Spine: butterfly vertebrae

• Cause: abnormal vertebral development mostly seen in brachycephalic, screw-tailed breeds.
• Signs: rarely clinically significant, incidental finding on survey radiograph. However, clinical myelopathies associated with butterfly vertebrae are generally traumatic or compressive and occur as a result of malformation or instability of the vertebral column. They are often treatable.
• Diagnosis: radiography.

• Usually asymptomatic - incidental finding on radiograph.

• May be recognized at any age in asymptomatic form.

• Bulldog Bulldog.
• Pekingese Pekingese.
• Pug Pug.
• Boston Terrier Boston Terrier.

• Low to moderate cost incurred in diagnostic work-up, eg costs increase if myelography is required to demonstrate cord compression.

• Decubital ulcers, urine scald in recumbent animals as a result of spinal instability/spinal cord compression.

• No known specific cause but associated with screw-tailed breeds, therefore may be genetically transmitted.

• Presently unknown.

Specific

• Presently unknown.

• Malformation originating in the embryonic period of development.
• Butterfly vertebra is a vertebral body/intervertebral disk abnormality which is mesodermal in origin.
• Result from incomplete intradiskal migration of notochordal material resulting in bificentrum formation.
• Persistence of the embryonic notochord, or its sagittal cleavage, may produce a sagittal cleft of the vertebral body dorso-ventrally.
• The cranial and caudal vertebral end-plates have a funnel shape and in dorso-ventral radiographs, the vertebral body looks like a butterfly.
• The butterfly vertebra is also characterized by lateral spread of its two halves and compensatory growth of the adjacent normal vertebrae to fill in the funnel-shaped depressions.

• Improper embryogenesis → abnormal growth and development → some narrowing of vertebral canal → pressure on cord in area.
• If the vertebral body is very diminutive it may result in kyphotic angulation, especially if associated with centrum hypoplasia.

• When clinical signs occur, onset is typically acute (hours, days).

• Typically involve thoracic vertebrae.
• When signs occur, seen as a thoracolumbar myelopathy:
  • Paresis/paraplegia.
  • Hindlimb hyperreflexia.
  • Incontinence.

• Typically acute onset of signs as a result of traumatic/compressive spinal cord dysfunction.

• When signs occur, most frequently see:
  • Hindlimb paresis/paralysis.
  • Increased spinal reflexes in hindlimbs.
  • Fecal/urinary incontinence.
  • Pain on palpation of spinal column.

• Abnormal shape vertebrae Radiography: spine.
• T7 vertebrae reported as most commonly affected followed by T8 and T12.

• Spinal instability.
• Vertebral malformation.

• Traumatic/compression myelopathy may be characterized by varying degrees of petechial hemorrhages, dilated myelin sheaths, macrophage infiltration, and necrosis of the spinal cord (neuronal degeneration, cavitation).

• Other vertebral anomalies :
  • Block vertebra .
  • Hemivertebra Spine: hemivertebra .
  • Articular facet aplasia/dysplasia.
  • Transitional vertebrae Transitional vertebrae.
  • Spinal stenosis.
• Intervertebral disk disease Intervertebral disk: type 2 herniation (if dog >2 years of age).

• Spinal cord tumors Spinal cord diseases: overview Spine: neoplasia neoplasia.
• Spinal trauma Spine: fracture / luxation Spinal cord: concussion.

• Other developmental anomalies:
  • Arachnoid cyst Spine: arachnoid cyst.
  • Spinal dysplasia.

• Surgical decompression/spinal stabilization if associated with spinal cord compression Spinal surgery: overview.
• High-quality nursing care:
  • Supportive care.
  • Bladder decompression.
  • Prevention of decubital ulcers/urine scald.

• Clinical signs.

Treatment

• Attention to bedding and toilet function in recumbent dogs.

Monitoring

• Ongoing history.
• Clinical signs.

• Good: rarely causes clinical signs.
• Guarded/good: in dogs requiring surgery that are treated early.

• Look for improvement in clinical signs following surgical intervention.

• Incorrect diagnosis.
• Owner non-compliance.
• Inadequate nursing care.
• Spinal trauma not treated early and aggressively.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Gutierrez-Quintana R, Guevar J, Stalin C et al (2014) A proposed radiographic classification scheme for congenital thoracic vertebral malformations in brachycephalic "screw-tailed" dog breeds. Vet Radiol Ultrasound. 55 (6), 585-91 PubMed.
• Westworth D R, Sturges B K (2010) Congenital spinal malformations in small animals. Vet Clin Small Anim 40 (5), 951-981 PubMed.
• Bailey C S & Morgan J P (1992) Congenital spinal malformations. Vet Clin North Am Small Anim Pract 22 (4), 985-1015 PubMed.
• Braund K G, Shores A, Brawner W R Jr. (1990) The etiology, pathology and pathophysiology of acute spinal cord trauma. Vet Med 85 (7), 684-691 VetMedResource.

Other sources of information

• Braund K G (1994)Clinical Syndromes in Veterinary Neurology.2nd edn. St. Louis. Mosby Year Book. pp 280-281.
• Oliver, Hoerlein & Mayhew (1987)Veterinary Neurology.pp 203.
• Bojrab M J (1983)Disease Mechanisms in Small Animal Surgery.2nd edn. Lea & Febiger. pp 954.