What spinal tract is affected first by an expansile lesion in the central canal of the spine?

Spinal Tract Affected First by an Expansile Lesion in the Central Canal

The spinothalamic tract is typically affected first by an expansile lesion in the central canal of the spine due to its anatomical proximity to the central gray matter. 1

Anatomical Considerations

• The spinal cord consists of centrally located gray matter surrounded by white matter tracts, with the central canal running through the middle of the gray matter 1
• An expansile lesion originating in the central canal will first affect the structures closest to it, which are the central gray matter and adjacent white matter tracts 2
• The spinothalamic tract, which carries pain and temperature sensation, is located in the anterolateral portion of the spinal cord white matter but has fibers that cross through the anterior commissure near the central canal 1

Pathophysiological Progression

• Expansile lesions in the central canal initially cause compression of the central gray matter before extending to affect the surrounding white matter tracts 2
• As the lesion expands, it typically follows the path of least resistance, affecting:
  1. Central gray matter (immediately surrounding the central canal) 2
  2. Crossing fibers of the spinothalamic tract (pain and temperature) 1
  3. Adjacent white matter tracts based on proximity 2

Clinical Manifestations

• Early symptoms of central canal expansile lesions often include:
  • Dissociated sensory loss (loss of pain and temperature sensation with preservation of touch and proprioception) due to involvement of the spinothalamic tract 1
  • Bilateral symptoms in a suspended "girdle" distribution due to damage to commissural fibers crossing near the central canal 1
  • Preservation of dorsal column function (touch, vibration, proprioception) until later stages 1

Imaging Findings

• MRI is the preferred method for evaluating spinal cord lesions, with central canal lesions typically showing:
  • T2 hyperintensity centered around the central canal 3
  • Expansion of the central canal with compression of surrounding structures 3
  • Possible enhancement with contrast depending on the lesion type 3

Pathological Considerations

• The rate of white matter versus gray matter damage differs in spinal cord pathology:
  • Gray matter is generally more vulnerable to initial compression 2
  • White matter tracts show more delayed pathological changes following injury 4
  • Compression exceeding 50% results in severe injuries to both gray and white matter 2

Important Clinical Correlations

• Damage to the spinothalamic tract results in contralateral loss of pain and temperature sensation below the level of the lesion 1
• As the lesion expands, it may subsequently affect:
  • Corticospinal tracts (motor function) 1
  • Posterior columns (touch, vibration, proprioception) 1
  • Autonomic pathways (when there is bilateral cord involvement) 1

Diagnostic Approach

• MRI is the gold standard for evaluating central canal lesions, with recommended protocols including:
  • Sagittal and axial T1 and T2-weighted sequences 3
  • Contrast enhancement to evaluate for blood-spinal cord barrier disruption 3
  • Phase sensitive inversion recovery (PSIR) sequences may help better delineate gray-white matter involvement 5