glaucoma surgery, or vitrectomy. However, hypotony can result from open- or closed-globe trauma (Fig. 21). Both traumatic and postsurgical choroidal detachments may be complicated

by hemorrhage into the serous effusion (Fig. 22). Chorodial detachment occurs anterior to the equator and elevates the retina, usually with minimal to no extension posterior to the equator. On CT imaging, this appears as crescentic or biconvex fluid collections extending from the ora serrata anteriorly, with little or no extension past the equator. Post-traumatic hemorrhagic choroidal detachments are more diffuse, and tend to be less elevated than postsurgical detachments. Serous choroidal effusions are usually managed with topical anticholinergics. However, massive “kissing” choroidal effusions will usually be drained by posterior retinotomy to avoid retinal adhesion [46, 60]. It is important to note that while a complete retinal detachment has a distinct V-shaped appearance, a focal choroidal detachment could appear similar to a partial retinal detachment. If the appearance of a detachment on CT imaging does not present as one of these classic patterns of choroidal versus complete retinal detachment, both of these entities should remain in the differential diagnosis. Scleral buckling for the treatment of retinal detachments was first used in 1949. A scleral buckle relieves traction on a retinal break, closes the break, and prevents vitreous fluid entry between the RPE and neurosensory retina. The buckle is secured in place to the globe by sutures and an encircling band. The encircling band will cause an indentation of the globe and is usually associated with an increased axial length

Fig. 28 Left intraconal foreign body and open globe in a 20-year-old woman after being shot in the left eye with a BB gun. a Axial CT image through the orbits shows metallic foreign foreign body within the left intraconal orbit near the orbital apex. b Coronal CT image through the posterior orbit shows the BB inferolateral to the optic nerve. c There is

posterior intravitreal air and hemorrhage in the left eye. At the time of surgical exploration, both anterior and posterior scleral wounds were identified, consistent with entrance and exit wounds, respectively. The site of intravitreal air and hemorrhage corresponds to the exit wound

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Fig. 29 Carotid-cavernous fistula in a 33-year-old woman after being hit by a moving vehicle. The patient suffered multiple injuries to include facial and skull base fractures and intracranial hemorrhage. a Axial CT angiogram in arterial phase shows early filling of an enlarged left superior ophthalmic vein (white arrow). Pseudoaneurysm of the left cavernous

carotid also protrudes through a fracture in the sphenoid body into the sphenoid sinus (black arrow). b Lateral digital subtraction angiogram of the left internal carotid artery shows early filling of the left cavernous sinus and retrograde filling of the superior ophthalmic vein

of the globe. The buckle may be composed of silicone or rubber, with variable density of the buckle material and sutures (Fig. 23). Some of components may be metallic, and may be mistaken for metallic projectile foreign bodies in trauma (Fig. 24) [65, 46, 60]. The last several decades have seen tremendous advances in vitreoretinal surgical techniques. Vitrectomy with placement of intraocular air or gas, perfluorocarbon liquids, or silicone oil has been used as a means of intraocular retinal tamponade [64]. Air, gas, and perfluorocarbon liquids provide temporary tamponade, while silicone oil will persist within the vitreous until removal. These procedures can lead to various postoperative changes of the vitreous on CT imaging and can mimic post-traumatic changes. Temporary tamponade with air or gas (most commonly SF6 or C3F8) will appear similar to posttraumatic intravitreal air, mimicking an open-globe injury [66–68]. Silicone oil is denser than normal vitreous, with attenuation up to 130 HU, and may mimic complete vitreous hemorrhage (Figs. 25 and 26) [46, 68]. Perfluorocarbon liquid is rarely seen on imaging, as it is removed intraoperatively to avoid retinal toxicity. However, any retained perfluorocarbon will appear very dense relative to normal vitreous, and may be mistaken for an intravitreal foreign body [66].

dividing the orbit into an intraconal and extraconal space. The fascial network also serves to suspend the globe within the orbit fat. The intraconal space of the orbit should be scrutinized for hemorrhage, foreign bodies, and air. Hemorrhage will manifest as poorly defined increased density within the orbital fat (Fig. 27). If the volume of intraconal (retrobulbar) hemorrhage is sufficient to cause mass effect, this may lead to proptosis of the globe and tenting of the posterior globe from optic nerve traction. It is critical to immediately report any mass effect in the

Intraconal orbit The soft tissues space of the orbit posterior to the globe contains a large quantity of fat. The orbital fat allows excellent visualization of the extraocular muscles, optic nerve, and larger vascular structures of the orbit with noncontrast CT evaluation in trauma. The four extraocular rectus muscles (superior, inferior, medial, and lateral) have a common tendinous attachment at the annulus of Zinn in the orbital apex. The intervening fascia forms a conical space within the orbit,

Fig. 30 Large inferiorly displaced right orbital floor fracture in a 17-yearold girl after assault. The fracture involves greater than 50 % of the orbital floor with associated maxillary sinus hemorrhage. There is expansion of the right inferior rectus muscle, concerning for entrapment. On clinical evaluation, she had diplopia in upward gaze, and restriction of upward gaze in the right eye. She underwent surgical repair 1 week later

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Fig. 31 Lateral rectus hematoma in an 87-year-old woman after fall from height. She takes clopidogrel and aspirin daily. a Axial CT image through the orbits shows large heterogenous expansion of the left lateral rectus with significant proptosis of the left globe and tenting of the posterior globe contour, concerning for orbital compartment syndrome. b Coronal

CT demonstrates mass effect on the optic nerve with medial displacement of the nerve. There is an inferiorly displaced left orbital floor fracture with maxillary sinus hemorrhage. On clinical examination, she had no light perception in the left eye, and the intraocular pressure was markedly elevated to 90 mmHg, consistent with orbital compartment syndrome

orbit, as proptosis from orbital hemorrhage can cause orbital compartment syndrome (OCS) due to increased retrobulbar pressure, which leads to increased intraocular pressure and neurovascular compromise. However, orbital compartment syndrome is not synonymous with orbital hemorrhage. Orbital hemorrhage may occur without proptosis or neurovascular compromise. Furthermore, patients may develop OCS from significant orbital edema or volume loss due to blow-in type fractures [69, 70]. Foreign bodies in the intraconal orbit should be described in terms of size, density, position, and spatial relationship to the optic nerve (Fig. 28). Because the optic nerve courses through the intraconal space of the orbit, foreign bodies within this space may lead to direct injury to the optic nerve. Air within the orbital fat (orbital emphysema) may be seen with fractures that involve communication with paranasal sinuses, and can also be seen with penetrating trauma. As described previously, air density in geometric shapes raises suspicion for a wooden foreign body, especially in the absence of orbital fractures.

Neurovascular structures

Fig. 32 Trapdoor fracture in a 10-year-old boy who was struck in the eye with a baseball. a Coronal CT image through the orbits shows absence of the right inferior rectus muscle within the right orbit. There is soft tissue and fat density along the roof of the right maxillary sinus, consistent with herniation of the inferior rectus and orbital fat. b Coronal CT image at the

same level in bone window shows a nondisplaced fracture of the right orbital floor. On bone windows, the distinction between soft tissue and fat attenuation is less conspicuous, and the herniated contents could easily be mistaken for a mucosal polyp or retention cyst

The optic nerve (cranial nerve II) is a central nervous system tract that transmits visual sensory information from the retina to the lateral geniculate nucleus of the thalamus. The intraorbital portion attaches to the posterior globe, courses centrally through the intraconal orbit, and enters the cranial vault through the optic canal at the orbital apex. It is surrounded by a dural sheath and cerebrospinal fluid, and the central retinal artery and vein course centrally through the nerve throughout the majority of its intraorbital course. There is a complex network of sensory, motor, and autonomic innervation to the globe and orbit [60]. However, this intricate network of smaller nerves is beyond the resolution of meaningful evaluation with CT, and the optic nerve is the only nerve within the orbit that can be meaningfully and consistently evaluated by CT in trauma. The optic nerve should be examined throughout its intraorbital course. Foreign bodies within the orbit may impinge on the optic nerve. The location of a foreign body relative to the optic nerve should be reported, and any contact

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Fig. 33 Lateral extraconal hemorrhage in a 66-year-old man with minimally displaced left ZMC and orbital floor fractures after fall from standing. a Coronal CT image through the orbits in soft tissue window shows heterogeneous density in the lateral extraconal space with medial displacement of the left lateral rectus muscle belly (arrow). b Coronal CT

image through the same level in bone window shows the lateral extraconal hemorrhage adjacent to a left lateral orbital wall fracture. There is a minimally displaced left orbital floor fracture with associated maxillary sinus hemorrhage

or impingement of the optic nerve should also be noted. Because the orbit is a pyramidal-shaped space, there is little room to spare as the optic nerve approaches the orbital apex and optic canal, and there is an increased likelihood that foreign bodies at the orbital apex will impinge on the optic nerve. Displaced fractures involving the orbital apex can also impinge on the optic nerve. Identifying a displaced fracture at the orbital apex is critical, as this may prompt early surgical management. The optic nerve may also be lacerated, transected, or avulsed, with devastating consequences to vision [49, 16, 46]. The arterial supply to the globe and orbit is provided by the internal carotid circulation via the ophthalmic artery, and there is extensive anastomosis anteriorly in the orbit with superficial branches from the external carotid circulation. The major venous drainage of the orbit is served by the superior and inferior ophthalmic veins, which ultimately drain via the internal jugular vein. The superior ophthalmic vein is the only vascular structure of the orbit that is consistently visualized on CT imaging. The size of the superior ophthalmic vein is variable, typically between 1.5 and 3 mm in diameter [71]. Asymmetry in the caliber of the superior ophthalmic veins raises the concern for abnormality affecting venous drainage, such as carotid-cavernous fistula, which can be seen acutely in the post-traumatic period, or may have a delayed onset. CT angiography and conventional catheter angiography will show early filling of the superior ophthalmic vein during arterial phase (Fig. 29). It is important to note that various nontraumatic conditions can also cause superior ophthalmic vein enlargement, including normal variant, orbital varix, orbital Grave’s disease, cavernous sinus thrombosis, and orbital pseudotumor [46, 72].

(Figs. 2, 3, 27, and 30). Herniation of a muscle adjacent to a fracture into the osseous defect and rounding of the muscle belly in cross-section are highly suggestive of muscular entrapment. The rounding of the muscle belly is most likely a result of disruption of the fascial sling that normally maintains an oval or flattened morphology. Rounding of the muscle belly may also be seen with intramuscular hemorrhage. This finding is best evaluated in the coronal CT images, as this plane will display the rectus muscles in cross-section and simultaneously displays the rectus muscles of the contralateral orbit in order to compare for symmetry. CT findings suggesting entrapment should be promptly reported as muscle entrapment may prompt the need for surgical management [16, 73]. However, the interpreting radiologist should recognize that the diagnosis of muscular entrapment is ultimately based upon clinical examination. The extraocular muscles should still be closely evaluated even if a fracture is minimally displaced or if no fracture is detected. Rounding or expansion of a muscle belly may be seen in the absence of fracture or in association with fracture without entrapment. This is due to intramuscular hemorrhage or edema (Fig. 31) [74, 75]. The absence of an extraocular muscle in the orbit may be seen with trapdoor fractures of the orbital floor, in which the muscle herniates into the maxillary sinus (Fig. 32) [16]. Absence of an extraocular muscle may also rarely be seen with complete muscle rupture/avulsion [76–79]. Partial extraocular muscle tear has also been reported [80]. Similar to the intraconal orbit, the extraconal orbit should be evaluated for foreign bodies, hemorrhage, or air. Hemorrhage into the extraconal orbital fat will appear similar to hemorrhage within the intraconal fat (Figs. 5 and 33). Orbital hemorrhage will often be seen within both the intraconal and extraconal spaces. Rarely, extraconal hemorrhage may present as a focal subperiosteal hemorrhage after trauma. These usually present with significant mass effect and require surgical evacuation [81, 82].

Extraocular muscles and extraconal orbit One of the most common abnormalities of the extraocular muscles in trauma is entrapment within an orbital wall fracture

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Conclusion Orbital trauma may occur as an isolated injury or in the context of more severe craniofacial injury. Due to sensitivity and rapid acquisition time, the use of CT evaluation in trauma has become common practice. Therefore, radiologists are critical in the multidisciplinary approach to trauma management and are frequently called upon to provide rapid and accurate assessments to guide further management of trauma patients. Familiarity with orbital anatomy, common injury patterns, foreign body detection, and sight-threatening complications will maximize the accuracy and timeliness in CT evaluation of orbital trauma. In evaluating the structures of the orbit, the “BALPINE” mnemonic offers a simple and rapid approach to evaluate the osseous and soft tissue structures of the orbit and ensures that the critical structures of the orbit are not overlooked.

Conflict of interest The authors declare that they have no conflict of interest.

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