Central Canal

The central canal is a narrow longitudinal channel located near the center of the spinal cord. It represents the caudal continuation of the ventricular system of the brain and is derived embryologically from the lumen of the neural tube.

The canal contains a small amount of cerebrospinal fluid (CSF) and is lined by ependymal cells. Superiorly, it is continuous with the cavity of the fourth ventricle near the caudal brainstem. It then extends through the spinal cord toward its inferior end.

Although the central canal is anatomically part of the CSF-containing ventricular system, it is extremely small in adults and may become narrowed or partially obliterated with age. Most circulating CSF surrounds the brain and spinal cord within the subarachnoid space rather than passing through the central canal.

Location

The central canal lies within the central region of the spinal cord. In transverse section, it is located within the gray commissural region between the right and left halves of the spinal cord.

Its precise shape and dimensions vary between spinal levels and among individuals.

Relationship to the Gray Commissure

The canal is surrounded by the gray commissure, which connects the gray matter of the two sides of the spinal cord.

This relationship makes the central canal an important landmark when identifying spinal cord anatomy in transverse sections.

Relationship to the Anterior White Commissure

The anterior white commissure lies anterior to the central gray region and central canal.

Crossing axons from several spinal pathways pass through this white matter region, including fibers associated with the anterolateral system.

Superior Continuity

Superiorly, the central canal is continuous with the ventricular system near the fourth ventricle at the transition between the medulla and spinal cord.

This continuity reflects the common embryological origin of the cerebral ventricles and spinal central canal from the lumen of the neural tube.

Inferior Extent

The central canal extends inferiorly through the spinal cord toward the region of the conus medullaris.

Near the inferior end of the spinal cord, the canal may show a small localized expansion traditionally called the terminal ventricle.

Terminal Ventricle

The terminal ventricle, or ventriculus terminalis, is a small cavity that may be present within the conus medullaris near the distal end of the central canal.

It is more prominent during development and is usually very small or inconspicuous in adults.

Structure

The central canal is a very small tube rather than a large ventricular cavity. Its lumen is surrounded by specialized glial cells and adjacent spinal cord tissue.

The size and patency of the canal vary considerably, particularly with age.

Ependymal Lining

The central canal is lined by ependymal cells, the same general cell type that lines the ventricular cavities of the brain.

Ependymal cells form an epithelial-like layer separating the canal lumen from surrounding neural tissue.

Ependymal Cells

Ependymal cells are glial cells derived from neuroepithelial cells of the developing neural tube.

They line the cerebral ventricles and central canal and contribute to the specialized interface between cerebrospinal fluid and nervous tissue.

Periependymal Region

Immediately surrounding the ependymal lining is a region of neural and glial tissue sometimes described as the periependymal region.

This area lies centrally within the spinal gray matter and is closely related to commissural and autonomic spinal cord networks.

Cerebrospinal Fluid

The central canal can contain CSF, but its contribution to overall CSF circulation is small compared with the ventricular cavities and subarachnoid space.

The majority of CSF produced within the cranial ventricular system ultimately enters the subarachnoid space and circulates around the brain and spinal cord.

Position within the Ventricular System

The central canal represents the most caudal component of the continuous internal cavity derived from the neural tube.

The major CSF-containing spaces can be arranged anatomically as:

1. Lateral ventricles
2. Interventricular foramina
3. Third ventricle
4. Cerebral aqueduct
5. Fourth ventricle
6. Central canal and subarachnoid pathways

Fourth Ventricle

The fourth ventricle lies between the brainstem and cerebellum. At its caudal end, the ventricular cavity narrows toward the central canal.

Most CSF leaves the fourth ventricle through its median and lateral apertures to enter the subarachnoid space.

Median Aperture

The median aperture of the fourth ventricle allows CSF to pass into the subarachnoid space, particularly toward the cerebellomedullary cistern.

This is one of the principal routes by which ventricular CSF enters the external CSF circulation.

Lateral Apertures

The paired lateral apertures also connect the fourth ventricle with the subarachnoid space.

Consequently, the central canal is not the primary route for CSF leaving the fourth ventricle.

Central Canal and Subarachnoid Space

The central canal and subarachnoid space both contain CSF but differ greatly in size and functional importance.

The subarachnoid space surrounds the spinal cord and contains the major volume of spinal CSF, while the central canal is a minute internal channel within the cord itself.

Central Canal Compared with Subarachnoid Space

Feature	Central Canal	Spinal Subarachnoid Space
Location	Within spinal cord	Surrounds spinal cord
Size	Very small	Relatively large CSF space
Lining	Ependymal cells	Bounded by arachnoid and pia-related surfaces
CSF role	Minor internal CSF-containing channel	Major pathway for spinal CSF circulation

Embryological Development

The central canal develops from the lumen of the embryonic neural tube.

During neurulation, the neural plate folds to form the neural tube. The cavity enclosed within this tube persists and becomes the ventricular system within the brain and the central canal within the spinal cord.

Neural Tube Lumen

The lumen of the neural tube undergoes extensive regional modification during development.

In the cranial region, expansion produces the ventricular cavities associated with the developing brain vesicles. In the spinal region, the lumen remains relatively narrow and becomes the central canal.

Development of the Ependymal Layer

Neuroepithelial cells lining the neural tube give rise to several neural cell populations during development.

Cells remaining adjacent to the ventricular and central canal surfaces differentiate into the ependymal lining.

Age-Related Changes

The central canal is generally more clearly patent during early life. With increasing age, portions may become narrowed or obliterated.

Therefore, the canal may not form a continuously open channel throughout the entire adult spinal cord.

Central Canal at Different Spinal Levels

The shape and position of the central canal can vary slightly between cervical, thoracic, lumbar, and sacral spinal cord levels.

Despite these variations, it remains closely associated with the central gray commissural region.

Cervical Spinal Cord

In the cervical cord, the central canal lies near the center of the characteristic large transverse spinal cord profile.

It is surrounded by gray matter between the anterior and posterior horns.

Thoracic Spinal Cord

At thoracic levels, the canal remains within the central gray matter and is related to the narrower gray horns and lateral horn region characteristic of much of the thoracic cord.

Lumbar Spinal Cord

At lumbar levels, the canal remains within the broad central gray matter associated with the enlarged anterior and posterior horns of the lumbosacral enlargement.

Conus Medullaris

The conus medullaris is the tapered inferior end of the spinal cord.

The central canal continues into this region and may expand slightly as the terminal ventricle before ending.

Histology

Histologically, the central canal appears as a small lumen surrounded by ependymal cells.

The appearance of the lumen can vary from round or oval to narrow and irregular, particularly in adult tissue where partial obliteration is common.

CSF Production

The central canal is not a major site of CSF production.

Most CSF is produced by the choroid plexuses within the cerebral ventricles. The canal primarily represents a small CSF-containing continuation of the ventricular cavity.

CSF Circulation

A simplified route of CSF circulation is:

1. CSF is produced predominantly by the choroid plexuses of the ventricles.
2. It passes from the lateral ventricles through the interventricular foramina into the third ventricle.
3. It flows through the cerebral aqueduct into the fourth ventricle.
4. Most CSF exits the fourth ventricle through the median and lateral apertures.
5. It circulates through the cranial and spinal subarachnoid spaces.
6. A small amount may occupy the central canal where the canal remains patent.

Functional Significance

The central canal is primarily significant as an anatomical remnant and continuation of the embryonic neural tube lumen and ventricular system.

Its small size means that it does not provide the major pathway for CSF circulation around the spinal cord.

Clinical Significance

Syringomyelia

Syringomyelia is characterized by formation of a fluid-filled cavity, or syrinx, within the spinal cord.

A syrinx commonly develops near the central portion of the cord and can expand to damage surrounding neural structures. It is not simply synonymous with normal dilation of the central canal.

Hydromyelia

Hydromyelia refers more specifically to abnormal dilation of the ependymal-lined central canal.

In practice, the terms hydromyelia and syringomyelia may overlap because abnormal intramedullary cavities can have complex morphology and relationships to the central canal.

Syringohydromyelia

The term syringohydromyelia may be used when an intramedullary cavity has features or relationships that make a strict distinction between syringomyelia and hydromyelia difficult.

Central Cord Damage

An expanding cavity near the central canal can initially damage structures close to the center of the spinal cord.

These may include crossing fibers in the anterior white commissural region and nearby gray matter.

Spinothalamic Fiber Involvement

Pain and temperature fibers entering the spinal cord synapse in the dorsal horn and second-order axons cross through the anterior white commissural region.

A central spinal cord lesion can interrupt these crossing fibers, producing characteristic segmental sensory abnormalities.

Syringomyelia and Sensory Loss

Central cavitation can produce bilateral loss of pain and temperature sensation over affected spinal segments while initially preserving modalities carried in other pathways.

The distribution depends on the level and extent of the cavity.

Expansion of a Syrinx

As a syrinx enlarges, it may affect anterior horn cells, corticospinal pathways, autonomic neurons, posterior columns, and other spinal structures.

Clinical findings therefore become more extensive as the lesion expands beyond the central cord.

Chiari Malformation Association

Syringomyelia can occur in association with abnormalities affecting CSF dynamics at the craniocervical junction, including Chiari malformations.

The relationship emphasizes that pathological spinal cord cavities may be influenced by altered CSF flow outside the central canal itself.

Central Canal Dilatation

Small persistent or mildly prominent portions of the central canal may occasionally be identified on spinal MRI.

The clinical importance depends on morphology, extent, associated abnormalities, and the patient's neurological findings.

Imaging

The normal central canal is often too small to be clearly visualized along its entire length on routine magnetic resonance imaging.

Abnormal dilation or a larger intramedullary fluid cavity is much more readily detected on MRI.

MRI of Syrinx Formation

MRI is the principal imaging technique for evaluating suspected spinal cord cavitation.

It can demonstrate the location, length, diameter, and relationship of a cavity to surrounding spinal cord tissue and can identify associated abnormalities at the craniocervical junction or elsewhere.

Central Canal Compared with Cerebral Aqueduct

Feature	Central Canal	Cerebral Aqueduct
Location	Spinal cord	Midbrain
Connects	Caudal ventricular system with spinal canal lumen	Third and fourth ventricles
Relative size	Extremely small, often partly obliterated in adults	Narrow but normally patent CSF channel
Clinical obstruction	Not a major cause of cranial hydrocephalus	Obstruction can cause noncommunicating hydrocephalus

Central Canal Compared with Fourth Ventricle

Feature	Central Canal	Fourth Ventricle
Location	Spinal cord	Between brainstem and cerebellum
Size	Minute	Large ventricular cavity
Lining	Ependymal	Ependymal
Major CSF outlet	None	Median and lateral apertures
Embryological origin	Neural tube lumen

Key Anatomical Features

Feature	Key Point
Structure	Narrow longitudinal channel
Location	Central spinal cord
Surrounding region	Gray commissure
Lining	Ependymal cells
Contents	Small amount of CSF when patent
Superior continuity	Fourth ventricular system
Inferior region	Conus medullaris and terminal ventricle
Embryological origin	Lumen of neural tube
Adult appearance	Often narrowed or partially obliterated
Major clinical association	Hydromyelia and central spinal cord cavitation

Anatomical Importance

The central canal represents the spinal continuation of the internal cavity of the developing central nervous system. Its continuity with the ventricular system reflects the shared origin of the brain and spinal cord from the neural tube.

In the mature nervous system, the canal is a minute ependymal-lined structure within the central gray matter of the spinal cord. It contains only a small amount of CSF where patent, while the much larger subarachnoid space provides the principal route for CSF circulation around the spinal cord.

Its greatest clinical importance comes from its relationship to central spinal cord pathology. Abnormal dilation of the canal or development of a nearby syrinx can injure crossing and segmental neural pathways, producing characteristic neurological deficits as the cavity expands.