Radiography: spine

• Great care must be taken when handling and positioning a patient with a possible instability of the spine.
  An initial lateral survey film (without undue manipulation of the patient), may be appropriate.
• Higher quality images can be obtained following an initial assessment of the extent of the problem.
• Successful radiography of the spine requires strict attention to the details of positioning.
• In the cervical region, satisfactory positioning is usually not possible without a general anesthetic.
• To achieve accurate positioning it is necessary to consider the whole patient, rather than focussing only on the area of interest.
• It is important to remember to avoid rotation of the spine in the craniocaudal direction, as well as the ventrodorsal direction.
• Radiography of a large number of vertebrae on one film is to be avoided, as the oblique rays towards the periphery of the beam will not pass through the disk spaces, with the result that spaces may appear artefactually narrowed.
• In judging whether a patient is positioned without rotation it is worth bringing eye level down to patient level. Pinpoint landmarks, such as sternum/spinous processes, with your fingers and then check that the fingers are in the same plane.
• Accurate centring and collimation in the spine depends more on experience than radiography of most other areas of the body. With practice, it becomes possible to pinpoint features which do not benefit from easily palpable localizing landmarks.
• Liberal use of foam pads is helpful.
  A secondary radiation grid should be used for patients >10 cm in thickness.
• The objective is to produce radiographs showing the area of interest without rotation of the vertebrae or artificial narrowing of the disk spaces.
• The film must be correctly exposed and processed and show the anatomical marker, the patient's identification, the date, and the name of the hospital or practice.

• → Fractures Spine: fracture / luxation , with or without dislocation.
• → Discospondylitis Diskospondylitis .
• → Spinal deformities Spine: butterfly vertebrae.
• → Vertebral neoplasia.
• → Spondylosis  /degenerative disease.
• → Intervertebral disk prolapse/herniation Intervertebral disk: type 2 herniation  , (myelography required to confirm spinal cord compression).
• → Metabolic bone disease.

Advantages

• Non-invasive although may require GA.

Disadvantages

• Often requires myelography to define a soft tissue lesion and confirm spinal cord compression.

• Magnetic Resonance Imaging (MRI) - more expensive but allows visualization of spinal cord, other soft tissues and bone.

Preparation

• Dependent upon method of chemical restraint - whether GA or sedation.

Procedure

• Depends whether imaging whole spine or only one part.
• For latter about 10 min including processing in automatic processor but not including anesthesia or sedation.

Criteria for choosing test

• Can you make the diagnosis without it?
• Can it tell you what you need to know?
• Will your management be affected by the radiological findings?

• Standard projection.
• Shows comparative width of adjacent disk spaces, will detect some fractures, shows alignment of vertebrae, etc.

• Standard projection.
• Necessary for complete evaluation.

• These are sometimes necessary in fracture cases and are useful during myelography to pinpoint more exactly the position of spinal cord or nerve root compression.

Risk assessment

Other involvement

• Radiographer or Veterinary Nurse/Technician carrying out radiography.

Minimum equipment

• X-ray machine.
• Cassettes with high resolution to fast screens, depending on size of patient.
• Secondary radiation grid for larger patients (>10 cm thickness).
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges.
• Protective clothing (lead rubber aprons).
• Positioning trough.
• Film labeling equipment.

Ideal equipment

• High output X-ray machine.
• Rare Earth high resolution screens.
• Automatic processing facilities.
• Film ID camera.
• Grid for patients >10 cm thickness.

Minimum consumables

• X-ray film.
• Pharmaceuticals for chemical restraint/general anesthesia.

• 1-2 competent people.
• Sandbags.
• Foam wedges.
• Positioning trough.

Step 1 - Lateral

• Position the patient in lateral recumbency. The side chosen is not critical.
  If you cannot achieve a well-positioned image after multiple attempts, try repositioning the patient on the other side.

• Collimate to include from the base of the skull through the scapulohumeral joints.
• Two films are necessary to cover the whole cervical spine in patients with large pectoral muscle mass.
• Draw the forelimbs caudally and secure.
• The skull must be in a true lateral position, the median sagittal plane parallel to the film.
• The thorax must also be in a true lateral position.
• A small radiolucent pad is usually required under the middle of the cervical spine in order to prevent it dipping towards the film .

• Palpate the wings of C1 (the atlas), and center with a vertical beam mid-way between this and the cranial border of the scapula.
• Collimate to include the caudal part of the skull and the first five cervical vertebrae.
• For dorsoventral collimation, the musculature around the spine can be palpated and included.

• Center with a vertical beam at the level of the cranial edge of the scapula.
• Collimate to overlap with the film of the cranial cervical spine, that is to include approximately C4 - T3.
  Remember that the cervical spine has a "slope" in relation to the shape of the animal. The caudal part (around the level of the cranial scapula), is about halfway between the dorsal and ventral skin surfaces. Once into the thoracic region, the spine starts to slope dorsally.

• Two films are necessary to cover the whole of the thoracic spine.
• The forelimbs are drawn cranially and secured.
• The thorax must be in a true lateral position, usually achieved by padding under the sternum. However, this is not always the case and it is important to palpate the sternum and the spinous processes and check that they are in the same plane .

• Center of the caudal border of the scapula. For dorsoventral centring, take into account that the spinous processes are long in this region, and that the vertebral bodies therefore lie relatively deep to the dorsal skin surface.
• Collimate to include the cranial and middle (from the first to the 10th or 11th intercostal space).
• Expose on expiration.

• You may need to add padding under the mid lumbar spine. Make sure that the lumbar region is not rotated.
• Center at the level where the last rib meets the spine.
• Craniocaudal collimation should include at least the last three to four thoracic and the first three lumbar vertebrae .
  Do not collimate too tightly in the dorsoventral direction as the kyphosis is fairly marked in this area. The spinous processes are very short at the thoraco-lumbar junction and the vertebral bodies consequently lie quite superficially.
• Expose on expiration.

• Including a thoraco-lumbar view, three films are required to cover the lumbar spine.
• Ensure that both the thorax and the abdomen are unrotated by checking the padding ventrally and dorsally as necessary.
• Most commonly, it is necessary to pad under the lower femur to bring the pelvis lateral.
• Palpate the tubercles on the dorsal ileum to check that they are superimposed and that the pelvis is therefore lateral.
• Run a finger along the lumbar spinous processes to check that the spine is horizontal here and adjust as necessary with padding under the mid-lumbar region.

• Center the beam at a level half-way between the last rib and the cranial border of the ileum.
• Centring in the dorsoventral direction can be judged here by palpation of the transverse processes.
• Craniocaudal collimation should include the vertebrae between the last rib and the cranial border of the ileum.
• The dorsal collimation border should be within the skin surface .
• Expose on expiration.

• To center accurately for this film, palpate the depression in the ileum. The junction between L7 and S1 lies at this level, no matter what size the dog .
• Collimate closely.

• Follow the same principles as in the rest of the spine.

Step 2 - Ventrodorsal

• Position the patient in dorsal recumbency with the trough strategically placed depending on the part of the spine to be examined.
  Remember that fiberglass troughs have edges which are not radiolucent.
• Do not just consider the area of interest when making sure that the patient is unrotated. For example, for radiography of the thoracic spine, make sure that the neck and the abdomen are unrotated as well as the thorax, as the weight of the adjacent area will pull the patient round.

• The endotracheal tube will need to be removed prior to exposure.
• Ensure that the skull and the thorax, as well as the neck, are in a true ventrodorsal position.
• Extend the neck as much as possible.
• Draw the forelimbs caudally and secure.
• Place a pad under the endotracheal tube to prevent it becoming kinked during positioning (remove prior to exposure).
• Two views are needed when the caudal cervical region is much thicker than the cranial cervical region (in large dogs).

• Center with a vertical beam in the midline, midway between the atlas (by palpating the wings) and the cranial border of the scapula.
• The beam may need to be angled to direct the X-rays perpendicular to the spine in order to penetrate the intervertebral disk spaces.
• Collimate to include the atlanto-occipital joint and the first 4-5 cervical vertebrae.
• Collimate laterally to the edges of the musculature by palpation .

• Center with a vertical beam in the midline at the level of the cranial edges of the scapulae.
• Collimate to include C4-T3.

• In narrow-chested dogs it can be very difficult to keep the patient from rotating. Take care to use enough immobilization aids, eg between the sides of the thorax and the inside of the trough.
• The increase in exposure required from lateral to ventrodorsal in a deep-chested dog is considerable. Ensure that you have a clear idea of how much greater the thickness actually is.
• In larger dogs, two films are needed to cover the entire thoracic spine .

• Center the beam in the midline just caudal to midsternum.
• Collimate to include the area from the manubrium to the 10th or 11th intercostal space.
• When collimating laterally, take into account (particularly with a deep-chested dog), that the beam will diverge considerably between the ventral skin surface and the spine itself.
• Collimate tightly.

• Center the beam at the xiphisternum.
• Collimate to include T8-L2.
• Expose on expiration.
  The image densities in this area are likely to vary considerably across the field along with the varying thickness of the patient. The effect of this can be diminished by using a higher kVp/lower mAs technique, up to the point where loss of contrast becomes unacceptable.

• Three films are needed to cover the area: thoracolumbar junction, mid-lumbar, lumbosacral junction.
  While in the lateral projection, the lumbar spine generally requires a substantially higher exposure than the thoracic. This is not often the case in the ventrodorsal.
• Ensure that the thorax is unrotated.
• "Frogleg" the hindlimbs for maximum stability and immobilize.

• Center the beam in the midline at a level halfway between the last rib and the iliac crest.
• Collimate to include L2-L6.
• Expose on inspiration.

• Center the beam in the midline at a level slightly caudal to the iliac crest.
• Collimate to include L6 to caudal sacrum .
• Expose on expiration.

• Follow general principles.
• Use adhesive tape as an immobilization aid if necessary.

• The most common problems in radiography of the spine are in achieving unrotated projections. It is essential to pay careful attention to accurate positioning and not to skimp on padding.
• General anesthesia or heavy sedation is usually necessary for accurate radiographic evaluation.
  Narrowing of disk spaces may be an artifact if evident at the periphery of the film, or on films of awake or rotated patients
• Poor processing.
• Failure to label film.
• Equipment failure.
• Incomplete study.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Galloway A M, Curtis N C, Sommerlad S F et al (1999) Correlative imaging findings in seven dogs and one cat with spinal arachnoid cysts. Vet Radiol Ultrasound 40 (5), 445-452 PubMed.
• Morgan J P (1999) Transitional lumbosacral vertebral anomaly in the dog - a radiographic study. JSAP 40 (4), 167-176 PubMed.
• Penderis J, Sullivan M, Schwarz T et al (1990) Subdural injection of contrast medium as a complication of myelography. JSAP 40 (4), 173-176 PubMed.