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 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 focusing 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 cleanly through the disc spaces, with the result that spaces may appear artifactually narrowed.
• In spinal radiography of the cat (as opposed to the dog) it is less likely that the disc space width will be of major interest.
• Generally it is acceptable to include longer expanses of the spine where a less specific survey is needed, but the collimation described is applicable to a detailed examination.
• In judging whether a patient is positioned without rotation it is worth bringing eye level down to patient level. Pinpoint landmarks, (such as sternum and spinous processes), with your fingers and then check that the fingers are in the same plane.
• Accurate centering 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.
• The objective is to produce radiographs showing the area of interest without rotation of the vertebrae or artificial narrowing of the disc 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, with or without dislocation/spondylolisthesis     .
• Discospondylitis  Diskospondylitis.
• Spinal deformities.
• Vertebral neoplasia.
• Spondylosis   (hypervitaminosis A Hypervitaminosis A   ).
• Intervertebral disk prolapse/herniation (myelography often required for this).

Advantages

• Non-invasive although often requires general anesthetic.

Disadvantages

• May require myelography to define the lesion.

Preparation

• Dependent upon method of chemical restraint: whether general anesthetic or sedation.

Procedure

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

Criteria for choosing test

Is the examination appropriate?

• 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?

Choosing the right projections

Lateral

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

Ventrodorsal

• Standard projection.
• Can be omitted in some cases, such as follow-up examinations for discospondylitis or control films for myelography in cases where disc space narrowing or calcification are the main possible findings.

Obliques

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

Risk assessment

Other involvement

• Radiographer / Technician carrying out radiography.

Minimum equipment

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

Ideal equipment

• High output X-ray machine.
• Rare earth screens.
• Automatic processing facilities.
• X-ray table with Potter-Bucky diaphragm.

Minimum consumables

• X-ray film.
• Pharmaceuticals for chemical restraint.

• One to two 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.

Cervical spine

• Two films are necessary to cover the whole cervical spine (irrespective of patient size).
• A grid is not needed for the cranial cervical spine.
• 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 to prevent it dipping towards the film.

Cranial cervical spine

• 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.

Caudal cervical spine

• 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 to 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.

Thoracic spine

• Three 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, achieved usually by padding under the sternum, but 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   .

Cranial thoracic spine

• Center one third to one half way along the length of the scapula. For dorsoventral centering, 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 thoracic spine between the cranial and caudal edges of the scapula.
• Expose on expiration.

Mid thoracic spine

• Center at the level of the caudal border of the scapula.
• Collimate to overlap with the cranial thoracic view and to within a few cm of the last rib.

Thoraco-lumbar junction

• 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 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.

Lumbar spine

• 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 ilium 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.

Mid-lumbar spine

• Center the beam at a level half-way between the last rib and the cranial border of the ilium.
• Centering 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 ilium.
• The dorsal collimation border should be within the skin surface     .
• Expose on expiration.

Lumbo-sacral junction

• To center accurately for this film, palpate the depression in the ilium. The junction between L7 and S1 lies at this level.
• Collimate closely.

Caudal sacral, and coccygeal vertebrae

• 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 the 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.

Cervical spine

• 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.

Cranial cervical spine

• Center with a vertical beam in the midline, midway between the atlas (by palpating the wings) and the cranial border of the scapula.
• Collimate to include the atlanto occipital joint and the first four to five cervical vertebrae.
• Collimate laterally to the edges of the musculature, by palpation.

Caudal cervical spine

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

Thoracic spine

• It can be very difficult to keep the patient from rotating. Take care to use enough immobilization aids, for example between the sides of the thorax and the inside of the trough.
• Three films are needed to cover the entire thoracic spine.

Cranial thoracic spine

• Center the beam in the midline at the level of the sternal notch.
• Collimate to include the area between the cranial edge of the scapula and the midpoint of the sternum, with close collimation laterally.

Mid-thoracic spine

• Center the beam in the midline at the midpoint of the sternum.
• Collimate to include the mid section of the thoracic spine, with close collimation laterally.
• Expose on expiration.

Caudal thoracic spine (thoracolumbar junction)

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

Lumbar spine

• 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 higher exposure than the thoracic, this is often not the case in the ventrodorsal.
• Ensure that the thorax is unrotated.
• "Frogleg" the hindlimbs for maximum stability and immobilize.

Mid-lumbar spine

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

Lumbosacral junction

• 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.

Coccygeal vertebrae

• 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.
• Poor processing.
• Equipment failure.

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.