Image Interpretation Course

by Heidi Nunn DCR(R) PgCert

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The Facial Bones  

Facial Bones Projections

Occipito-mental View

• The PA occipito-mental view provides excellent demonstration of the upper and middle thirds of the face including the orbital margins, frontal sinuses, zygomatic arches and maxillary antra:
  
  


Occipito-mental 30 View

• With 30 degrees of caudal angulation, the orbits are demonstrated less well. However, the zygomatic arches and the walls of the maxillary antra are seen clearly:
  
  

Three lines for inspecting the OM views

   
Line 1:
• Look for widening of the zygomatico-frontal sutures
• Fractures of the superior rim of the orbits
• “Black-Eyebrow” sign due to orbital emphysema
• Opacification / air-fluid level in the frontal sinuses
  
  Line 2:
• Look for fractures of the superior aspect of the zygomatic arch
• Fractures of the inferior rim of the orbits
• Soft tissue shadow in the superior maxillary antrum
• Fractures of the nasoethmoid bones and medial orbits

Line 3:
• Look for fractures of the inferior aspect of the zygomatic arch
• Fractures of the lateral maxillary antrum
• Opacification / air-fluid level in the maxillary sinuses
• Fractures of the alveolar ridge

Compare the injured side with the uninjured side.

Fractures of the Facial Skeleton

• Within the facial skeleton, there are relative areas of strength, which tend to be spared by fractures lines. These are:

Alveolar ridge of the maxilla
Nasofrontal process of the maxilla
Body of the zygoma

Fractures of the Orbits

• Blow out fracture

  The most common portion of the orbit to sustain a fracture is the weak floor, and this injury, if occurring in isolation, may result in a blow-out fracture. A blow to the globe causes increased intraorbital pressure. This causes a fracture of the thin plate of bone forming the floor of the orbit (i.e., the roof of the maxillary antrum). Some of the orbital contents such as fat and muscle herniate downwards into the maxillary sinus resulting radiographically in a soft tissue “teardrop”, or polypoid mass, in the roof of the maxillary antrum:
  

  
• Orbital emphysema

  Herniation through the medial wall may also occur. Air from the maxillary or ethmoid sinuses may enter the orbit, giving rise to orbital emphysema. This is commonly known as the “black eyebrow” sign:

     

Fractures of the Zygoma

• Tripod fracture

  The zygomatic bone has three distinct limbs; the orbital process leading to the zygomatico-frontal suture, the zygomatic arch and the maxillary process surrounding the superior and lateral margins of the maxillary antra. Trauma to the facial skeleton tends to spare areas of relative strength, and the body of the zygoma is one such area. It therefore follows that fractures are likely to be sustained at these three limbs and such an injury is termed the tripod fracture.

Radiographically, this common injury manifests itself as:

• Widening of the zygomatico-frontal suture.
• Fracture of the zygomatic arch.
• Fracture of the inferior orbital rim extending through the anterior and lateral walls of the maxillary antrum.
  
  
   

Both the OM and OM 30 views will identify these fractures, along with the associated soft tissue swelling over the zygomatic eminence and opacification or an air-fluid level in the maxillary sinus. Often only a straight PA would identify the diastasis at the zygomatico-frontal suture.

• Isolated fractures of the zygomatic arch

  These generally consist of three fracture lines with medial and inferior displacement of the fragments. More often than not, however, an apparently isolated fracture of the zygomatic arch is actually part of a more complex tripod fracture.

  

Fractures of the Maxilla

• The classification of maxilla fractures again follows the concept of areas of relative strength within the facial skeleton. There are three principal fracture lines which correspond to relative areas of weakness, and these are referred to as LeFort fractures. By definition, these fractures must transect the pterygoid process of the sphenoid bone.
  
  

LeFort I

This is a transverse fracture through the inferior maxillary antra, which separates off the alveolar process of the maxilla. The LeFort I is demonstrated on the OM view with fractures through the medial and lateral walls of the maxillary antra, and the nasal septum.

LeFort II

This is a pyramidal fracture, which separates off the central portion of the face. The OM film identifies the LeFort II with fractures through the lacrimal bones, medial orbital walls, infra-orbital rim and lateral walls of the maxillary antra.

LeFort III

This fracture is characterised by separation of the entire facial skeleton from the skull. The posterior aspect of the fracture extends down the posterior maxillary sinus walls. Fracture lines will be visible on the OM view extending from the medial orbits and nasoethmoid region across the ethmoids posteriorly. The orbits appear elongated with wide diastasis of the zygomatico-frontal sutures, or fractures of the orbital process of the zygoma.

In practice, this classification is over-simplified, and in reality, fractures tend to be more complex. There may be a combination of appearances, such as a LeFort II on one side, and a LeFort III on the other. Also, as these injuries are associated with major trauma, these patients tend to go direct to CT and plain film examples of classic LeFort fractures are infrequent.

Mandibular Projections

Orthopantomogram (OPG)
• This is an excellent method of demonstrating virtually all mandibular fractures, including the coronoid and condylar processes. Be aware however; occasionally symphysis menti fractures may not be seen.
  
  
  

Posteroanterior (PA) Mandible
• The OPG must be supplemented with a PA mandible to establish displacement of fractures. This will demonstrate the body and symphysis menti, and also provide tangential views of the rami and the necks of the condyles:
  
  
  

Lateral obliques
• In the absence of an OPG, the lateral obliques will demonstrate the body and ramus on each side. The articulation at the temporomandibular joint may also be assessed:
  
  
     

Fractures of the mandible

• The distribution of fractures of the mandible are:

• Fractures of the mandible tend to occur in more than one place, therefore once one has been identified, another should be sought. The second injury may be a fracture, or a temporomandibular joint dislocation.
• The mandible is composed of an inner and outer cortex enclosing the medullary cavity. Fracture lines may be identified at the both inner and outer cortices but this represents one fracture:
  
  
  
• Air in the pharynx may also be identified on the OPG overlying the condyle and ramus. This should not be mistaken for a fracture.
• Fractures of the coronoid and condylar processes often occur at their bases and may be difficult to visualise. The PA mandible will demonstrate medial (or less commonly lateral) angulation of the condyle by the pterygoid muscle:
  
     
• Fractures are classified as either favourable or unfavourable. A favourable fracture is one that is held in apposition and alignment to the natural pull of the attached muscles. Unfavourable fractures are those that are displaced by the pull of attached muscles.
• After diagnosing a fracture, it is important to identify any pathological dental condition in which the fracture lies. This is best demonstrated on the OPG. A fracture that extends into a periapical abscess may result in delayed healing and osteomyelitis.

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