Contributors: Fraser McConnell

 Species: Canine   |   Classification: Miscellaneous

Introduction

Overview

Radiographic considerations

  • A low kV, high mAs technique will maximize contrast.
  • Detail screens and film should be used for small dogs.
  • A grid will be required for medium to large breeds.
  • Survey radiography is relatively insensitive for the diagnosis of many spinal conditions.
  • Myelography Radiography: myelography Radiology: myelography is required in most cases to confirm site of cord compression or disease.
  • At least 2 orthogonal projections need to be taken.
  • Positioning is extremely important as rotation and obliquity of the spine can make interpretation very difficult and may lead to erroneous diagnosis.
  • Due to geometric effects of the diverging primary beam there will be artefactual narrowing of the intervertebral disks at the periphery of the film.
  • For this reason multiple radiographs are required, centered on each region of the spine to avoid erroneous diagnosis of narrowed intervertebral disks.

Restraint

  • Spinal radiography usually requires anesthesia to facilitate positioning.
  • Care needs to be taken moving patient with suspected vertebral fractures or luxations as muscle relaxation with anesthesia may result in fracture/luxation becoming unstable.

Indications

  • Investigation of neurological disease localized to spine.
  • Back or neck pain.
  • Investigation of FUO.
  • Investigation of certain tumors, eg myeloma Myeloma.

Radiographic anatomy

  • The spine is divivided into cervical, thoracic, lumbar, sacral and caudal segments.
  • The number of vertebrae is usually constant and normally divided:
    • 7 cervical Spine normal cervical - radiograph lateral.
    • 13 thoracic Spine normal thoracic - radiograph lateral.
    • 7 lumbar Spine normal lumbosacral - radiograph lateral.
    • 3 sacral Spine normal lumbosacral - radiograph lateral.
    • A variable number of caudal vertebrae.
      Correct localization is vital and complete survey radiographs should not replace a full neurological examination.
  • Neurological examination will help in interpretating a finding of multiple abnormalities.

Growth plate closures

  • The vertebrae (except C2) are formed from 3 ossification centers:
    • 1 for the centrum.
    • 1 for each neural arch.
  • The caudal physes of the vertebral bodies are not ossified at birth but become mineralized between 2 -8 weeks post-natally and are fused by approximately 9 months.
  • The neural arches that form the vertebral pedicles, laminae and dorsal spinous processes are separate at birth.
  • The axis forms from 7 ossification centers, the fusion times of which are variable:
    • Dens unites with body at 7 months.
    • Caudal epiphyses unite at 9 months.
  • Atlas originates from 3 primary ossification centers which unite at 4 months.

Transitional vertebrae

  • These show characteristics of adjacent segments.
  • Most commonly seen in lumbar and thoracic spine.
  • The last thoracic vertebra may develop a transverse process instead of a rib or the first lumbar vertebra may have a rib Spine transitional vertebrae (thoracolumbar) - radiograph VD.
  • The 7th lumbar vertebra may articulate with the sacrum.
  • Transitional vertebrae are often assymetric.
    These usually have no clinical significance but unilateral sacralization of L7 has been postulated to predispose to hip dysplasia Hip: dysplasia and cauda equina syndrome Cauda equina neuritis.

Interpretation

Vertebrae

  • The number, shape, position, margins and opacity of the vertebral borders should be scrutinized.
  • The size, shape and opacity of the intervertebral foramen should be assessed together with the width of the articular facet joint.
  • The width and opacification of the intervertebral disk space should be carefully assessed and compared with adjacent diskspaces.
  • The width of the vertebral foramen at the cranial and caudal ends of each vertebrae should be similar.
  • The opacity of the dorsal spinous processes should be assessed.

Vertebral canal

  • The vertebral canal should be gently curved and smooth.
  • There should be no steps or marked changes in diameter.
  • There is usually widening of the vertebral canal at the cervical intumescence at C6/C7 Spine normal cervical - radiograph lateral and lumbar intumescence at L4/L5 Spine normal lumbosacral - radiograph lateral.

Hemivertebrae

  • Hemivertebrae Spine: hemivertebra are most common in thoracolumbar spine and in screw-tailed breeds.
  • Associated with deviation of the spine Spine hemivertebra (thoracic) - radiograph VD and may result in narrowing of the canal but often incidental Spine hemivertebra (thoracic) - radiograph lateral.
  • May be failure of ossification of either lateral, vertical or dorsal half of the vertebra.

Spina bifida

  • Midline cleft in vertebral and may be absent or reduced size of dorsal spinous process Spina bifida.
  • May be associated with cord defects or incidental finding.

Wedge vertebra

  • Block vertebrae Spine block vertebrae - radiograph lateral result from failure of segmentation of somites and results in apparent fusion.
  • There may or may not be fusion of dorsal spinal processes and dorsal laminae or pedicle.
  • In some cases a vestigial disk space may be seen separating the vertebral bodies.
  • Block vertebrae Spine block vertebrae - radiograph lateral may be normal length or short.
  • Abnormal block vertebrae are of no clinical significance but may lead to excess loading of adjacent vertebrae predisposing to disk degeneration.

Butterfly vertebrae

  • Very common in the severely brachycephalic dogs especially Bulldogs, Pugs, Boston terrier.
  • Butterfly vertebrae Spine: butterfly vertebrae result from cleft through vertebral body in a sagittal plane.
  • Cranial and caudal end plates are funnel shaped.

Appearance

  • Vertebral density may be increased or decreased depending on pathology (neoplasia, metabolic):
  • Evaluate the entire film as other findings may help to narrow the differential diagnosis list, eg:
    • Prostatomegaly may be due to prostate neoplasia or prostatic mass may cause similar signs to lumbar spine disease or may be the cause of diskospondylitis Diskospondylitis.

Pitfalls

  • Breed variations - small dogs have relatively larger spinal cords compared to large dogs. This results in thinner contrast columns following myelography.
  • Congenital - abnormalities in the number of vertebrae are common (47% dogs in one study).
  • It is important to recognize abnormalities in vertebrae number (to ensure accurate localization) if spinal surgery is contemplated.
    Unless the entire spine is radiographed it is not possible to determine if there is an alteration in the total number of vertebrae.
  • The dens forms as a separate center of ossification and should not be mistaken for a fracture in young puppies.
  • Composite shadows may superimpose the appearance of a well-circumscribed focal lucency in the mid-body of C5 and C6 on the lateral projection Spine normal cervical - radiograph lateral.
  • The intervertebral disk space of the thoracic vertebrae up to T10/T11 are narrower than the disk spaces of the lumbar and cervical spine.
  • The dorsal spinous process of the thoracic spine especially cranial vertebrae often have a mottled appearance Spine normal thoracic - radiograph lateral and may be misinterpreted as lytic lesions.

Additional studies

Contrast

MRI