Corticospinal Tract Decussation in the Brainstem
The corticospinal tract crosses at the junction between the medulla oblongata and the spinal cord, forming the pyramidal decussation. 1
Anatomical Location and Structure
The crossing occurs at a highly specific anatomical location:
- The pyramidal decussation is located at the caudal medulla oblongata, where it transitions into the cervical spinal cord 1
- The medulla oblongata is composed of a ventral portion containing the pyramids (where the corticospinal tract fibers are visible as surface landmarks) and a dorsal tegmentum 2
- Most corticospinal tract axons cross the anatomical midline at this pyramidal decussation, though a small percentage remain uncrossed 1
Clinical Significance
Understanding this crossing point is critical for localizing neurological deficits:
- Lesions above the decussation (in the midbrain, pons, or upper medulla) produce contralateral motor deficits because the fibers have not yet crossed 3
- Lesions below the decussation produce ipsilateral motor deficits because the fibers have already crossed to the opposite side 1
- The corticospinal tract descends through the cerebral peduncles in the midbrain, through the ventral pons (pontine basis), and then through the medullary pyramids before decussating 4, 5
Vascular Supply at the Decussation
The region of decussation is supplied by:
- The anterior spinal artery, which branches from the vertebral arteries, supplies the caudal medulla where the pyramidal decussation occurs 5
- The medulla receives additional blood supply from branches of the vertebral arteries and posterior inferior cerebellar arteries 2
This crossing at the pyramidal decussation explains the fundamental principle of contralateral motor control in the human nervous system, where the left motor cortex controls the right side of the body and vice versa.