Anatomy of the Spinal Cord
Structural Organization
The spinal cord is a cylindrical neural structure extending from the foramen magnum to approximately the L2 vertebral level, organized into distinct gray and white matter regions with specific functional tracts that enable bidirectional communication between the brain and peripheral nervous system 1, 2.
Gross Anatomy
The spinal cord measures approximately 140 mL in volume and is divided into cervical, thoracic, and lumbar segments 3. The cord is covered by three protective meningeal layers from outermost to innermost:
- Dura mater (outermost)
- Arachnoid mater (middle layer)
- Pia mater (innermost, directly adherent to cord surface)
The subarachnoid space between the arachnoid and pia mater contains cerebrospinal fluid (CSF), which is produced at approximately 800 mL per 24 hours by the choroid plexus, replacing the entire CSF volume more than 5 times daily 3.
Cross-Sectional Anatomy
On axial imaging, the spinal cord demonstrates:
White Matter (Peripheral):
- Lateral columns - contain the lateral corticospinal tract (motor) and lateral spinothalamic tract (pain/temperature sensation)
- Dorsal (posterior) columns - contain ascending sensory pathways for proprioception and fine touch
- Anterior white matter - contains descending motor pathways 4, 5
Gray Matter (Central):
- Anterior horns - contain lower motor neurons
- Posterior horns - contain sensory processing neurons
- Central gray matter - forms an H or butterfly shape on axial sections 4, 5
Vascular Supply
The anterior spinal artery supplies the anterior two-thirds of the cord and is particularly vulnerable to ischemic injury 6. The artery of Adamkiewicz (AKA) is the critical radiculomedullary artery that typically arises from T9-L2 (75% of cases), though it can originate anywhere from T5-L2. Key anatomic features include:
- The AKA arises from the left side in 85% of cases
- It forms a characteristic "hairpin" loop when joining the anterior spinal artery
- 74% of individuals have only one AKA, while 26% have 2-3 6
The posterior spinal arteries (paired) supply the posterior one-third of the cord and receive more segmental arterial contributions than the anterior spinal artery, making the posterior cord less susceptible to ischemia 6.
Regional Variations
Cervical cord - Most frequently involved in pathology, contains enlarged gray matter for upper extremity innervation 4
Thoracic cord - Narrower diameter, contains sympathetic preganglionic neurons in the lateral horn
Lumbar/conus region - Contains high concentration of lower motor neurons, demonstrates greatest potential for neurologic recovery after injury due to "root escape" phenomenon 7
Clinical Imaging Correlates
On MRI, normal spinal cord anatomy appears as:
- Cord diameter typically less than half the spinal canal width
- Gray matter visible as central butterfly configuration on high-resolution sequences
- White matter tracts identifiable on advanced sequences (DTI, magnetization transfer) 8, 2
Pathologic lesions affecting specific anatomic regions produce characteristic clinical syndromes - lateral column involvement causes motor deficits, posterior column involvement causes proprioceptive loss, and anterior cord involvement produces motor and pain/temperature deficits while sparing proprioception 4, 9, 10.
Understanding these anatomic relationships is essential for lesion localization, as decussation points of white matter tracts help determine lesion level, and distinct patterns of gray versus white matter involvement narrow differential diagnoses 9, 10.