Radiography: skull (basic)

• Radiography of the skull requires general anesthesia. This is the only way to obtain accurate projections.
• A grid is not necessary.
• Radiography of the skull for fractures may be of questionable value as the presence of a fracture is considerably less significant than the presence of neurological signs. It may, however, in some cases, be of value in explaining the reason for the signs when trauma is a possibility but has not been observed.
• When using non-screen film for intraoral radiography the increase in exposure required is immense. It is therefore necessary to ensure that the equipment is adequate, that the finger is not removed from the exposure button before completion of the exposure, and, most importantly, that staff do not re-enter the room before termination of the long exposure.
• The objective is to produce well-positioned radiographs which are correctly exposed and developed, free from movement blur and free from artifact.
• The anatomical marker, the patient's identification, the date, and the name of the hospital or practice should be clearly shown.

• Soft tissue neoplasia, eg nasal tumors  .
• Bulla disease
• Temporomandibular joint disease.
• Fracture.
• Bony neoplasia    .
• Hydrocephalus.
• Nasal foreign body.
• External ear disease  .

Advantages

• Non-invasive (although may require GA).

• In patients with neurological signs there is often nothing to be gained by X-raying the skull as it is the brain which needs to be imaged.
• Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) are the modalities of choice for most brain imaging, where these are available.

Preparation

• Dependent upon the method of chemical restraint (GA or sedation).

Procedure

• 10 to 15 minutes, or longer, dependent upon skill of radiographer.

Criteria for choosing test

Is the examination appropriate?

• Can you make the diagnosis without it?
• Can it tell you what you need to know? This is often not the case with skull radiography!
• Will your management be affected by the radiological findings?

Choosing the right projection

Lateral

• Standard projection  .
• May show gross fractures, depending on their position.
• May show skull vault shape abnormalities.
• Will give some information about the nasal chambers and frontal sinus, notwithstanding the fact that the two sides are overlying each other.
• May show neoplasms involving the bone.

Dorsoventral

• May give information on skull vault shape.
• May show gross fractures, depending on their position.
• Good for fractures of the zygomatic arches.
• Good for some mandibular fractures and dislocation of the temporomandibular joints.
• Of some use for tympanic bullae.

Lesion orientated obliques

• For suspected depressed fractures and for lumps on the skull the best projection is often an oblique, positioned so that the beam passes tangentially across the lesion or area of interest     .

Intraoral dorsoventral nasal chambers

• This is preferable to the alternative ventrodorsal open mouth nasal chambers.
• It gives a high resolution image of both sides of the nasal cavity and the radiological appearances can advance the diagnosis of nasal pathology considerably.
• Dental non-screen (direct exposure) film is necessary for this technique.

Other involvement

• Radiographer, or Technician carrying out radiography.

Minimum equipment

• X-ray machine.
• Cassettes with high definition screens.
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges, blocks.
• Protective clothing (lead-rubber aprons).
• For the intraoral nasal view, non screen (direct exposure) film is required.
  Dental occlusal film is suitable.

Ideal equipment

• High output X-ray machine.
• Rare earth high definition screens.
• Automatic processing facilities.

Minimum consumables

• X-ray film.
• Pharmaceuticals for anesthesia.

• One to two competent people.
• Sandbags.
• Foam wedges.
• Positioning blocks.

Step 1 - Lateral

• Place the patient in lateral recumbency.
• Rotate the skull until the median sagittal plane is parallel to the film.
• Ensure that the interpupillary line is perpendicular to the film.
• Maintain the position by use of 15 degree foam wedges place under the angle of the mandible and under the nose.
• Sometimes it is helpful to place a pad against the dorsal aspect of the skull, backed by a sandbag. This prevents the skull sliding away from its correct position.
• Center with a vertical beam midway along a line joining the external auditory meatus with the outer edge of the orbit (the orbitomeatal line).
• Collimate to include from the tip of the nose to the caudal edge of the cranium, and from the dorsal edge of the cranium to the ventral mandible, for a full examination .
• Centring and collimation can be varied according to the area of particular interest     .

Step 2 - Dorsoventral

• Place the patient in sternal recumbency.
• Elevate the skull and cassette on blocks.
• Place a long sandbag across the back of the neck. This will help maintain a straight position.
• Ensure that the interpupillary line is horizontal and the median sagittal plane is vertical.
• Center in the midline between the orbits .
• Collimate to include from the tip of the nose to the caudal edge of the cranium, and the skin surfaces laterally, for a full examination.
• Centering and collimation can be varied according to the area of specific interest .
  The endotracheal tube will need to be removed unless the examination is aimed purely at lateral structures. Remember to check positioning following removal of the tube.

Step 3 - Intraoral dorsoventral nasal chambers

• Position the patient in sternal recumbency.
• Raise the head on blocks.
• Ensure that the median sagittal plane is vertical and the interpupillary line is horizontal.
• Place the film in the mouth, on top of the endotracheal tube, one corner leading, as far back as it will go.
• Center with a vertical beam in the midline, half way between the caudal corner of the film and the external nares.
• Collimate to include this area, with the bones of the maxilla included laterally  .

Poor positioning

• Because of the fine structures involved, positioning must be accurate.
• The most common problem is rotation.
• To avoid this the skull must be considered in all its planes. Draw imaginary lines and use fingers and hands to judge when a plane is in its correct position.

Other

• Wrong exposure factors.
• Poor processing.
• Equipment failure.

Refereed papers

• Recent references from PubMed and VetMedResource.
• O'Brien R T, Evans S M, Wortman J A et al (1996) Radiographic findings in cats with intranasal neoplasia or chronic rhinitis - 29 cases (1982-1988). JAVMA 208 (3), 385-389 PubMed.