Education and debate BMJ 1994;308:46-50
(1 January)
ABC of Emergency Radiology: Maxillofacial Radiographs
D W Hodgkinson, R E Lloyd,
P A Driscoll, D A Nicholson
This article deals with the problems facing non-specialist
doctors requesting emergency radiographs of facial bones.
An appropriate history and clinical examination will lead
to suspicion of maxillofacial trauma and other pathology.
We describe a systematic approach to requesting and
interpreting maxillofacial views.
Important anatomy
Knowledge of the normal anatomy and radiological appearance
of the skull is essential to interpreting radiographs of the
face (see article on skull, 4 December,pp 1476-81).
The face can be divided into three areas: the upper third -
area above the superior orbital margin; the middle third -
area between the superior orbital margin above and the
occlusal plane below; and the lower third - the lower jaw
(mandible). Standard radiographic investigation of the
face is describe with reference to these three areas.
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FIG 1 - Lateral
radiograph with line drawing showing radiological
anatomy. |
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Mechanism of injury
The mechanism of injury is an important aid to identifying the
specific injury and any possible associated injuries. It can
help decide which type of film to request and the urgency of
the request. Isolated injuries to the maxillofacial skeleton
commonly result from an assault. More severe injuries occur
after high energy transfer (for example, road traffic
accidents) and may be associated with injuries to the
head, neck, chest, and other body regions.
Good quality, carefully positioned radiographs are required.
This can be difficult to achieve in patients presenting to the
emergency department (because of multiple injuries or alcohol
intoxication). Poor quality and incorrectly positioned films
must not be accepted. Radiology of a clinically suspected
maxillofacial injury can often be delayed until the
patient is more cooperative or good quality films can be
taken.
The standard radiographic projections are listed below. Each
projection provides only a limited amount of information and
several views are therefore required to assess an injury
fully. The clinical findings should be used to determine
the probable site of injury and dictate which views are
most appropriate.
Radiographic projections
Appropriate radiographic views for detecting trauma to
maxillofacial regions
Anatomical sites Clinical findings Radiographic views.
Upper third:
Nasoethmoid Periorbital haematoma, epistaxis, Occipitofrontal
displaced nasal bones, deviated and lateral
nasal septum, cerebrospinal fluid
rhinorrhoea, transverse cleft in
glabellar region
Orbits Diplopia, enophthalmos, proptosis, Occipitofrontal
restriction of ocular movements and lateral
Middle third:
Zygomatic Periorbital oedema, haematoma, Occipitomental 45
complex infraorbital anaesthesia, step
deformities/flattening of the cheek
Zygomatic Depression over arch, restriction Submentovertical
arch of mandibular movement
Maxilla Occipitomental
LeFort 1 Swelling of upper lip and cheek, Occipitomental
mobile maxilla, teeth gagged and lateral
posteriorly
LeFort 2 and 3 Facial oedema (severe in 3), Occipitomental 45
periorbital haematoma, elongation of and lateral
face (dished), mobile maxilla, teeth
gagged posteriorly
Lower third:
Mandible Tenderness; bruising, swelling; Orthopantomogram
bleeding from mouth or ear, or and posteroanterior
both; anaesthesia of lower lip; or Towne's, lateral
crepitus or mobile fracture; oblique, and
malocclusion or inability to posteroanterior
close the teeth
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Radiological investigation of non-traumatic maxillofacial emergencies
Diagnosis Clinical findings Radiographic view
Periapical Facial pain or swelling Orthopantomogram
abscess
Sinusitis Facial pain, swelling, or tenderness Occipitomental 45
(maxilla)
Nasal discharge Occipitofrontal
(frontal/ethmoid)
Sialadenitis Acute pain after eating Posteroanterior
Swelling of salivary gland Lateral obliques
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Occipitomental projection (45° and 30°) - These views
are used to assess the maxilla (LeFort 1,2, and 3 fractures),
the zygomatic complex, and orbital floor
View larger version (144K):
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FIG 2 -
Occipitomental 45 radiograph with line drawing. The drawing
also shows the five lines that should be traced when
assessing the radiograph. |
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The lateral projection (fig 1) is used to assess all three parts
of the face. It can be taken with the patient lying supine on
the table with a portable unit (unlike the other projections).
Occipitofrontal projection (25°) - This is used to assess
the upper third of the face and orbits. The view projects the
top edge of the petrous bones just below the infraorbital
margins and thus shows the whole of the orbits.
The submentovertical projection is used to assess the
zygomatic arch.
The orthopantomogram is used to assess the mandible. It is
very informative but requires the cooperation of the
patient because of the long exposure time. It is
replacing the lateral oblique view as the best method of
assessment.
Posteroanterior projection(10°) - This is used to assess
the mandible.
Towne's view shows the ascending rami of the mandible and
the condyles on each side.
Lateral oblique projection - These views are valuable for
assessing the body of the mandible.
Nasal bones
A simple nasal bone fracture is diagnosed clinically and
routine radiography of the nasal bones is unnecessary.
Trauma to the bridge of the nose may produce a
nasoethmoid fracture. These patients usually have
persistent epistaxis or cerebrospinal fluid rhinorrhoea,
or both. This injury cannot be excluded by plain
radiographs.
Temporomandibular joint projection
These specialised views should be requested only when specific
information about the function of the joint is required.
Non-specialists should not need to request or interpret
these views. Fractures of the mandibular condyle are
common and are diagnosed with other views. They rarely
affect the temporomandibular joint except when the
condyle and the glenoid fossa are fractured together in
high energy trauma.
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FIG 3 - LeFort
lines used for classifying fractures of the middle
third of the face. |
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FIG 4 -
Submentovertical view showing a fractured zygomatic arch.
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FIG 5 - The
positioning of the patient, the xray source, and the
film for (from left to right) the occipitomental 45,
submentovertical, and Towne's views. The base
line is the line drawn between the external
auditory meatus and the orbit. |
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Radiological assessment of occipitomental view
Radiographs should be interpreted by using the ABCs system.
Adequacy and quality of the radiograph
Start by identifying the name of the patient and the date on
which the radiograph was taken. Then ensure that it is
correctly centred by tracing a line that connects the
nasal septum, the centre of the mandible, and the
odontoid peg. This should be vertical, straight, and run
through the centre of the film. Next look for rotation by
tracing the outline of the orbits; they should be the
same size and shape and the lateral walls should be of
equal thickness and equidistant from the nasal septum.
Another method of assessing rotation is to draw the
imaginary Campbell line 2 (see below) and look for rotation
of the orbits about a vertical and horizontal axis.
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FIG 6 -
Occipitomental view showing fractured zygoma. Note the
increased size of the left orbit and
opacification of the left maxillary sinus. |
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View larger version (65K):
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FIG 7 -
Occipitomental view showing a LeFort 2 fracture. Fractures
are visible on both sides (arrows). The opacification
of both maxillary sinuses and the general hazy
appearance of the film is consistent with severe
soft tissue swelling. |
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FIG 8 -
Occipitomental view showing a fractured zygomatic bone
complex and line drawing showing disruption of
all four legs of the stool (arrows). |
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Alignment and bones
Figure 2 shows the five lines that should be traced when
assessing the radiograph. They are known as Campbell's
lines.
Line 1 joints the two zygomaticofrontal sutures. It runs
along the superior orbital margin on each side and
centrally across the region of the glabella. Check for
any separation of the zygomaticofrontal suture and look
at the integrity of the superior orbital margins.
Line 2 is traced from the zygomatic arch. It follows the
zygomatic bone and continues along the inferior orbital
margin across the frontal process of the maxilla and
lateral wall of the nose through the septum. It then
follows a similar course on the other side. Check the
zygomatic arch for fractures then compare the transverse
width of the frontal process of the maxilla and vertical
dimensions of the zygomatic bones on the left and right
side. Any asymmetry may indicate a fracture. Look for a break
in continuity of the inferior orbital margin, particularly at
the junction of the inner third and outer two thirds. A
downward blow out fracture of the orbit may be seen (tear
drop sign), but this is not a consistent feature in this
injury.
Line 3 starts at the condyle of the mandible and traces
across the mandibular notch and coronoid process to the
lateral wall of the maxillary antrum. It continues
through the medial wall of the antrum or lateral wall of
the nose at the level of the nasal floor and then follows
a similar course on the opposite side. Check the
continuity of the maxillary antral walls and look for any
depression of the orbital floor.
Line 4 follows the occlusal curve of the upper and lower
teeth. Check for evidence of mandibular fractures,
although the definition may be poor and specific views
are required for detailed assessment.
Line 5 traces the line of the lower border of the
mandible. Check the continuity of this line.
Cartilages and joints
Look at the separation of the zygomaticofrontal suture located
on line 1 above. Look for asymmetry between the two sides. The
joint space should be smooth and thin, symmetrical along its
length, and uninterrupted.
Sinuses
Check all the paranasal sinuses, in particular the frontal,
maxillary, and ethmoid. Trace the outline of each sinus and
look for any asymmetry between each side. Look for
opacification of the sinus (complete or partial). If a
fluid level is suspected within the sinus the patient
should have a brow up lateral projection. The orientation
of the patient and therefore the air fluid level will
differ in the two views.
Discontinuity in the margins of the sinus indicates a fracture.
Soft tissue
Check the soft tissues by using a bright light. The soft
tissue shadow from the line of the cheek can be seen
traversing the orbit. If excessive swelling is present on
one side the maxillary antrum on the same side may appear
more radio-opaque. Look for a tear drop appearance in the
top of the maxillary antrum. This may represent a blow
out fracture of the orbital floor in the correct clinical
context.
Check for foreign bodies within the soft tissues. Some objects
(for example, glass) can be difficult to see without a bright
light.
Indirect signs of maxillary fracture
* Soft tissue swelling
* Opacification of the maxillary sinus is usual in fractures
which affect its wall and an air-fluid level is usually seen
* Soft tissue emphysema is a rare but useful sign. It provides
positive evidence of a fracture of the nasal cavity or one of the
paranasal sinuses. It may show as multiple small radiolucent areas
in the soft tissues. Alternatively air may enter the orbit to
outline the eyeball
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Important rules and diagnostic traps
Middle third of face
The zygomatic bone complex can be compared to a four legged
stool with the legs being represented diagrammatically as: the
floor of the orbit, the lateral wall of the orbit, the
zygomatic arch, and the lateral wall of the antrum. The
seat of a stool cannot be displaced without moving at
least two of the legs. Likewise it is not possible to
displace the zygomatic bone without fracturing two of the
legs. Thus if one leg is thought to be fractured the
other three must be checked.
Lower third of the face
When the mandible is injured it behaves as if it were a complete
ring. This is because it is rigid and connected at each end
of the skull by a firm joint. If one fracture of the mandible
is found in the radiograph another fracture or dislocation is
present. Fractures of the angle of the mandible on one side
are commonly associated with fractures through the mandibular
condyle on the opposite side.
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FIG 9 -
Occipitomental view showing air-fluid level in the left
maxillary sinus. Note tear drop sign projecting into
the roof of the sinus (see line drawing). This is
a feature of a downward blow out fracture of the
orbit. |
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FIG 10 -
Orthopantomogram showing fracture through the angle of
the mandible on the left side and a subtle fracture
through the body on the right side (arrow). |
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Normal anatomical structures can sometimes be mistaken for
fractures. There are four common sites:
* Air in the oropharynx at the angle of the mandible. If checked
carefully this line will extend beyond the outer cortex of the
mandible
* Calcification or ossification of the stylohyoid ligament
projecting over or just behind the ascending ramus
* The hyoid bone shown over the posterior part of the horizontal
ramus
* The intervertebral spaces of the upper cervical vertebrae
overlying the maxillae, simulating a LeFort 1 fracture, or
over the mandibular symphysis, mimicking a dentoalveolar
fracture.
Fractures of the mandible, particularly at the angle and the
condyle, can appear undisplaced when seen in only one view.
At least two views at right angles to each other are essential
for full assessment - posteroanterior, Towne's, or lateral
oblique.
The anterior mandible can be difficult to see in the
orthopantomogram and lateral oblique projection because
of superimposition of other structures. A lower occlusal
view of the anterior mandible may therefore be useful in
certain situations.
Summary
Adequacy
Alignment
Check lines 1-5
Bones
Cartilage and joints
Zygomaticofrontal suture
Sinuses
Opacification
Air-fluid levels
Soft tissue
Swelling
Foreign bodies
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D W Hodgkinson is lecturer in emergency medicine, R E Lloyd
is consultant maxillofacial surgeon, P A Driscoll is senior
lecturer in emergency medicine, and D A Nicholson is
consultant radiologist, Hope Hospital, Salford.
The line drawings were prepared by Mary Harrison, medical
illustrator.
The ABC of Emergency Radiology has been edited by David Nicholson
and Peter Driscoll.
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