Acute non-compressive nucleus pulposus extrusion

Acute non-compressive nucleus pulposus extrusion (ANNPE) is a relatively common form of spinal cord injury in dogs and less commonly cats. Other terms used to describe the same condition include traumatic disc extrusion, Hansen Type III disc disease, traumatic disc prolapse, and high-velocity low-volume disk extrusion. The term Type III disc disease is not recommended because Hansen only described two forms of degenerative disc disease and Funquist, who originally reported the features of ANNPE, described it as a subtype of Hansen Type I disc disease.

ANNPE occurs most often during intense exercise or with external trauma when the vertebral column and discs are placed under greater than normal stress leading to a tear in the annulus fibrosus. This allows a small volume of normally-hydrated nucleus pulposus to extrude out of the disc at high velocity leading to spinal cord contusion. Since the extruded material in ANNPE is very hydrated, it either dissipates or is rapidly reabsorbed so there is usually no residual spinal cord compression. However, extradural hemorrhage secondary to laceration of the internal vertebral venous plexus may result in spinal cord compression.

Signalment

ANNPE is most common in older (mean age, 7 years) large and giant breed dogs but can occur at any age and in any breed of dog. Border Collies appear especially prone to the condition.

Clinical signs

Patients with ANNPE experience a peracute onset of clinical signs as the result of external trauma (40%) or during intense exercise (60%). Approximately 60% of dogs vocalize at the time of injury, concurrent with a variable degree of paresis to paralysis. Clinical signs may progress for the first 24 hours but are nonprogressive after that time.

Neurological & physical exam

Neurologic exam findings reflect lesion location. See neurolocalization for additional information. Approximately 90% of affected patients have lateralized clinical signs and about half show spinal hyperesthesia during the initial neurologic exam, but the pain should resolve by 24 hours.

Diagnosis

MR images obtained from a dog with a T12-13 ANNPE after falling while running. Note the classic T2-weighted hyperintense intramedullary lesion (left panels) that is isointense on T1-weighted images (middle panels) and does not contrast enhance (right panels). The nucleus pulposus of the T12-13 disc is smaller than adjacent discs. Mild extradural contrast enhancement is noted (bottom right), along with enhancement of epaxial muscle (upper right) presumably secondary to trauma.

MRI is the imaging modality of choice. The classic finding is focal, often lateralized, intramedullary T2-weighted hyperintense signal over an intervertebral disc space. The lesion is usually well-demarcated, frequently affecting the gray matter. This intramedullary signal is thought to be spinal cord edema secondary to contusive spinal cord injury. Mild contrast enhancement of the intramedullary lesion or the meninges/epidural space is sometimes present. The affected disc often has a visibly smaller volume of nucleus pulposus on T2-weighted images compared to nearby normal discs and the disc space may be mildly narrowed. A small volume of extradural material is sometimes visible, which may be due to small volume disc material or hemorrhage from the ventral internal vertebral venous plexus that is occasionally lacerated during extrusion of the nucleus pulposus.

If MRI is unavailable, CT or myelogram can be performed, but neither imaging modality will reveal the intramedullary lesion. They can, however, exclude other common causes of spinal cord dysfunction with similar history and clinical signs, such as Type I intervertebral disc disease and vertebral fracture/luxation. A presumptive diagnosis of ANNPE (or fibrocartilaginous embolism) may be achieved with compatible history/clinical signs and normal CT / myelogram.

Treatment

Medical management is usually recommended for affected patients. ANNPE is almost always a nonsurgical condition, except in uncommon to rare cases in which there is spinal cord compression from laceration of the ventral internal vertebral venous plexus during the traumatic event. To date, no medications, including corticosteroids, have been shown to improve the degree of recovery or to shorten the duration of clinical signs. Analgesics may be needed initially in patients with spinal hyperesthesia. Modified activity with short leash walks just long enough to eliminate and no running, jumping, or use of stairs is recommended for 4-6 weeks to reduce the risk of additional extrusion. Nursing and bladder care are important, including manual expression or urinary catheterization as needed, thick bedding with frequent turning to prevent pressure sores and decubital ulcers, and keeping the patient clean and dry to prevent urine scald. Professional and at-home physical rehabilitation is important to help improve strength and coordination, improve joint range of motion, and reduce muscle atrophy.

Prognosis

The prognosis is good. Limited published studies to date have reported recovery rates of 66.7% to 100%. Negative prognostic indicators include severity of clinical signs, failure to improve within two weeks, urinary or fecal incontinence, absent nociception, and large and giant breed dogs (presumably due to the difficulty of nursing care for these patients). One study (DeRisio, 2009) found that patients with a cross-sectional area of the intramedullary lesion > 90% diameter of the spinal cord were more likely to have a negative outcome (sensitivity 86%, specificity 96%). Recovery times vary widely in published studies, but dogs that recover usually do so within days to weeks, sometimes up to 2-3 months.
 

Further reading

  • Chang Y, Dennis R, Platt SR, et al. Magnetic resonance imaging of traumatic intervertebral disc extrusion in dogs. Vet Rec 2007;160:795–9.
  • Chow K, Beatty JA, Voss K, et al. Probable lumbar acute non-compressive nucleus pulposus extrusion in a cat with acute onset paraparesis. J Feline Med Surg 2012;14:764–7.
  • De Decker S, Fenn J. Acute herniation of nondegenerate nucleus pulposus: Acute noncompressive nucleus pulposus extrusion and compressive hydrated nucleus pulposus extrusion. Vet Clin No Amer Small Anim Pract 2018;48:95-109.
  • De Risio L. A review of fibrocartilaginous embolic myelopathy and different types of peracute non-compressive intervertebral disk extrusions in dogs and cats. Front Vet Sci 2015;18:24.
  • De Risio L, Adams V, Dennis R, et al. Association of clinical and magnetic resonance imaging findings with outcome in dogs with presumptive acute noncompressive nucleus pulposus extrusion: 42 cases (2000–2007). J Am Vet Med Assoc 2009;234:495–504.
  • Fenn J, Drees R, Volk HA, et al. Comparison of clinical signs and outcomes be- tween dogs with presumptive ischemic myelopathy and dogs with acute non- compressive nucleus pulposus extrusion. J Am Vet Med Assoc 2016;249:767–75.
  • Fenn J, Drees R, Volk HA, et al. Inter- and intraobserver agreement for diagnosing presumptive ischemic myelopathy and acute noncompressive nucleus pulposus extrusion in dogs using magnetic resonance imaging. Vet Radiol Ultrasound 2016;57:33–40.
  • Henke D, Gorgas D, Flegel T, et al. Magnetic resonance imaging findings in dogs with traumatic intervertebral disk extrusion with or without spinal cord compression: 31 cases (2006–2010). J Am Vet Med Assoc 2013;242:217–22.
  • McKee WM, Downes CJ, Pink JJ, et al. Presumptive exercise-associated peracute thoracolumbar disc extrusion in 48 dogs. Vet Rec 2010;166:523.
  • Specchi S, Johnson P, Beauchamp G, et al. Assessment of interobserver agreement and use of selected magnetic resonance imaging variables for differentiation of acute noncompressive nucleus pulposus extrusion and ischemic myelopathy in dogs. J Am Vet Med Assoc 2016;248:1013–21.
  • Taylor-Brown FE, De Decker S. Presumptive acute non-compressive nucleus pulposus extrusion in 11 cats: clinical features, diagnostic imaging findings, treatment and outcome. J Feline Med Surg 2015;19:21–6.

 

Last updated by NeuroPetVet on January 23, 2018.