The anatomical course of the pyramidal tract and signs of its lesion

1. Big picture

The pyramidal tract is the main descending motor pathway for voluntary, skilled movement, especially fine movements of the distal limbs. Clinically, it is the most important pathway behind the concept of an upper motor neuron lesion.

For the exam, the key is not only to know the anatomy, but to use it for localization:

• Lesion above the pyramidal decussation → motor signs on the contralateral side of the body.

• Lesion below the pyramidal decussation, in the spinal cord → motor signs on the ipsilateral side below the lesion.

• Lesion in the brainstem → often gives crossed signs: ipsilateral cranial nerve lesion + contralateral pyramidal weakness.

• Lesion of the pyramidal tract causes central type paresis: weakness, increased deep tendon reflexes, spasticity, pathological reflexes, and loss of superficial reflexes.

The examiner usually wants you to describe the course from the cortex to the spinal cord, then explain why pyramidal tract damage produces spastic paresis and pyramidal signs.