An 81 -year-old female with critical aortic stenosis has a valve replacement procedure. Post-operatively
she is diagnosed with an anterior spinal artery syndrome at the T6-T7 level on an MRI.

a) Describe the signs you would expect on sensory examination of her lower limbs.    (20% marks)
b) What are the deep tendon reflexes likely to show?    (20% marks)
c) What perioperative factors may contribute to this syndrome?    (30% marks)
d) What therapies have been advocated to optimise spinal cord perfusion? (30% marks)

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College answer

  1. Sensory neurological examination of the lower limbs would reveal loss of pain and temperature sensation with a sensory level of T6-T7 with relative sparing of proprioception and vibratory sense below this level. 
  1. The acute stages are characterised by flaccidity and loss of deep tendon reflexes (with spasticity and hyperreflexia developing over ensuing days and weeks). 
  1. Prolonged aortic cross clamp ,low perfusion pressure to the spinal cord as well as IABP, or ECMO  are associated with spinal infarction 
  1. Mean arterial pressure is increased in increments of 10mm Hg every five minutes (with volume and vasopressor agents) until symptoms resolve, bleeding complications ensue, or additional blood pressure augmentation would cause an unacceptably high risk of bleeding at the surgical bed.

If a lumbar drain is in place, it should be opened and set to drain at 8 to 12mm Hg. If not in place, a lumbar drain should be placed if there is no response to blood pressure augmentation within 10 to 20 minutes.  

Discussion

a)

The sensory signs of an anterior spinal artery syndrome are:

  • Preserved bilateral proproception and vibration
  • Lost bilateral pain, temperature
  • Usually, preserved light touch sensation (Triggs & Beric, 1992)

There would also be bilaterally absent motor control, and probably incontinence. The affected tracts are:

  • Anterior spinothalamic tract (pain)
  • Vestibulospinal tract (postural motor control)
  • Tectospinal tract (reflexive postural head neck and eye movements)
  • Anterior reticulospinal tract (postural motor control)
  • Anterior corticospinal tract (gross motor control)

b)

Tendon reflex examination would reveal a flaccid loss of reflexes. "Flaccid motor paralysis and absent deep tendon reflexes may later progress to spasticity and hyperactive tendon reflexes", say Santamato et al (2013), but they do not say how long it will take. Spinal reflex arcs below the level of the injury will be intact, but they are facilitated by input from upper motor neurons and when this is interrupted the deep tendon reflexes are transiently lost.

c)

Perioperative factors in cardiothoracic or abdominal aortic surgery which promotes anterior spinal artery syndrome are

  • Perioperative hypotension
  • Prolonged aortic crossclamp time
  • Other instrumentation of the atheromatous aorta (eg. angiography, IABP, VA ECMO)
  • Inadequate heparinisation of the bypass circuit
  • Air emboli

Apart from "perioperative factors", Djurberg & Haddad (1995) list "conditions affecting blood flow in the anterior spinal artery":

  • Arteriosclerosis
  • Vascular malformations (aortic aneurysms, haemangioma etc.)
  • Tumour
  • Infection (tuberculosis)
  • Haematological disorders (polycythaemia, hypercoagulability)
  • Trauma of the spine (fracture. haematoma, foreign body etc.)
  • Chronic respiratory disease with polycythaemia
  • Anatomical changes of the spine (kyphoscoliosis, spondyloarthrosis, disc herniation etc.)

d)

Management of an infarcted anterior cord involves maximising the perfusion of the cord via collaterals. The best information about this about this seems to come from Hnath et al (2007), who published a fairly successful protocol. This consisted of:

  • Increasing perfusion pressure
    • Hnath et al maintained the MAP  at ≥90 mm Hg. In their answer, the college  examiners recommend cranking the vasopressors until symptoms resolve or complications develop. This comes from the "Spinal Cord Infarction" UpToDate article by Mullen et al (2016).
  • Decreasing spinal CSF pressure 
    • Hnath et al actively drained the CSF to maintain pressures <15 mm Hg. The college recommend simply draining to a positive pressure of no more than 8-12 mmHg, which is again from the same UpToDate source. The systematic review by Cina et al (2004) suggests that if you're going to do this, you should aim to decrease the CSF pressure to at least below 10 mmHg, for at least 48-60 hours. The rationale for this is that the lower CSF pressure minimise the resistance to afferent spinal cord blood flow, thereby increasing perfusion of at-risk regions (Strohm et al, 2017)

Hnath et al reported a 60% improvement, but their series had only 5 patients in the treatment arm, which somewhat dampens the enthusiasm of anybody following their footsteps. Chiesa et al (2005) list several other possible strategies:

  • Distal aortic perfusion by bypass of the left heart (i.e. piping oxygenated blood into the distal aorta), which doesn't seem to work according to Coselli et al (2004)
  • Deep hypothermic circulatory arrest which should theoretically protect the cord perioperatively (Safi et al, 1998)
  • Regional cooling of the cord by infusing normal saline at 4° C into a thoracic epidural (Cambria et al, 1997)
  • Protective pharmacological agents, used perioperatively (steroids, naloxone, barbiturates, papaverine, magnesium sulfate)

References

Djurberg, H., and M. Haddad. "Anterior spinal artery syndrome." Anaesthesia 50.4 (1995): 345-348.

Eltorai, Ibrahim M. "Anterior Spinal Artery Syndrome." Rare Diseases and Syndromes of the Spinal Cord. Springer, Cham, 2016. 437-440.

Foo, Dominic, and Alain B. Rossier. "Anterior spinal artery syndrome and its natural history." Spinal Cord 21.1 (1983): 1.

Zuber, William F., Max R. Gaspar, and Philip D. Rothschild. "The anterior spinal artery syndrome--a complication of abdominal aortic surgery: report of five cases and review of the literature.Annals of surgery 172.5 (1970): 909.

TRIGGS, WILLIAM J., and ALEKSANDAR BERIĆ. "Sensory abnormalities and dysaesthesias in the anterior spinal artery syndrome." Brain 115.1 (1992): 189-198.

Aydin, A. "Mechanisms and prevention of anterior spinal artery syndrome following abdominal aortic surgery." Angiologiia i sosudistaia khirurgiia= Angiology and vascular surgery 21.1 (2015): 155-164.

Santamato, Andrea, et al. "Paraplegia due to Anterior Spinal Artery Stroke: Rehabilitative Program on Lower Extremity Weakness and Locomotor Function." Int J Phys Med Rehabil1.118 (2013): 2.

Ullery, Brant W., et al. "Risk factors, outcomes, and clinical manifestations of spinal cord ischemia following thoracic endovascular aortic repair." Journal of vascular surgery 54.3 (2011): 677-684.

Cheshire, William P., et al. "Spinal cord infarction Etiology and outcome." Neurology 47.2 (1996): 321-330.

Gialdini, Gino, et al. "Retrospective analysis of Spinal Cord Infarction after Aortic Repair (P6. 300)." Neurology 88.16 Supplement (2017): P6-300.

Hnath, Jeffrey C., et al. "Strategies to improve spinal cord ischemia in endovascular thoracic aortic repair: outcomes of a prospective cerebrospinal fluid drainage protocol." Journal of vascular surgery 48.4 (2008): 836-840.

Chiesa, Roberto, et al. "Spinal cord ischemia after elective stent-graft repair of the thoracic aorta." Journal of vascular surgery 42.1 (2005): 11-17.

Strohm, Tamara, Seby John, and Muhammad Hussain. "Cerebrospinal Fluid Drainage for Acute Spinal Cord Infarction (P1. 301)." Neurology 88.16 Supplement (2017): P1-301.

Coselli, Joseph S., et al. "Left heart bypass during descending thoracic aortic aneurysm repair does not reduce the incidence of paraplegia." The Annals of thoracic surgery 77.4 (2004): 1298-1303.

Safi, Hazim J., et al. "Thoracic and thoracoabdominal aortic aneurysm repair using cardiopulmonary bypass, profound hypothermia, and circulatory arrest via left side of the chest incision." Journal of vascular surgery 28.4 (1998): 591-598.

Cambria, Richard P., et al. "Clinical experience with epidural cooling for spinal cord protection during thoracic and thoracoabdominal aneurysm repair." Journal of vascular surgery 25.2 (1997): 234-243.

Cinà, Claudio S., et al. "Cerebrospinal fluid drainage to prevent paraplegia during thoracic and thoracoabdominal aortic aneurysm surgery: a systematic review and meta-analysis." Journal of vascular surgery 40.1 (2004): 36-44.

Taira, Yutaka, and Martin Marsala. "Effect of proximal arterial perfusion pressure on function, spinal cord blood flow, and histopathologic changes after increasing intervals of aortic occlusion in the rat." Stroke 27.10 (1996): 1850-1858.

Mullen, Michael, et al. "Spinal cord infarction: Prognosis and treatment." UpToDate. Waltham MA.(Accessed on February, 2016).