ANATOMY REVIEW

The facial region is comprised by 5 unpaired and 6 paired bones. These bones are distributed in:

• 3 facial thirds.

Fig 1: The images on the left represent the 3 facial thirds; the 9 images on the right are a step-by-step illustration of the bony structures encompassed in the mid facial third. The upper third only contains the frontal bone (orange). There are 9 different bones, either paired or unpaired, in the mid third: sphenoid bone (red), ethmoid bone (green), palatine bones (grey), vomer bone (dark brown), inferior turbinate bones (light brown), lacrimal bones (purple), maxillary bones (yellow), nasal bones (pink) and zygomatic bones (lilac). The mandibular bone (light blue) is equivalent to the lower facial third.

• 7 facial subunits.

Fig 2: The images on the right represent the 7 facial subunits. The upper facial third only contains the frontal bone and, thus, the frontal region (1). 5 facial subunits can be delimited in the mid third: the orbits (2), the naso-orbito-ethmoidal (NOE) complex (3), the nasoseptal (NS) region (4), the zygomaticomaxillary complex (ZMC) (5) and the maxillary occlusion-bearing (MOB) fragment (6). The mandibular region (7) is the only one located in the lower facial third.

• 8 facial buttresses.

Fig 3: This image shows the 8 facial buttresses or areas of greatest facial bone thickness; they are responsible for structural support, facial dimensions and force distribution and, therefore, the key points to be surgically reconstructed when fractured. There are 4 horizontal and 4 vertical buttresses; the first word makes reference to whether the buttress sits on either the maxillary or the mandibular bone, and the second word depends on the position of the buttress in said bone. The horizontal buttresses are the upper transverse maxillary (yellow outlining), the lower transverse maxillary (green outlining), the upper transverse mandibular (orange outlining) and the lower transverse mandibular (purple outlining) buttresses. The vertical buttresses are the medial maxillary (red outlining), the lateral maxillary (blue outlining), the posterior maxillary (brown outlining) and the posterior mandibular (magenta outlining) buttresses.

OPTIMAL IMAGING TECHNIQUE

The CT scan images should be acquired in a parallel plane to the hard palate and include every structure comprised between the frontal sinuses and the mandibular symphysis. Two sets of images should be acquired:

• Bony-window axial images, no more than 1 mm thick: these allow for optimal sagital and coronal multiplanar reconstructions.
• Soft tissue-window axial thicker images: they are appropriate for volume rendering reconstructions.

No intravenous contrast is required, unless vascular lesion is suspected.

FACIAL FRACTURES

Standard aspects to be reported:

• Uni- or bilateral involvement of bones.
• Presence of comminution.
• Presence of displacement.

FACIAL FRACTURES: UPPER THIRD

FRONTAL FRACTURES

The most commonly fractured structure in the frontal bone is the anterior wall of the frontal sinus, followed by both the anterior and posterior walls. Whenever the posterior wall is the only one fractured, the skull base and cranial vault should be examined, as they could harbour the source fracture.

Frontal fractures can spread:

• Inferiorly: the superior orbital rim will be involved.
• Medially: the frontonasal duct should be checked. This is the drainage tract of the frontal sinus into the nasal cavity, through the middle nasal meatus. When fractured, a mucocele could arise.
• Posteriorly: the anterior cranial fossa is immediately behind the frontal bone. Therefore, cerebrospinal fluid leak, encephalocele, pneumocephalus and traumatic or infectious intracranial complications may develop.

Fig 4: The most commonly fractured parts of the frontal bone are the anterior wall of the frontal sinus (bright red circle in the upper right image) and its posterior wall (muted red circle in the upper right image). The different spreading pathways of frontal fractures are depicted in the lower images: the superior orbital rim (magenta arrow), the frontonasal duct (yellow arrows) and the anterior cranial fossa (blue arrow). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), anterior cranial fossa (ACF).

Fig 5: Bilateral frontal fracture involving both the anterior and posterior wall of both frontal sinuses (3D and red arrows). The fracture spreads inferiorly to both superior orbital rims (magenta arrows), posteriorly towards the anterior cranial fossa, with a resulting pneumocephalus bubble (blue arrow), and medially (yellow arrow in the axial view). Nevertheless, both frontonasal ducts remain intact (yellow arrows in sagital views). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D).

FACIAL FRACTURES: MID THIRD

NASOSEPTAL (NS) REGION FRACTURES

The NS region is the most commonly involved in facial fractures. It is comprised by:

• Bony nasal pyramid or nasal bones: they articulate with the frontal bone (frontonasal suture) and the frontal process of the maxillary bone (nasomaxillary sutures).
• Nasal septum: its degree of deviation should be reported.
  • Posterior bony segment: it is formed by the perpendicular plate of the ethmoid bone and by the vomer.
  • Anterior septal cartilage: it is continuous with the anterior nasal spine in the maxillary bone, whose fracture entails greater risk for cartilaginous lesion and septal haematoma, necrosis and perforation.
• Nasal cartilages

Fig 6: The picture on the left highlights the nasoseptal region. The pictures on the right show the nasomaxillary sutures (yellow arrows), the nasofrontal suture (orange arrow), the anterior nasal spine (yellow circle) and the perpendicular plate of the ethmoid bone (green outlining) and the vomer bone (brown outlining) that form the bony aspect of the nasal septum. Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG).

Fig 7: The images on the left side of the white vertical bar, show a bilateral, simple and nondisplaced nasal fracture. The nasofrontal suture (orange arrows), nasal septum (green arrow) and anterior nasal spine (yellow circles) remain intact, while the fracture line crosses the left nasomaxillary suture (red arrows). On the other hand, the image on the right contains a bilateral, comminute and displaced nasoseptal fracture (red circle), in which the nasal septum is also involved (red arrow). Abbreviations: axial view (AX), sagital view (SAG), volume rendering reconstruction (3D).

NASO-ORBITO-ETHMOIDAL (NOE) COMPLEX FRACTURES

5 cardinal or key tracts define the NOE complex (see "figure 8"). The involvement of at least 4 of them is imperative to report a NOE complex fracture. The state of the following structures should be noticed and reported when encountered with such fractures:

• Medial canthal tendon insertion area: the state of the tendon can not be accurately demonstrated on CT scan, but the degree of comminution of the NOE complex fracture is an indirect sign of the condition of said tendon. The classification of Markowitz and Manson is used for this purpose. Its impairment could result in telecanthus. See "figure 8".
• Nasolacrimal duct: this is the drainage path of the lacrimal sac to the nasal cavity, through the inferior nasal meatus. Its fracture and impairment could lead to chronic epiphora, dacryocystitis or recurrent dacryocystoceles.
• Frontal sinus and, specifically, the frontonasal duct: explanation on "Frontal fractures" and "figure 4".
• Cribiform plate of the ethmoid bone: it is continuous with the anterior cranial fossa and it contains the olfactory nerve (cranial nerve I) and ethmoidal vessels. Therefore, the extension of fracture lines through the cribiform plate could result in intracranial complications (mentioned in "Frontal fractures"), rhinorrhea, epistaxis or anosmia.

Enophtalmos and exophtalmos (explanations on "Orbital fractures") should also be reported.

Fig 8: The picture on the left highlights the naso-orbito-ethmoidal (NOE) complex and the 5 cardinal tracts that define it: 1. Vertical tract along the nasal bone and the piriform aperture (blue line). 2. Medial maxillary buttress (yellow line). 3. Inferior orbital rim and orbital floor (green line and green translucent square). 4. Medial orbital rim and medial orbital wall (purple line and purple translucent square). 5. Frontomaxillary suture (red line). The pictures on the centre, between both dark blue vertical bars, represent the medial canthal tendon insertion area, which is composed of the medial orbital rim (yellow arrow), the lacrimal crest (oblique purple arrow) and the lacrimal fossa that contains the lacrimal sac (vertical purple arrow). The state of this insertion area should be reported with the Markowitz and Manson classification (green rectangle): the MOE complex fracture could contain a single fragment and said insertion area within it (type I), or be comminute, with no fracture line accross the insertion area (type II) or with it (type III). The pictures on the right side of the right dark blue vertical bar, illustrate the nasolacrimal duct (light blue arrows), the frontonasal duct (orange arrows) and the cribiform plate of the ethmoid bone (highlighted area on the 3D picture and green arrow). Abbreviations: coronal view (COR), sagital view (SAG).

Fig 9: Example of a comminute and displaced left NOE complex type III fracture, according to the Markowitz and Manson classification; the fracture seems to cross the insertion area of the medial canthal tendon (red circle). All of the cardinal lines of the NOE complex are involved (arrows and numbers matching the colours in figure 8) and the fracture spreads to the left lacrimal duct (light blue circle); the frontonasal duct and the cribiform plate of the ethmoid bone remain intact. Abbreviations: volume rendering reconstruction (3D), axial view (AX).

ORBITAL FRACTURES

The orbit is delimited by the orbital rim and walls and contains the eye globe, the extraocular muscles, fibrofatty tissue and neurovascular structures (see "figure 10").

Fig 10: The upper images illustrate the orbit, composed of the orbital rim (red outlining) and the orbital walls: orbital floor (yellow outlining) (maxillary, zygomatic and palatine bones), medial wall (green outlining) (maxillary, lacrimal and sphenoid bones and lamina papyracea of the ethmoid bone), orbital roof (orange outlining) (frontal bone and lesser wing of the sphenoid bone) and lateral wall (purple outlining) (zygomatic bone and greater wing of the sphenoid bone). Note that the orbital roof is adjacent to the anterior cranial fossa and that the lamina papyracea of the ehtmoid bone contains the ethmoidal arteries (red arrows), which, when injured, could cause intraorbital haematoma. The lower soft-tissue images show the extraocular muscles: medial rectus muscle (magenta outlining), lateral rectus muscle (green outlining), superior rectus muscle (blue outlining), inferior rectus muscle (yellow outlining), superior oblique muscle (orange outlining) and inferior oblique muscle (purple outlining). These 6 muscles form a cone-shaped space between them, the intraconal space; the intraorbital space outside this area is the extraconal space (yellow highlight). The yellow asterisk marks the optic nerve or cranial nerve II. The lower image on the right highlights in light blue the interior orbital buttress. Abbreviations: coronal view (COR), sagital view (SAG).

Orbital fractures' classification depends on the evaluation of the following structures and will determine the need for alignment or surgical intervention:

• Orbital rim -> Pure (orbital rim intact) vs impure (orbital rim involved).
• Internal orbital buttress -> Simple (internal orbital buttress preserved) vs complex (internal orbital buttress fractured). The internal orbital buttress is formed by the confluence of the medial wall of the maxillary sinus, the medial wall of the orbit, and the orbital floor.
• Orbital content -> Blow-out (orbital content displaced beyond the orbital walls) vs blow-in (content displaced into the orbit). 
  • When encountered with anomalous location of extraocular muscles outside the orbit (typically, the inferior rectus muscle in the maxillary sinus) witch correct alignment of the orbital walls, a trapdoor fracture should be reported; typically seen in children and self-reducing, but with high risk of muscle strangulation.

The most common fractures are blow-out fractures involving the orbital floor or, less frequently, the medial wall.

Acute inflammation and haemorrhage could either mask enophthalmos due to an orbital blow-out fracture or lead to an orbital compartment syndrome; both requiring surgical intervention. 

• The CT-based predictors of late noticeable enophthalmos are:
  • Involvement of > 2 cm² or > 25-50% of the orbital floor or medial wall.
  • Fracture of the internal orbital buttress.
  • Herniation of > 1.5 ml of fibrofatty tissue outside the orbit.
• Suspicion of orbital compartment syndrome should be arised in the following scenario (see "figure 11"):
  • Marked proptosis
  • Tenting of the posterior globe
  • Stretching of the optic nerve

Fig 11: This image represents the measurements that, besides the stretching of the optic nerve, are needed to rule out an orbital compartment syndrome in CT scan. Firstly, at the level of the optic nerve’s insertion in the posterior globe, a line between the most anterior part of both zygomatic bones ought to be traced, the interzygomatic line (purple horizontal line); this is the reference line for measurements of proptosis, which are the distance from this line to the most anterior and the most posterior surfaces of the globe (red vertical lines). Proptosis is defined by an interzygomatic line – anterior surface distance > 23 mm or an interzygomatic line – posterior surface distance < 5.9 mm. In order to report tenting of the posterior globe, the posterior globe angle (blue angle) should be < 130º; an angle < 120º would indicate severity. This angle is measured at the insertion point of the optic nerve in the posterior globe, by tracing two tangent lines and measuring the angle between them. Abbreviations: axial view (AX).

The following structures should also be assessed:

• Infraorbital canal: see "figure 12".
• Optic canal: see "figure 12".
• Superior orbital fissure: see "figure 12".
• Inferior orbital fissure: see "figure 12".
• Extraocular muscles: see "figure 10". Any asymmetry, angled trajectory or herniation should be reported as a sign of possible lesion.
• Fibrofatty tissue: its herniation to periorbital structures should be reported, most frequently to the paranasal sinuses.
• Intraorbital foreign bodies, haematoma or emphysema: see "figure 13".
• Globe: see "figure 13".

Fig 12: These images show the main canals and fissures at risk of injury in orbital fractures. The infraorbital canal (yellow path) originates in the orbital floor and contains the infraorbital nerve; therefore, it is responsible for feeling in the cheek and maxillary gums. There are three distinct orifices in the posterior aspect of the orbit: the optic canal (pink dots and outlining), the superior orbital fissure (green dots and outlining) and the inferior orbital fissure (blue dots and outlining). The optic canal (pink dots and outlining) is the passageway for the optic nerve or cranial nerve II and the ophtalmic artery; its lesion can lead to amaurosis and there is higher risk for it when the fracture is less than 1 cm away from this canal. The superior orbital fissure (green dots and outlining) is crossed by cranial nerves III, IV and VI, by the V1 branch of cranial nerve V and by the superior ophtalmic vein, leading to multiple signs and symptoms encompassed in the superior orbital fissure syndrome when injured. The posterior insertion of the extraocular muscles or annulus of Zinn involves structures of both these orifices and the sum of all the consequences of its lesion is referred to as the orbital apex syndrome. Finally, the inferior orbital fissure (blue dots and outlining) contains the V2 branch of cranial nerve V, the infraorbital artery and the inferior ophtalmic vein. Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG).

Fig 13: These images show posible findings in the context of trauma and/or orbital fracture, regarding the ocular globe. Spontaneously hyperdense content compatible with haematoma can develop in different locations: in the anterior chamber of the anterior segment (hyphema), in the posterior segment (hemovitreous) (red asterisk and arrow) ,V-shaped in the posterior segment (secondary to retinal detachment) (white asterisks and arrows) or acquiring a lentiform or biconvex shape in the posterior segment (secondary to choroidal detachment) (black asterisks and arrows). The lens could either appear hypodense (traumatic cataract) or in an abnormal position (luxation if completely detached from the ciliary bodies; purple arrow) (subluxation when the union to the ciliary body is preserved; green arrow). Changes in the globe surface’s morphology and loss of round shape and volume (“flat tyre” sign) are signs of globe rupture (orange arrows). Foreign bodies should be reported and their probable nature guessed based on their density: high-density foreign body in the posterior segment (probably, metallic; pink arrow), 80 - 550 HU density foreign body in the posterior segment (probably, glass; blue arrow) and low-density foreign body in the supraciliary region (aproximately between -100 and -200 HU; probably wooden; brown arrows); note the even lower density of air, around -1000 HU, in an intraocular air bubble (yellow arrow) and in the maxillary sinus (green asterisk). Abbreviations: axial view (AX), sagital view (SAG).

Fig 14: Pure and simple blow-out left orbital fracture; the orbital rim and internal orbital buttress (blue arrow) remain unaltered. > 50% of the medial orbital wall is involved (red square) and the fracture line extends up to < 1 cm from the optic canal (measurement in front of the magenta spot). While the right frontonasal duct appears to remain intact (right yellow arrows), the left one is hardly demarcated and permeable (left yellow arrow); its lesion should be suggested. The optic duct itself (magenta spot) and the superior and inferior orbital fissures remain unaffected. Regarding extraocular muscles, the left medial rectus (magenta arrow) and superior oblique (orange arrow) muscles look asymmetrical when compared to the contralateral ones; intraorbital fibrofatty tissue can also be spotted herniated into the ethmoid cells (dark green arrows), which also have hyperdense content compatible with haematoma (red arrow). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG).

Fig 15: Pure and simple blow-out left orbital fracture; the orbital rim and internal orbital buttress remain unaltered. > 50% of the orbital floor is involved (measurement in the lower left image) and the fracture line crosses the infraorbital canal (yellow circle). The left inferior rectus muscle (yellow arrow) looks asymmetrical when compared to the contralateral one and appears to be tractioned accompanying intraorbital fibrofatty tissue into the left maxillary sinus (dark green arrow); said sinus also has hyperdense content compatible with haematoma (red arrow). Abbreviations: coronal view (COR), sagital view (SAG).

Fig 16: Bilateral orbital blow-out fracture. The right internal orbital buttress is preserved, whereas a fracture line can be identified contralaterally (blue arrow in image a), thus making the left orbital fracture complex. Bilaterally, the fracture involves the medial orbital walls (green arrows in image b), the orbital floors (yellow arrows in image b) and both infraorbitary canals (yellow arrows in image c). Besides, the left lacrimal duct appears to be compromised (blue arrow in image d). Regarding intraorbitary structures, fat protrudes to left ethmoid cells and both maxillary sinuses (dark green arrows in image g) and morphological and directional asymmetries are notorious in several extraocular muscles: left medial rectus (magenta arrow in image f), both inferior rectus (yellow arrows in image g) and right superior rectus (blue arrow in image g). Lastly, retrobulbar haemorrhage signs (red arrow in image e) and various early signs of orbital compartment syndrome cannot go unnoticed: right optic nerve stretching (red arrow in image h), abnormal anterior and posterior globe-surface-to-interzygomatic-line distances (image i) and barely normal right posterior globe angle (image h). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), obliqued coronal view (OBL COR).

Fig 17: Left medial orbital wall fracture with globe lesion. The medial orbital wall is disrupted (red arrow in image a) and, thus, intraorbital fat and the medial rectus extraocular muscle protrude into left ethmoid cells (arrow in image b). In addition, the left “flat tyre” sign (red arrow in image c) and subluxation of the left lens (red arrow in image d) suggest traumatic left globe perforation (note the notorious asymmetry of said structures). Abbreviations: axial view (AX), coronal view (COR).

ZYGOMATICOMAXILLARY COMPLEX (ZMC) FRACTURES

The zygomatic bone is part of the orbit, the maxillary sinus and the zygomatic arch. Therefore, it has a characteristic tetrapod shape with 3 main pillars and 4 main sutures. Depending on the number of pillars fractured and the presence of comminution, the Zingg classification will vary (see "figure 18").

The presence of fragments' displacement and its direction could have great impact on intraorbital volume and mastication and, therefore, on the risk of enophtalmos, orbital apex syndrome, malocclusion and trismus (see "figure 18"); it should be consequently reported.

Fig 18: The upper left and the lower images show the 3 pillars and 4 sutures in the zygomaticomaxillary complex. Superiorly, the zygomatic bone is adjacent to the frontal bone (frontozygomatic suture) (purple line and arrows); medially, to the greater wing of the sphenoid bone in the lateral orbital wall (zygomaticosphenoid suture) (light orange line and arrows); anteriorly, to the maxillary bone (zygomaticomaxillary suture) (green line and arrow); and, laterally, to the temporal bone in the zygomatic arch (zygomaticotemporal suture) (red line and arrow). The 3 main pillars are the zygomatic arch (1 in upper left image), the anteromedial one, which is part of the orbital floor, inferior orbital rim and anterior and lateral walls of the maxilarry sinus, (3 in upper left image), and the upper one, which is part of the lateral orbital rim and wall (2 in upper left image). When a single pillar is fractured, the type Zingg A will apply; Zingg A1 if it is the zygomatic arch that is fractured, Zingg A2 when the upper pillar is damaged and Zingg A3 for anteromedial pillar fractures. Zingg B fractures require the involvement of every pillar of the zygomatic bone. Zingg C fractures are comminute. The upper middle and right images show the insertion of the masseter muscle in the zygomatic arch (right orange arrow) and in the coronoid process and ramus of the mandibular bone (left orange arrow); this is the reason for malocclusion and trismus risk after displaced zygomaticomaxillary complex fractures. Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG).

Fig 19: Right Zingg A1 zygomaticomaxillary complex fracture; the fracture is exclusively located in the zygomatic arch and zygomaticotemporal suture (red arrow) and acquires the typical angled shape due to its collapse (red angle). Abbreviations: volume rendering reconstruction (3D), axial view (AX).

Fig 20: Left Zingg C zygomaticomaxillary complex fracture; the fracture involves every zygomatic pillar and is comminute. Abbreviations: volume rendering reconstruction (3D), axial view (AX), coronal view (COR).

MAXILLARY OCCLUSION-BEARING (MOB) SEGMENT FRACTURES

MOB segment anatomy is describe in "figure 21". The following aspects define MOB segment fractures:

• These fractures can be incomplete (greenstick fractures; a single bone cortical is affected) or complete (both corticals are fractured, resulting in a separate fragment); both should be reported.
• The classification of Chen, et al is used for further description of hard palate fractures (see "figure 21").
• Dentoalveolar fractures must not be missed, as they are considered open fractures, with the consequent greater risk of infection.

Fig 21: The maxillary occlusion-bearing segment includes the maxillary sinuses (yellow inverted triangles), the piriform aperture (magenta oval), the nasal septum (magenta rectangle), the hard palate (yellow rectangle) and the alveolar rim (yellow outlining). Regarding the hard palate and according to the classification of Chen, et al, most fractures will acquire a sagital orientation (type I) (vertical multiangled red line), while fewer will take place in the axial or transverse plane (type II) (horizontal multiangled red line); comminute fractures are described as type III fractures.

Fig 22: Maxillary occlusion-bearing fragment fracture, that involves the anterior and lateral walls of the maxillary sinus (dotted horizontal arrows) and a type I hard palate fracture that extends to the alveolar rim (continuous white arrows). Abbreviations: axial view (AX), coronal view (COR).

LE FORT FRACTURES

Le Fort fractures are 3 specific patterns of midface fracture, whose compulsory common factor is the involvement of the pterygoid plates. Le Fort fractures can be either isolate or simultaneous, unilateral or bilateral, symmetric or asymmetric and complete (separate fragments) or incomplete (greenstick fractures).

Fig 23: The upper images emphasise the pterygoid plates (arrows), whose fracture is the common denominator in Le Fort fractures. The lower images show the different types of Le Fort fractures: type I or “floating palate” (red highlight and outline), type II or “floating maxilla” (blue highlight and outline) and type III or “craniofacial dissociation” (yellow highlight and outline). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D).

Fig 24: Le Fort type I fracture or “floating palate” (red highlight). Besides the pterygoid plates (filled green circle), it involves the anterior (4) and lateral (5) walls of the maxillary sinus and, specifically, its medial wall (3), the hard palate (1) and the nasal septum (2). Abbreviations: coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D). Colour codes: specific fractures (red circle).

Fig 25: Le Fort type II fracture or “floating maxilla” (blue highlight). Besides the pterygoid plates (filled green circle), it involves, in an anteroposterior direction, the nasal bones (1), the orbital medial wall and, specifically, the orbital floor (2), and the anterior (3), medial (4) and lateral (5) walls of the maxillary sinus. Abbreviations: axial view (AX), sagital view (SAG), volume rendering reconstruction (3D). Colour codes: specific fractures (red circle).

Fig 26: Le Fort type III fracture or “craniofacial dissociation” (yellow highlight). Besides the pterygoid plates (filled green circle), it involves, in a mediolateral direction, the nasal bones (1), the orbital medial wall (2) and, specifically, the orbital lateral wall (3) and the zygomatic arc (4). Abbreviations: coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D). Colour codes: specific fractures (red circle).

Fig 27: Multiple Le Fort fractures: bilateral Le Fort type I (red lines in images a and b) and type II (blue lines in images a and b) fractures and right Le Fort type III fracture (yellow lines in images a and b). Pterygoid apophyses are fractured bilaterally (arrows in image c). Le Fort type III fracture extends along nasal root / frontonasal suture (arrow in image d), medial and, characteristically, lateral orbital walls (arrows in image e) and, specifically, the zygomatic arch (arrow in image f). Le Fort type II fracture is defined by disruption of nasal bones / root (arrow in image d), medial wall (green arrow in image g) and, especially, orbital floor (blue arrows in image g), and anterior and lateral maxillary sinus’ walls (green arrows in image h). Le Fort type I fracture encompasses, particularly, the nasal septum (red arrow in image g), anterior, lateral and, characteristically, medial maxillary sinus’ walls (green and red arrows in image h) and, quite specifically, the hard palate (arrow in image i). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D).

FACIAL FRACTURES: LOWER THIRD

MANDIBULAR FRACTURES

Mandibular bone anatomy is explained in "figure 28". Due to its shape, the mandibular bone will frequently develop two different fractures, a primary one at the area of direct trauma, and a secondary contralateral one due to force transmission. 

CT-based predictors of malocclusion should be reported:

• Condyle fracture or luxation: see "figure 28". Condyle fracture also entails greater risk for temporomandibular joint dysfunction.
• Regarding subcondylar fractures:
  • Fragment angulation > 35º.
  • Ramus shortening > 15 mm.
  • Severe bilateral posterior vertical height loss.

The mandibular canal's condition, the presence of basal triangles (see "figure 28") and dentoalveolar fractures should be reported, as surgical fixation may be necessary.

Fig 28: The mandibular bone, highlighted in the upper left image, is responsible for facial shape, mastication and speech and is composed of 2 vertical units, 2 horizontal ones and a central anterior binding component. The vertical units are formed of the condyle (head, neck and subcondylar region) (Cd; light blue), the coronoid process (Cr; light red), the ramus (R; green) and the mandibular angle (A; yellow). The horizontal units are equivalent to the mandibular body (Cu; dark blue) and the central anterior binding ones to the symphyseal and parasymphyseal regions (S; orange). The upper rim of the mandibular body and the central binding unit is the alveolar process (Av; magenta), and the lower rim of said parts and of the mandibular angle, the basal segment (B; purple). The upper right image highlights the lateral pterygoid muscles (orange rectangles), which are attached to the mandibular condyle and to the lateral pterygoid plate; therefore, in the trauma context, a fracture could take place in the condyle itself (due to said muscle insertion, the condyle fragment will almost always be anteromedially and inferiorly displaced) or in the lateral pterygoid plate (the condyle remains intact, but, the lateral pterygoid muscle it is linked to, provokes an avulsion fracture of the lateral pterygoid plate). The mandibular canal (curved rectangle) carries the inferior alveolar nerve (branch of the cranial nerve V3), that provides sensory innervation to the lower teeth and gums; it runs from the upper inner mandibular foramen in the ramus (asterisks), to the lower outter mental foramen in the body (filled circle). This canal should be assessed and its content’s lesion suggested when fractured and, more emphatically, when the fracture accross the canal is accompanied by > 5 mm displacement of fragments. The yellow arrow in the upper centre image, points at a basal triangle; it is a separate fracture fragment, usually secondary to a vertically expanded dentoalveolar fracture, that compromises stability and, thus, requires surgical fixation. Abbreviations: axial view (AX), volume rendering reconstruction (3D).

Fig 29: The images on the left side of the vertical white bar show a bilateral mandibular fracture. The left fracture (camel arrows) is located in the mandibular angle and crosses the mandibular canal, causing a > 5 mm fragment displacement (measurement in lower right image). The nondisplaced right fracture (light orange arrows) is subtle in the parasymphyseal region, but appears to involve the mental foramen. The images on the right side of the vertical white bar illustrate a bifocal left mandibular fracture. A comminute and displaced (lower right image) fracture involves the symphyseal and parasymphyseal regions (light orange arrows) and the mandibular body (darker blue arrows) and crosses the mental foramen of the mandibular canal. The other fracture is a subcondylar luxation-fracture (lighter blue arrows) with > 35º angled fragments (light blue angle). Abbreviations: axial view (AX), coronal view (COR), sagital view (SAG), volume rendering reconstruction (3D).