Anatomy and blood supply of Spinal Cord

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Anatomy and Blood Supply of the Spinal Cord

1. General Overview

The spinal cord is a cylindrical extension of the brainstem that passes through the vertebral canal. It is shorter than the vertebral column, terminating as the conus medullaris at approximately L1-L2 in adults (L3 in neonates). From the conus, a fibrous strand - the filum terminale - descends to attach to the dorsum of the first coccygeal segment.

The cord is enclosed in three meningeal layers:

Pia mater - innermost, closely adherent
Arachnoid mater - middle layer; separated from pia by the subarachnoid space (contains CSF)
Dura mater - outermost tough layer

2. Spinal Cord Segments and Nerve Roots

The cord gives rise to 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal).

Key rule for nerve root exit:

C1-C7: exit above the pedicle for which they are named (C6 root exits between C5 and C6 pedicles)
C8: exits between C7 and T1 pedicles
T1 and below: exit below the pedicle for which they are named (L4 root exits between L4 and L5 pedicles)

Because the cord is shorter than the column, lumbar and sacral roots travel long distances inside the canal before exiting, forming the cauda equina below the conus.

3. External Features

Feature	Details
Cervical enlargement	C4-T1; for the brachial plexus/upper limb
Lumbosacral enlargement	L1-S3; for the lumbosacral plexus/lower limb
Anterior median fissure	Deep midline groove on ventral surface
Posterior median sulcus	Shallow midline groove on dorsal surface
Anterolateral sulcus	Exit of ventral (motor) roots
Posterolateral sulcus	Entry of dorsal (sensory) roots

4. Internal Structure - Cross-Sectional Anatomy

Cross-section of spinal cord showing gray and white matter, dorsal/ventral horns, and nerve roots (Neuroanatomy through Clinical Cases)

Basic spinal cord anatomy showing gray matter, white matter, dorsal and ventral roots - Neuroanatomy through Clinical Cases, 3rd Ed.

A. Gray Matter (H- or butterfly-shaped)

The gray matter has a characteristic "H" shape with two lateral columns joined by a gray commissure. It contains:

Dorsal (posterior) horn - primarily sensory processing Ventral (anterior) horn - contains lower motor neurons (LMNs); more prominent at cervical and lumbosacral enlargements Intermediate zone - interneurons and specialized nuclei Intermediolateral (IML) column - T1 to L2 only; preganglionic sympathetic neurons Sacral parasympathetic nucleus - S2-S4; preganglionic parasympathetic neurons

Rexed's Laminae (10 laminae):

Laminae	Region	Function
I	Dorsal horn (marginal zone)	Pain & temperature
II	Dorsal horn (substantia gelatinosa)	Pain modulation
III-IV	Dorsal horn (nucleus proprius)	Touch, proprioception relay
V	Dorsal horn	Wide dynamic range neurons
VI	Dorsal horn (base)	Proprioceptive input
VII	Intermediate zone	Clarke's column (T1-L2), IML, interneurons
VIII-IX	Ventral horn	Motor interneurons, alpha/gamma LMNs
X	Around central canal	Gray commissure

B. White Matter (surrounds gray matter)

Three funiculi (columns) on each side:

Dorsal (posterior) funiculus - between posterior horns; carries the dorsal column medial lemniscal system

Fasciculus gracilis (medial): from lower body (below T6) - fine touch, vibration, proprioception
Fasciculus cuneatus (lateral): from upper body (above T6) - same modalities; only present at cervical levels

Lateral funiculus - between dorsal and ventral horns; contains:

Lateral corticospinal tract (descending, main motor pathway - 85%)
Rubrospinal tract (descending)
Lateral spinothalamic tract (ascending - pain, temperature)
Dorsal and ventral spinocerebellar tracts

Ventral (anterior) funiculus - between ventral horns and anterior median fissure; contains:

Anterior corticospinal tract (descending - 15%)
Vestibulospinal, tectospinal, reticulospinal tracts (descending)
Anterior spinothalamic tract (crude touch, pressure)

Cross-section showing tract lamination with S=sacral, L=lumbar, Th=thoracic, C=cervical arrangement (Localization in Clinical Neurology)

Tract lamination: fibers in the dorsal columns and spinothalamic tracts are arranged somatotopically - sacral most lateral, cervical most medial/anterior. This explains clinical differences between central cord syndrome (affects cervical fibers first) and peripheral cord lesions - Localization in Clinical Neurology, 8e.

5. Variation by Level

Level	White Matter	Gray Matter	Notable
Cervical	Most abundant (all ascending fibers present, most descending not yet terminated)	Enlarged ventral horn	Fasciculus cuneatus present
Thoracic	Moderate	Relatively small	IML column present
Lumbar	Less	Large (especially ventral horn)	No IML
Sacral	Least	Mostly gray	Parasympathetic nucleus

6. Blood Supply of the Spinal Cord

The spinal cord has both an extrinsic and an intrinsic vascular network.

A. The Three Longitudinal Arteries

Overview of spinal cord blood supply showing anterior spinal artery, posterior spinal arteries, artery of Adamkiewicz, and segmental input from the aorta (Miller's Anesthesia)

Complete overview of spinal cord arterial supply showing the anterior spinal artery, posterior spinal arteries, radiculomedullary arteries, and the artery of Adamkiewicz - Miller's Anesthesia, 10e.

1. Anterior Spinal Artery (ASA) - Single

Formed by fusion of two branches from the terminal vertebral arteries at the cervicomedullary junction
Runs the entire length of the cord in the anterior median fissure
Supplies the anterior 2/3 of the cord via:
- Sulco-commissural (central) arteries - penetrate deeply to supply anterior gray columns, lateral gray columns, and ventral white matter
- Pial radial network - supplies peripheral rim of the anterior white matter

2. Posterior Spinal Arteries (PSA) - Paired

Arise from the vertebral arteries or posterior inferior cerebellar arteries (PICA)
Run bilaterally along the posterolateral surfaces of the cord
Supply the posterior 1/3 of the cord - the dorsal columns and dorsal horns
Form a rich anastomotic spinal arterial plexus around the cord (the vasocorona)
Relatively protected from ischemia because of the dual supply (two PSAs vs one ASA)

B. Radiculomedullary (Segmental) Arteries - Extrinsic Input

The longitudinal spinal arteries are reinforced along their length by radiculomedullary arteries that enter through the intervertebral foramina alongside nerve roots. Of the 31 segmental arteries, only 6-10 are true radiculomedullary arteries that actually reach the cord.

Lazorthes divided these into three groups:

Group	Level	Source
Upper (cervicothoracic)	C1-T2	Vertebral, ascending cervical, thyrocervical, and costovertebral arteries
Middle (thoracic)	T3-T8	Usually a single T7 radicular artery from aorta
Lower (thoracolumbar)	T9-L2	Artery of Adamkiewicz

Segmental and radicular arterial supply showing sulcal arteries, penetrating arteries, and the artery of Adamkiewicz at T10-L1 (Adams & Victor's)

Detailed view of segmental arterial supply - note the artery of Adamkiewicz entering at T10-L1 and joining the anterior spinal artery - Adams & Victor's Principles of Neurology, 12e.

C. Artery of Adamkiewicz (Arteria Radicularis Magna)

The largest and most important anterior radiculomedullary artery
Supplies the lower 2/3 of the anterior spinal artery territory (including the lumbosacral enlargement)
Origin: typically from a left posterior intercostal artery arising from the descending aorta, usually between T9 and T12 (range: T7-L5)
Its characteristic hairpin configuration on angiography/imaging is pathognomonic
Because it is the sole major supply to the lower thoracic cord, this region is a watershed zone highly susceptible to ischemia during aortic surgery or hypotension

D. Additional Sources by Region

Region	Arterial Source
Cervical cord	Vertebral arteries, ascending cervical and deep cervical (thyrocervical trunk)
Thoracic cord	Segmental posterior intercostal arteries from aorta
Lumbar cord	Lumbar segmental arteries from aorta
Sacral cord	Median sacral artery, lateral sacral arteries (internal iliac)

E. Intrinsic Cord Vessels (Cross-section)

Cross-section showing ASA territory (anterior 2/3) vs PSA territory (posterior 1/3) with the spinal arterial plexus

Cross-sectional vascular territories: the ASA supplies the anterior 2/3 (yellow-tan); the PSAs supply the dorsal third (green). The peripheral rim is supplied by the pial arterial plexus (vasocorona) - Neuroanatomy through Clinical Cases, 3rd Ed.

7. Venous Drainage

Six longitudinal venous channels run the cord's length (anterior and posterior median veins, anterolateral and posterolateral veins)
These drain via anterior and posterior radicular veins into the internal vertebral venous plexus (Batson's plexus) in the epidural space
From there, drainage proceeds to the external vertebral plexus and then into the azygos/hemiazygos system, iliac veins, and inferior vena cava

8. Clinical Correlations

Vascular Syndrome	Artery	Cord Region Affected	Clinical Features
Anterior spinal artery syndrome	ASA	Anterior 2/3 (spinothalamic + corticospinal + anterior horn)	Bilateral weakness, loss of pain/temperature; preserved vibration/proprioception (dorsal columns spared)
Posterior spinal artery syndrome	PSA	Posterior 1/3 (dorsal columns)	Loss of vibration, proprioception, fine touch; weakness may occur
Adamkiewicz occlusion	Artery of Adamkiewicz	Lower thoracic/lumbar cord	Paraplegia with anterior cord syndrome; common in aortic surgery
Watershed infarction	T3-T8	Mid-thoracic cord (least collateral flow)	Paraplegia; most common location of spinal cord infarct

Sources:

Campbell's Operative Orthopaedics, 15th Ed. (2026), p. 2225
Neuroanatomy through Clinical Cases, 3rd Ed., pp. 250-253
Adams and Victor's Principles of Neurology, 12th Ed., p. 658-666
Localization in Clinical Neurology, 8th Ed., pp. 242-243
Miller's Anesthesia, 10th Ed., pp. 8015-8017
Bradley and Daroff's Neurology in Clinical Practice

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