Facial Bones

FACIAL BONES

These are the bones which form the face.

These are composed of the maxilla (upper jaw), the nasal, lacrimal, vomer, palatine and zygomatic bones and the mandible.

The mandible is mostly examined separately.

ANATOMY

The facial skeleton is complex and the series of images produced are difficult to assess radiologically for diagnosis; optimal projections are therefore extremely important. The facial bones are a series of 14 irregular bones that collectively are attached to the antero-inferior aspect of the skull. Within these bones, and some of the bones forming the cranial base, are a series of air-filled cavities known as the paranasal air sinuses.

Facial Bones

These communicate with the nasal cavity and the margins of them appear of higher radiographic density than surrounding bones, as the air within them offers little attenuation to the X-ray beam. If the sinuses become filled with fluid due to pathology, e.g. blood in trauma or chronic infection, this results in a decrease in radiographic density and increase in radio-opacity.

The sinuses are therefore best imaged by using a horizontal beam, with the patient in the erect position thus demonstrating fluid levels.

Facial Bones

Maxillary sinuses (maxillary antra): paired, pyramidal shaped structures located within the maxillary bone either side of the nasal cavity. These are the largest of the sinuses.

• Frontal sinuses: these are paired structures located within the frontal bone adjacent to the fronto-nasal junction (acanthion).

They are very variable in size and shape and in some individuals they may be absent.

• Sphenoid sinus: this structure lies immediately beneath the sella turcica and posterior to the Ethmoid sinuses.

• Ethmoid sinuses: a labyrinth of small air spaces that collectively form part of the medial wall of the orbit and the supero-lateral walls of the nasal cavity

Radiological considerations

The facial bones and sinuses are complicated structures and the radiographer must be aware of their anatomical position and radiographic appearances in order to assess the diagnostic suitability of an image.

The accompanying diagrams and radiographs outline the position of the major structures and landmarks used for image assessment. If serious facial injury is suspected clinically, CT will give more detailed information, with the ability to perform 3D reconstructions.

Facial Bones

Due to the complexity of facial fracture patterns there are some well-known fracture classifications and assessment models to allow radiographers and clinicians viewing/reporting upon plain facial images to demonstrate the severity and involvement of the facial skeleton.

Assessment tools

McGrigors’ lines are lines on the facial skeleton that can be followed to exclude or confirm any breach in continuity and thus a facial fracture.

The lines are visible on any OM image.6 Follow all 3 lines:

• Line 1: fronto-zygomatic suture across the superior orbital margin, nasion and opposing side.
• Line 2: superior aspect of zygomatic arch, frontal process of zygoma, inferior orbital margin, nasal bones and opposing side.
• Line 3: inferior aspect zygomatic arch, base of maxillary sinuses, maxilla at base of upper teeth and opposing side.

The basic views

• Occipito-mental (OM)
• Lateral

OM 30⁰ caudad

The examination of the facial bones is guided by the indication of the examination.

The above routine views are for the general facial radiographs but depending on indication, views likeTowne’s view may be included.

Occipito-mental (OM) (chin nose) view

This projection shows the orbits, nasal region, the maxillae and the zygomatic bones.

Positioning the patient

The patient is preferably seated facing an erect-Bucky but the examination can be carried out with the patient lying prone on the Bucky table if necessary.

The patient’s nose and chin are in contact with the mid-line of the Bucky and then the head adjusted to bring orbito-meatal line at 45⁰ to the central ray directed perpendicular to the film.

Facial Bones

Centre:- towards the mid-line at the level of the lower border of the orbits with the central ray perpendicular to the film.

Essential image characteristics (Figs 8.28b, 8.28c)

• The petrous ridges should be demonstrated inferior to the floors of the maxillary sinuses.
• There should be no rotation. This can be checked by ensuring the distance from the lateral orbital wall to the outer skull margins is equidistant on both sides.

Facial Bones

In case of injury to the face, better results may be obtained by raising the chin still further so that the central ray makes an angle of 60⁰ with the mid-line.

As this tilt is too great for the patient to attain the tube placed high and tilted towards the feet i.e tilt the Orbito-meatal line 40⁰ and tilt the tube 20⁰ Centre as before.

Occasionally accident cases are unable to lie prone and film can be taken in the reverse direction (Mento-Occipital). The patient is supine the OM line 65⁰ to the film, tube tilted approximately 20⁰ so that the incident beam makes an angle of 45⁰ with the Orbito-meatal line.

Centre over the mouth

Common faults and solutions

• Petrous ridges superimposed over the inferior part of the maxillary sinuses. In this case several faults may have occurred. The orbito-meatal baseline may not have been positioned at 45° to the cassette/receptor; a 5–10° caudal angulation could be applied to the tube to compensate for this.
• As this is an uncomfortable position to maintain, always check the baseline angle immediately before exposure.

LATERAL

• In cases of injury, this projection should be taken using a horizon-
• tal beam in order to demonstrate any fluid levels in the paranasal

sinuses. The patient may be positioned erect or supine.

Position of patient and cassette

Erect

• The patient sits facing the vertical Bucky or cassette holder of the skull unit. The head is rotated, such that the side under examination is in contact with the Bucky or cassette holder.
• The arm on the same side is extended comfortably by the trunk, whilst the other arm may be used to grip the Bucky for stability. The Bucky height is altered, such that its centre is 2.5 cm inferior to the outer canthus of the eye.

Supine

• The patient lies on the trolley, with the arms extended by the sides and the median sagittal plane vertical to the trolley top.
• A gridded cassette is supported vertically against the side under examination, so that the centre of the cassette is 2.5cm inferior to the outer canthus of the eye.

Direction and centring of the X-ray beam

• Centre the horizontal central ray to a point 2.5 cm inferior to the outer canthus of the eye.

Essential image characteristics

• The image should contain all of the facial bones sinuses, including the frontal sinus and posteriorly to the anterior border of the cervical spine.
• A true lateral will have been obtained if the lateral portions of the floor of the anterior cranial fossa are superimposed.

Lateral:

In cases of injury, this view must be taken using a horizontal beam in order to demonstrate any fluid level in the paranasal sinuses.

Positioning:- in lateral view of the face, the head is placed in lateral position with the greatest care.

Centre:- over the zygomatic bone, collimate just to cover the area required.

ZYGOMATIC ARCHES

A modified Towne’s view gives a good views of the zygomatic arch.

The position of the patient and 30⁰ tilt is unchanged but the tube is moved a little towards the feet so that the central ray passes through the glabella instead of through the hairline.

The film should be placed so that its centre point lies at the level of the chin Other views of the zygomatic arch are laws projection done on mastoids and lateral may also be seen in the lateral oblique view for the mandible.

NASAL BONES

To show nasal bones in the lateral view a soft tissue film of the face may be obtained in the cassette by placing a second film in front of the intensifying screens.

But if the nasal bones are only being examined use an occlusal film Positioning:- the head is placed in a true lateral position. The FFD is increased to compensate for the increased object film distance.

A view at right angles to this is obtained by using:-

OM view

Supero-inferior view using an occlusal film placed in the mouth between teeth. The tube is above the head and centre to the root of the nose. The nasal bones may be slightly obscured by the frontal bone.

MANDIBLE

The mandible is composed of a central, curved part called the body and two ascending rami.

• In the centre of the body is the symphysis menti.
• It is a common site for fracture.
• Basic views
• Postero-anterior (PA)

Lateral oblique

Postero-anterior (PA)

The patient is in a prone position, the mid plane at right angle with the cassette, the RBL also perpendicular to the table.

Centre: In the midline 5 cms below the radiographic baseline.

Lateral oblique

The patient is positioned as for lateral skull with side to be examined nearer to the cassette.

Centre: 5 cms below the angle of mandible nearest the x-ray tube with tube angled 25⁰-30⁰ towards the head.

Additional view

Pan-oral tomography:

In this view the anterior mandible will be demonstrated without the cervical spine being superimposed

TEMPORAL-MANDIBULAR JOINTS

BASIC VIEW;

lateral 25 degrees caudad

-It is usual to examine both temporal-mandibular joints. For each side, a projection is obtained with the mouth open as far as possible and then another projection with the mouth closed.

An additional projection may be required with the teeth clenched.

Position of the patient and cassette The patient sits facing the vertical Bucky or skull unit cassette holder or lie prone on the Bucky table. In all cases, the head is rotated to bring the side of the head under examination In contact with the table

Facial Bones

The head and Bucky or cassette holder level is adjusted so the Centre cross-lines are positioned to coincide with a point 1cm along the orbito-meatal baseline anterior to the external auditory meatus.

The median sagittal plane is brought parallel to the cassette by ensuring that the inter-pupillary line is at right- angles to the table top and nasion and external occipital protuberance are equidistant from it.

Facial Bones

The cassette is placed longitudinally in the cassette holder, such that two exposures can be made without superimposition of the image

DIRECTION AND CENTERING OF THE X RAY BEAM

-using a well collimated beam the central ray is angled 25 degrees caudally and will be centered 5cm superior to the joint remote from the cassette so the central ray passes through the joint nearer the cassette.

Facial Bones

TMJ images are useful in assessing joint dysfunction by demonstrating erosive and degenerative changes. Open-closed mouth projections can be very helpful in assessing whether normal anterior grinding movement of the mandibular condyle occurs on jaw opening.

Paranasal sinuses

Plain images of the sinuses are unreliable for diagnosis of inflammatory sinus disease, since many asymptomatic people will have sinus opacification and sinus symptoms may be present in the absence of gross sinus opacification. Acute sinusitis (especially infective) may manifest radiologically as fluid levels in the maxillary antrum, but it is questionable as to whether this alters clinical management. Malignant sinus disease requires more comprehensive imaging by computed tomography (CT) and/or MRI. Some radiology departments will no longer perform plain sinus radiographs.

Occipito-mental

• This projection is designed to project the petrous part of the
• temporal bone below the floor of the maxillary sinuses so that

fluid levels or pathological change

Position of patient and cassette

• The projection is best performed with the patient seated
• facing the skull unit cassette holder or vertical Bucky.
• The patient’s nose and chin are placed in contact with the
• midline of the cassette holder. The head is then adjusted to
• bring the orbito-meatal baseline to a 45-degree angle to the
• cassette holder.
• The horizontal central line of the Bucky or cassette holder
• should be at the level of the lower orbital margins.
• Ensure that the median sagittal plane is at right-angles to the
• Bucky or cassette holder by checking that the outer canthi of
• the eyes and the external auditory meatuses are equidistant.
• The patient should open the mouth as wide as possible
• before exposure. This will allow the posterior part of the

sphenoid sinuses to be projected through the mouth.