Contributors: Justin Goggin, Patsy Whelehan
Species: Canine | Classification: Techniques
- Radiography of the skull requires general anesthesia. This is the only way to obtain accurate projections.
- A grid is necessary when patient thickness >10 cm.
- The different skull shapes are treated similarly for the basic projections.
- Specialised projections such as tympanic bullae require adaptation of technique based on the shape of the skull.
- 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 artefact.
- The anatomical marker, the patient's identification, the date, and the name of the hospital or practice should be clearly shown.
- → Fracture .
- → Bony neoplasia .
- → Soft tissue neoplasia Nasal cavity: neoplasia , eg nasal tumors .
- → Temporomandibular joint disease Temporomandibular joint: disease - overview .
- → Hydrocephalus Hydrocephalus .
- → Nasal foreign body .
- → Ear disease and tympanic bulla involvement Otitis media .
- → Infectious rhinitis Rhinitis.
- 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.
- Magnetic Resonance Imaging (MRI) is the modality of choice for most brain imaging.
- CT is available for brain imaging but artifacts from dense skull bone can obscure lesions, and soft tissue contrast with CT is inferior to MRI.
- Ultrasonography can be used to image the brain if fontanelles present.
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?
- 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, not withstanding the fact that the two sides are overlying each other.
- May show neoplasms involving the bone.
- Standard projection.
- May give information on skull vault shape.
May give misinformation or incomplete information on nasal cavity disease because of overlap of mandible and tongue.
- May show gross fractures, depending on their position.
- Good for fractures of the zygomatic arches.
- Good for productive and destructive bone lesions.
- Good for some mandibular fractures and dislocation of the temporomandibular joints.
- Of some use for tympanic bullae and ear canal disease.
- 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.
- 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.
- There is a problem in obtaining the non-screen (direct exposure) film necessary for this technique.
- Rostrocaudal frontal sinus view allows detection of frontal sinus fluid, masses, bone production or bone lysis.
- Radiographer, or Veterinary Nurse/Technician to carry out radiography.
- X-ray machine.
- Cassettes with high detail screens.
- Processing facilities.
- Immobilization and positioning aids: sandbags, foam wedges, blocks.
- Protective clothing, eg lead-rubber aprons, although patient must be under general anesthesia for complete study.
- For the intraoral nasal view, non screen (direct exposure) film is required. Radiation therapy localization film is optimal for this use (individually wrapped).
Dental occlusal film is suitable for small breed dogs.
- Flexible screens and casetttes are also available which are useful for this technique as they can be positioned within the oral cavity of an anesthetized patient.
If not available, a suitable film can be cut to size and inserted into light-tight envelopes.
- Film labelling system.
- High output X-ray machine.
- Rare earth high detail screens.
- Automatic processing facilities.
- X-ray film.
- Pharmaceuticals for anesthesia.
- One to two competent people.
- Foam wedges.
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° foam wedges placed 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.
- Centering and collimation can be varied according to the area of particular interest .
Step 2 - Dorsoventral
- Place the dog 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 should ideally be removed unless the examination is aimed purely at lateral structures. Remember to check positioning following removal of the tube.
Step 3 - Intra-oral 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 .
Step 4 - Rostrocaudal frontal sinus view
- Position patient in dorsal recumbency with the thoracic region in a "V" trough.
- Orient the skull so that the nose points toward the X-ray tube and the hard palate is perpendicular to the table (stabilize with tape).
- Place a film under the base of the skull.
- Collimate to include the nose, maxillary region and frontal sinuses.
- Make sure exposure setting is based on a measurement from the orbit to the occipital region.
Reasons for Treatment Failure
- 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.
- Inadequate number of views.
- Wrong exposure factors.
- Poor processing.
- Equipment failure.
- Failure to label film.