Spinal Cord¶
Definition¶
The spinal cord is the major conduit of the central nervous system extending from the brainstem to the conus medullaris, situated within the vertebral (spinal) canal. In adults, the spinal cord typically terminates at the level of L1–L2 (conus medullaris). It is approximately 45 cm long, roughly 1 cm in diameter, and is surrounded by three meningeal layers and cerebrospinal fluid (CSF).
Anatomy¶
External Structure¶
The spinal cord has two prominent enlargements corresponding to the nerve supply of the limbs:
| Enlargement | Levels | Function |
|---|---|---|
| Cervical enlargement | C4–T1 | Brachial plexus — upper extremity innervation |
| Lumbar enlargement | L1–S2 | Lumbosacral plexus — lower extremity innervation |
Key external features include:
- Anterior median fissure — deep groove along the anterior midline
- Posterior median sulcus — shallow groove along the posterior midline
- Anterolateral sulcus — exit point of ventral (motor) nerve roots
- Posterolateral sulcus — entry point of dorsal (sensory) nerve roots
Internal Structure (Cross-Section)¶
The spinal cord in cross-section demonstrates a characteristic butterfly-shaped gray matter core surrounded by white matter:
Gray matter (central):
- Anterior horns — contain lower motor neurons (alpha motor neurons)
- Posterior horns — receive sensory input from dorsal nerve roots
- Lateral horns — present at T1–L2 (sympathetic) and S2–S4 (parasympathetic); contain autonomic neurons
- Central canal — CSF-filled remnant canal in the center
White matter (peripheral):
- Dorsal columns — carry proprioception and fine touch (fasciculus gracilis, fasciculus cuneatus)
- Lateral corticospinal tracts — carry voluntary motor signals
- Spinothalamic tracts — carry pain and temperature sensation
Meningeal Coverings¶
Three meningeal layers surround the spinal cord:
| Layer | Description | Space Below |
|---|---|---|
| Dura mater | Tough outer layer; forms the thecal sac extending to S2 | Epidural space (fat, veins) |
| Arachnoid mater | Thin, avascular middle layer | Subarachnoid space (CSF) |
| Pia mater | Delicate layer adherent to the cord surface | — |
Vascular Supply¶
- Anterior spinal artery (single) — supplies the anterior two-thirds of the cord
- Posterior spinal arteries (paired) — supply the posterior one-third of the cord
- Segmental radicular arteries — reinforce the spinal arteries; the largest is the artery of Adamkiewicz (typically T9–T12 on the left)
Clinical Pearl
The anterior spinal artery supplies the anterior two-thirds of the cord, including the corticospinal tracts and spinothalamic tracts. Occlusion causes anterior cord syndrome — motor paralysis and loss of pain/temperature sensation with preserved posterior column function (proprioception, vibration). See Anterior Spinal Artery Syndrome.
Imaging Findings¶
MRI¶
MRI is the definitive imaging modality for the spinal cord:
| Finding | T1 Signal | T2 Signal | Significance |
|---|---|---|---|
| Normal cord | Intermediate (homogeneous) | Intermediate (homogeneous) | Smooth contours, uniform caliber |
| Cord edema/myelopathy | Low | High | Gliosis, demyelination, ischemia |
| Cord hemorrhage (acute) | Isointense | Low (deoxyhemoglobin) | Trauma, vascular malformation |
| Cord hemorrhage (subacute) | High (methemoglobin) | High | Evolving hemorrhage |
| Syrinx | Dark (CSF signal) | Bright (CSF signal) | Smooth, well-defined intramedullary cavity |
| Cord tumor | Variable | High | Expansion of cord, may enhance with contrast |
| Cord atrophy | — | — | Reduced caliber, may follow chronic myelopathy |
Normal Cord Diameter
The normal spinal cord measures approximately 8–10 mm in AP diameter at the cervical enlargement. Cord diameters less than 7 mm may indicate atrophy. The cord should have a smooth, symmetric contour on sagittal and axial images.
CT Myelography¶
When MRI is contraindicated, CT myelography can evaluate:
- Cord compression by disc, osteophyte, or mass
- Cord atrophy
- Intradural pathology outlined by contrast
Key Points¶
- The spinal cord extends from the brainstem to approximately L1–L2 (conus medullaris)
- Two enlargements (cervical and lumbar) correspond to limb innervation
- Gray matter (central) contains motor and sensory neurons; white matter (peripheral) contains ascending and descending tracts
- The anterior spinal artery supplies the anterior two-thirds of the cord
- MRI is the gold standard — increased T2 signal in the cord indicates myelopathy
- Normal cord AP diameter is 8–10 mm at the cervical enlargement
References¶
- Khan YS, Lui F. Neuroanatomy, Spinal Cord. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2023 Jul 24. PMID: 32644482. https://www.ncbi.nlm.nih.gov/books/NBK559056/
- Ganapathy MK, Reddy V, Tadi P. Neuroanatomy, Spinal Cord Morphology. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2024 Sep 10. PMID: 31424790. https://www.ncbi.nlm.nih.gov/books/NBK545206/
- Harrow-Mortelliti M, Reddy V, Jimsheleishvili G. Physiology, Spinal Cord. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2023 Mar 17. PMID: 31334987. https://www.ncbi.nlm.nih.gov/books/NBK544267/
- Hasan S, Arain A. Neuroanatomy, Spinal Cord Arteries. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2023 Aug 8. PMID: 30969711. https://www.ncbi.nlm.nih.gov/books/NBK539889/
- Lindeire S, Hauser JM. Anatomy, Back, Artery of Adamkiewicz. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated 2025 Mar 25. PMID: 30422566. https://www.ncbi.nlm.nih.gov/books/NBK532971/
- Taterra D, Skinningsrud B, Pękala PA, et al. Artery of Adamkiewicz: a meta-analysis of anatomical characteristics. Neuroradiology. 2019;61(8):869-880. PMID: 31030251. https://pubmed.ncbi.nlm.nih.gov/31030251/
- Winegar BA, Kay MD, Taljanovic M. Magnetic resonance imaging of the spine. Pol J Radiol. 2020;85:e550-e574. PMID: 33101557. https://pmc.ncbi.nlm.nih.gov/articles/PMC7571515/