Disc Protrusion

Intervertebral disc degeneration (Image sourced from Bristol Biomed Image Archive with permission)

Occurs mainly in dogs
Almost always dorsal protrusion due to eccentric position of nucleus pulposus
Main sites are cervical and lumbar regions
- Thoracic vertebrae have conjugal ligaments
Degeneration precedes protrusion (two patterns):
- Chondroid
  - In chondrodystrophic breeds
  - Concurrent calcification of degenerated nucleus pulposus
  - Progressive loosening and fragmentation of overlying annulus fibrosis fibres
    - Damaged by both compressive and rotational forces
  - Predisposing degeneration of the discs occurs by one year of age in most of the dogs
  - Protrusion usually occurs in males, 3-6 years of age
  - Sudden complete protrusion -> severe damage to spinal cord in the area
  - Widespread necrosis and haemorrhage
  - Extruded material is gritty, hemorrhagic or “cheesy”
- Fibroid
  - In non-chondrodystrophic breeds, horses, pigs
  - Usually occurs later in life
  - Pathogenesis:
    - Progressive dehydration and collagenisation of nucleus pulposus
    - Fraying and fragmentation of lamellar annulus fibrosis fibres
    - -> Attempts to repair by fibrosis
    - -> Weak area in the annulus
    - -> Partial protrusion (rarely may calcify) of nucleus into spinal canal
      - May be dorsal or lateral
    - -> Pressure on spinal cord
    - -> Demyelination of white matter
    - -> Progressive weakness of structures innervated distally to the lesion
  - Disk material may enter blood vessels causing fibrocartilagenous embolism
    - May present without any disk symptoms

Sudden protrusion can occur in any breed due to traumatic compression of spinal cord