ISSN 2398-2969      

Intervertebral disk: type 1 herniation

icanis

Synonym(s): Hansen type 1 disk disease, Disk extrusion, Disk rupture


Introduction

  • Intervertebral disk disease (IVD) can occur in any area of the spinal cord caudal to C1-2.
  • Cause: chondroid metaplasia (degeneration) of nucleus pulposus characterized by loss of glycosaminoglycans and decrease in water content → loss of shock absorbency → nuclear material extrudes through all layers of the ruptured dorsal annulus fibrosus into the vertebral canal causing spinal cord compression. Often seen in chondrodystrophic breeds.
  • Signs: acute onset non-traumatic spinal cord pathology, pain → lack of deep pain sensation.
  • Diagnosis: neurological examination, radiography/myelography, advanced imaging.
  • Treatment: conservative (cage rest) or surgical decompression.
  • Prognosis: guarded if severe.
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Pathogenesis

Etiology

  • Chondroid metaplasia of the nucleus pulposus.

Predisposing factors

General
  • Chondrodystrophic breeds.

Pathophysiology

  • Type I intervertebral disk abnormality is seen in chondrodystrophic breeds of dogs which have chondroid metaplasia of the nucleus pulposus beginning early in life (usually first 2 years of life - can begin as early as 2 months of age).
  • This metaplasia is characterized by a loss of glycosaminoglycans, an increase in collagen content, and a decrease in water content, resulting in loss of the hydroelastic properties of the disk and its ability to withstand pressure.
  • Chondroid metaplasia occurs along the entire vertebral column.
  • Intervertebral disk extrusion is typically associated with chondroid degeneration and involves the herniation of nuclear material through all layers of the ruptured annulus fibrosus into the vertebral canal.
  • The abnormal forces generated by the degenerate and mineralised nucleus pulposus cause tears to develop within the annulus fibrosus through which the disk extrude.
  • The extrusion causes dorsal, dorsolateral or circumferential compression of the spinal cord.
  • Acute disk extrusion is characterized by extradural hemorrhage and soft disk material.
  • Thoracolumbar area accounts for most cases causing upper motor neuron lesions in the pelvic limbs.
  • 75-100% of chondrodystrophic puppies → disk degeneration to chondroid tissue → mineralized (90% by 2 years old).
  • Disk designed to dissipate concussive forces centrifugally.
  • Disk degeneration or excessive force → dorsal displacement of material and rupture of dorsal annulus → nucleus forced dorsally through the relatively thin dorsal annulus into vertebral canal → damaged cord parenchyma.
  • Extrusion of disk material causes primary spinal cord injury and associated neurological signs by concussion Spinal cord: concussion , compression, laceration and ischemic events.
  • Force of impact on the cord rather than the size is critical: small, high velocity explosive extrusion is far more damaging to the cord parenchyma than a less forceful impact from a larger, slower fragment.
  • Severe swelling and inflammation of the cord following impact → edema and autolysis → cord destruction propagates along the cord, ie ascending myelomalacia Diffuse progressive myelomalacia.
  • Autolytic processes may → hemorrhage, myelomalacia → euthanasia.

Timecourse

  • Acute onset with deterioration within hours - several days.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hillman R B, Kengeri S S, Waters D J (2009) Reevaluation of predictive factors for complete recovery in dogs with nonambulatory tetraparesis secondary to cervical disk herniation. JAAHA 45 (4), 155-163 PubMed.
  • Forterre F, Konar M, Spreng D (2008) Influence of intervertebral disk fenestration at the herniation site in association with hemilaminectomy on recurrence in chondrodystrophic dogs with thoracolumbar disc disease: A prospective MRI study. Vet Surg 37 (4), 399-405 PubMed.
  • Levine J M, Levine G J, Johnson S I, Kerwin S C, Hettlich B F, Fosgate G T (2007) Evaluation of the success of medical management for presumptive cervical intervertebral disk herniation in dogs. Vet Surg 36 (5), 492-499 PubMed.
  • Levine J M, Levine G J, Johnson S I, Kerwin S C, Hettlich B F, Fosgate G T (2007) Evaluation of the success of medical management for presumptive thoracolumbar intervertebral disk herniation in dogs. Vet Surg 36 (5), 482-491 PubMed.
  • Platt S R, McConnell J F, Bestbier M (2006) Magnetic resonance imaging characteristics of ascending hemorrhagic myelomalacia in a dog. Vet Rad & Ultrasound 47 (1), 78-82 PubMed.
  • Ito D, Matsunaga S, Jeffrey N D et al (2005) Prognostic value of magnetic resonance imaging in dogs with paraplegia caused by thoracolumbar intervertebral disk extrusion: 77 cases (2000-2003). JAVMA 227 (9), 1454-1460 PubMed.
  • Brisson B A, Moffatt S L, Swayne S L, Parent J M (2004) Recurrence of thoracolumbar intervertebral disk extrusion in chondrodystrophic dogs after surgical decompression with or without prophylactic fenestration: 265 cases (1995-1999). JAVMA 224 (11), 1808-1814 PubMed.
  • Hay C W & Muir P (2000) Tearing of the dura mater in three dogs. Vet Rec 146 (10), 279-282 PubMed.
  • McKee M (2000) Intervertebral disk disease in the dog: 2. Management options. In Practice 22 (8), 458-471 VetMedResource.
  • Olby N J, Munana K R, Sharp N J H & Thrall D E (2000) The computed tomographic appearance of acute thoracolumbar intervertebral disc herniations in dogs. Vet Rad Ultra 41 (5), 396-402 PubMed.
  • Dhupa S, Glickman N W & Waters D J (1999) Functional outcome in dogs after surgical treatment of caudal lumar intervertebral disk herniation. JAAHA 35 (4), 323-331 PubMed.
  • Otani K et al (1997) Experimental disk herniation - evaluation of the natural course. Spine 22 (24), 2894-2899 PubMed.
  • Takahiashi T et al (1997) Treatment of canine intervertebral disk displacement with chondroitinase ABC. Spine 22 (13), 1446-1447 PubMed.
  • Seim H B III (1996) Conditions of the thoracolumbar spine. Semin Vet Med Surg (Small Anim) 11 (4), 235-253 PubMed.
  • Bracken M B, Shepard M J, Collins W F et al (1990) A randomized, controlled trial of methylprednisolone or naloxone in the treatment of acute spinal cord injury. New Engl J Med 322 (20), 1405-11 PubMed.
  • Hoerlein B F (1979) Comparative disk disease - Man and dog. JAAHA 15 (5), 535-45 VetMedResource.
  • Hansen H J (1951) A pathologic anatomical interpretation of disk degeneration in dogs. Acta Orthop Scand 20 (4), 280-93 PubMed.

Other sources of information

  • Bartels J E (1994)Intervertebral disk disease.In:Textbook of Veterinary Diagnostic Radiology.2nd edn. Ed: Thrall D E. Philadelphia:W B Saunders. pp 59.
  • Oliver, Hoerlein & Mayhew (1987)Veterinary Neurology.Saunders. pp 321-341.
  • Bojrab M JDisease Mechanisms in Small Animal Surgery.2nd edn. Lea & Febiger. pp 960-970.

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