Small Animal Spinal Radiography Series: Cervical Spine Radiography

Imaging Essentials provides comprehensive information on small animal radiography techniques. This article is the first in a 3-part series covering cervical, thoracic, and lumbar spine radiography.

The following anatomic areas have been addressed in previous columns; these articles are available at todaysveterinarypractice.com (search “Imaging Essentials”).

• Thorax
• Scapula, shoulder, and humerus
• Abdomen
• Elbow and antebrachium
• Pelvis
• Carpus and manus
• Stifle joint and crus
• Tarsus and pes

Spinal radiographs are indicated for:

• Evaluation of traumatic injuries
• Neck and back pain
• Pain or neurologic issues associated with thoracic or pelvic limb lameness isolated to these regions.

Each radiographic projection is a separate study and should be radiographed as such. High quality, correctly positioned and collimated radiographs are required in order to provide an accurate assessment of the area of interest, especially for surgical planning.

ROUTINE VIEWS

Lateral and ventrodorsal views are considered the minimum orthogonal radiographs for the spine. Due to the angled, divergent nature of the x-ray beam, the area of the spine in the center of the field of collimation will be the area that provides the correct anatomic detail and intervertebral disk space widths.

If there is a suspected abnormality at the edge of the image, a repeat collimated image centered at the area of interest is required for complete evaluation. Recollimated images are important because they depict common areas of disease (ie, intervertebral disk spaces) that are typically at the edge of the film/image, which could be misinterpreted as narrowed due to the divergent nature of the x-ray beam.

A routine cervical spine study includes:

1. Open lateral image of entire cervical spine
2. Open ventrodorsal image of entire cervical spine
3. Collimated image of lateral cervicothoracic spine
4. Collimated image of ventrodorsal cervicothoracic spine.

Lateral Projection: Cervical Spine

For the lateral projection, position the patient in lateral recumbency (Figure 1).

• Tape the thoracic limbs together evenly and pull caudally.
• Tape or sandbag the thoracic limbs in this caudal position, which places the humerus and glenohumeral joint below the cervical spine, eliminating superimposition. There will always be some degree of superimposition of the scapula.
• Move the lumbar area of the dog dorsally, allowing the cervical spine to align with the horizontal collimation light.
• Place the skull in lateral position; then extend the skull and spine naturally and pull them straight cranially.

If the patient is a large-breed dog, place a sponge under the cervical spine and skull cranial to the shoulder. The sponge elevates the cranial portion of the cervical spine, making it level and lateral with the caudal portion of the cervical spine.

Collimated Projection: Cervicothoracic Spine

The collimated lateral image is centered over the cervicothoracic spine, and extends from the mid cervical spine (cranial limit of field of view [FOV]) to just caudal to the scapulohumeral joint.

Lateral Collimation

For the lateral projection, the FOV excludes the ventral and dorsal soft tissues of the neck, only including the cervical vertebral bodies and immediate soft tissues adjacent to the spine.

For all patients:

• Palpate the vertebrae of the cervical spine and place the horizontal line of the FOV at this plane.
• For smaller patients, collimate the FOV to include the caudal portion of the skull (cranial limit) to just caudal of the scapulohumeral joint (caudal limit).
• For larger patients (cranial and caudal images):
  • The cranial projection FOV should include the caudal portion of the skull to just cranial to the level of the scapulohumeral joint.
  • The caudal projection FOV is centered just dorsal to the humeral scapular joint and first rib; it should extend cranially to the mid cervical spine and caudally to approximately the third rib.

The radiographic marker is placed along the dorsal and cranial aspect of the collimated FOV.

Ventrodorsal Projection: Cervical Spine

Position the patient in dorsal recumbency (Figure 2).

• If a positioning trough is used, place the entire cervical spine within the trough to eliminate any edge artifacts associated with the imaging tray.
• Extend the skull and neck and align them with the manubrium.
• Pull the thoracic limbs caudally and either tape together or individually.

Collimated Projection: Cervicothoracic Spine

The caudal ventrodorsal projection used for large-breed dogs (see Ventrodorsal Collimation) also serves as the collimated cervicothoracic image for all dogs and cats.

Ventrodorsal Collimation

For the ventrodorsal projection, the FOV excludes the lateral soft tissues of the neck, only including the central cervical vertebral bodies and immediate soft tissues adjacent to the vertebral column.

For all patients:

• Palpate the vertebrae of the cervical spine and place the horizontal line of the FOV at this plane.
• For smaller patients, collimate the FOV to include the caudal portion of the skull and caudal to approximately the third rib.
• For larger patients (cranial and caudal images):
  • The cranial projection FOV should include the caudal portion of the skull to just cranial to the manubrium.
  • The caudal projection FOV should extend to mid cervical spine cranially and extend caudally to approximately the third rib. If allowable, the tube head should be angled approximately 10° toward the dog or cat’s head, which aligns the angle of the x-ray beam with the angle of the caudal cervical intervertebral disk spaces, eliminating superimposition of the vertebral body over the intervertebral disk space.

The radiographic marker is placed along the right cranial aspect of the image in the collimated FOV.

ADDITIONAL VIEWS

Lateral Oblique Projection: Cervical Spine

Trauma or congenital malformation may cause atlantoaxial luxation or instability of the joint between cervical vertebra 1 and 2. To visualize the dens, an oblique projection from the lateral position is obtained.

If an atlantoaxial instability is suspected, it is imperative that care be taken not to luxate the vertebra further, resulting in spinal cord trauma. Sedation is highly recommended for these patients to avoid additional movement.

Position the patient in lateral recumbency (Figure 3).

• Tape the forelimbs and pull caudally with gentle pressure.
• Obliquely angle the spine in a ventral direction, which is achieved by placing a sponge under the dorsal skull and shoulder.

For collimation, the FOV is centered at the atlantoaxial joint. The cranial border is at mid skull, while the caudal border includes cervical vertebra 3 and 4.

Lateral Flexed & Extended Projections: Cervical Spine

Flexed and extended projections are used for cervical vertebral malformation (CVM) or Wobbler’s syndrome.

Compression of the spinal cord due to abnormalities occurs mainly in large-breed dogs and affects the caudal cervical vertebrae and their articulations, resulting in paraparesis, tetraparesis, or ataxia. The large-breed dog will need a cranial and caudal projection as with a naturally positioned cervical spine projection.

For both projections, position the patient in lateral recumbency, with the forelimbs taped and pulled caudally.

For the extended projection (Figure 4), push the skull and cervical spine dorsally.

• Ensure that the caudal cervical vertebra are angled dorsally, not merely pivoted at the mid cervical spine.
• Hold the skull in place with a sandbag or tape.

For the flexed projection (Figure 5), pull the skull and cervical spine ventrally toward the forelimbs.

• Ensure that the cervical spine is flexed at the level of the caudal cervical vertebra and not merely arched at the mid cervical spine.
• Hold the skull in place with a sandbag or tape.

For collimation, due to the flexion and extension of the cervical spine, the FOV includes most of the soft tissues of the neck.

Ventrodorsal Oblique Projection: Cervical Spine

Subtle lesions, fractures, and intervertebral disk disease are a few of the conditions that may require a ventrodorsal oblique projection of the spine.

From the straight ventrodorsal position of the cervical spine, obliquely rotate the patient to the left approximately 10° to 15°; then take the radiograph. Then rotate the patient to the right approximately 10° to 15° and take another radiograph.

Set the collimation of the oblique ventrodorsal projections as described for the ventrodorsal projection of the cervical spine.

QUALITY CONTROL

To make certain the desired technique has been achieved, use the following guidelines to determine whether the appropriate anatomy is included in the images.

For both lateral and ventrodorsal projections of the cervical spine:

• The cranial border should include the caudal aspect of the skull.
• The caudal border should, at least, include T1.

For the lateral projection of the cervical spine:

• The wings of the Atlas (C1) should be even and superimposed.
• Each cervical vertebral body should be even with the superimposed transverse processes.
• On a straight cervical spine, the wings of C1 will overlap each other and be superimposed over the dens, which is not visualized.

For the ventrodorsal projection of the cervical spine:

• The spinous processes should be superimposed over the vertebral bodies.
• The spinous process over the Axis (C2) should resemble a thin line bisecting the vertebral body.