Anterior Spinal Artery Syndrome

Anterior spinal artery syndrome is the clinical picture of infarction in the territory of the anterior spinal artery, which supplies the anterior two thirds of the spinal cord. It produces flaccid then spastic paraplegia or quadriplegia, loss of pain and temperature sensation, and sphincter dysfunction, with sparing of the dorsal columns.

It is the commonest spinal cord infarction syndrome and accounts for most of the roughly 1 to 2% of strokes affecting the spinal cord. It occurs most often in the thoracic cord, in adults with a mean age of 55 to 60 years.

Causes. Aortic dissection or surgery, hypotension and cardiac arrest, atherosclerosis, embolism, vasculitis, spinal and epidural procedures, sickle cell disease, cocaine and amphetamine use, intervertebral disc herniation and trauma.

Course. Maximum deficit within hours, with the poorest recovery in complete motor loss at presentation; early mobilisation and rehabilitation improve function.

Pathophysiology.

The single anterior spinal artery receives feeder vessels from radicular arteries and has a poor supply at the mid-thoracic level, making the cord vulnerable to low perfusion.

Infarction of the anterior horn, spinothalamic and corticospinal tracts leaves the posterior columns, supplied by the paired posterior spinal arteries, intact.

• Acute onset of severe back or neck pain, often radicular or girdle like.
• Flaccid weakness progressing to spastic paraplegia or quadriplegia caudal to the lesion.
• Loss of pain and temperature caudal to the lesion, with preserved vibration, joint position and light touch.
• Urinary retention and constipation; sexual dysfunction.
• Orthostatic hypotension, bradycardia and autonomic dysreflexia in cervical or high thoracic lesions.

Red flags.

• Cervical lesion with respiratory failure or autonomic instability.
• Signs of aortic dissection: chest or back pain with pulse deficit or blood pressure difference.
• Fever or new spinal tenderness (infection).

• MRI of the spine with diffusion weighted imaging: anterior cord T2 hyperintensity (the "owl's eyes" sign on axial images, or pencil like on sagittal images); repeat MRI after 24 to 48 hours if the first is normal.
• CT or MR angiography of the aorta and spinal arteries; spinal angiography if a malformation is suspected.
• Exclude cord compression, epidural haematoma, abscess and transverse myelitis; lumbar puncture if inflammatory cause is possible.
• ECG, echocardiography, blood pressure review, lipids, glucose, inflammatory markers, thrombophilia screen and sickle cell test.

Differential diagnosis. Transverse myelitis, compressive myelopathy, epidural haematoma, Guillain-Barré syndrome, acute flaccid myelitis, central cord syndrome and neuromyelitis optica spectrum disorder.

• Restore and keep spinal cord perfusion: correct hypotension, hypovolaemia and anaemia, and aim for a mean arterial pressure of at least 85 mmHg for up to 7 days (use vasopressors as needed).
• Urgent treatment of the cause: repair or manage aortic dissection with vascular surgery, treat embolic sources, and stop vasoconstrictive drugs.
• Lumbar drainage of cerebrospinal fluid after aortic repair, to keep pressure at or under 10 mmHg.
• Aspirin 300 mg orally (or rectally if swallowing is impaired) once, then 75 mg daily, after haemorrhage is excluded. Maximum 300 mg daily. Monitor for gastrointestinal bleeding. Avoid in active bleeding, peptic ulcer and aspirin hypersensitivity; use caution in asthma and renal impairment.
• Atorvastatin 80 mg orally once daily at night. Maximum 80 mg daily; limit to 20 mg daily with clarithromycin. Monitor liver function and creatine kinase; avoid in active liver disease and pregnancy.
• Thromboprophylaxis: enoxaparin 40 mg subcutaneously once daily. Maximum 40 mg daily (20 mg daily when creatinine clearance is under 30 mL/min). Monitor platelets, renal function and bleeding. Avoid in active bleeding.
• Bladder care (intermittent catheterisation), bowel programme, pressure area care, early mobilisation and spasticity management with baclofen 5 mg orally three times daily, increased by 5 mg every 3 days to a usual 30 to 75 mg daily (maximum 100 mg daily); monitor sedation and weakness, reduce dose in renal impairment, and withdraw slowly.
• Treat autonomic dysreflexia by sitting the patient up, removing the trigger (bladder, bowel) and lowering blood pressure if it stays over 150 mmHg systolic.
• Intensive rehabilitation and psychological support.

Monitoring. Hourly neurological and blood pressure checks for 24 hours; review at 4 to 6 weeks, 3 months and 12 months.

Referral and escalation. Neurology, vascular surgery and spinal rehabilitation; intensive care for respiratory failure.

Special groups. Post-surgical patients: perfusion targets and drainage. Children: usually from malformation or trauma.