Central Canal

The central canal is a slender, cerebrospinal fluid-filled channel extending throughout the length of the spinal cord. As the residual lumen of the embryonic neural tube, it forms a structural and functional link between the spinal cord and the ventricular system of the brain. Although prominent in early life, the canal commonly becomes narrowed or completely occluded with age. Its structure, microscopic features and clinical significance remain important in understanding spinal cord anatomy and associated neurological disorders.

Anatomical Position and General Structure

The central canal begins inferior to the ventricular system of the brain at the obex, where the fourth ventricle tapers into the spinal cord. Throughout the cervical and thoracic regions, the canal typically lies in the posterior third of the spinal cord, maintaining a narrow calibre. In the lumbar region, it becomes more centrally positioned and may enlarge slightly.
At the conus medullaris, the tapered caudal end of the spinal cord, the canal’s position shifts anteriorly. This region often displays anatomical variation, reflecting the junction between the spinal cord proper and the filum terminale.
The canal functions as a conduit for cerebrospinal fluid (CSF), which it receives from the ventricular system. Its location and continuity with the brain’s ventricles support both mechanical protection of the spinal cord and limited nutrient transport.

Terminal Ventricle

The terminal ventricle—also termed ventriculus terminalis, fifth ventricle, or ampulla caudalis—is the widest portion of the central canal. It is situated at or near the conus medullaris. Anatomically, it represents a fusiform dilation measuring approximately 8–10 mm in length.
Historical descriptions include work by Stilling (1859) and Krause (1875), the latter introducing the term fifth ventricle following his observation of normal ependymal cells within the cavity. The terminal ventricle is typically visible in the fetus and young children, but is usually absent or inconspicuous in adults. In paediatric imaging, it may be identified on MRI or ultrasound, particularly in children under five years of age. Although normally benign, its enlargement can occasionally produce clinical symptoms.

Microanatomical Features

The central canal shares its developmental origin and epithelial characteristics with the cerebral ventricular system. Its lining comprises ciliated columnar ependymal cells, which facilitate CSF movement. Beneath this lies the substantia gelatinosa of Rolando (also known as the substantia gelatinosa centralis), a gelatinous region composed largely of neuroglia with sparse nerve cells and fibres.
The processes of the ependymal cells extend into this gelatinous region, contributing to structural support and maintaining the integrity of the canal’s epithelial boundary. The surrounding grey matter integrates the canal into the central spinal cord architecture, particularly in sensory processing regions.

Developmental Considerations

During embryonic development, the neural tube forms a central lumen that eventually becomes the ventricular system and spinal canal. The central canal thus represents the adult remnant of this embryonic cavity. With advancing age, the canal frequently undergoes occlusion, either partially or completely. These changes, considered part of normal ageing, vary between individuals and do not necessarily produce symptoms.

Functional Role

The central canal plays a modest but important role in circulating cerebrospinal fluid, complementing the broader CSF flow through the ventricles and subarachnoid space. By maintaining continuity with the ventricular system, it assists in distributing nutrients and contributes to the cushioning effect that protects the spinal cord from mechanical forces. Although its functional significance decreases when occlusion occurs, in early life the canal remains patent and physiologically active.

Clinical Significance

Disorders associated with abnormal structure or function of the central canal primarily involve disturbances in CSF flow:

• SyringomyeliaThis condition results from obstruction of the canal, commonly at the lower cervical or upper thoracic spinal levels. Fluid accumulation leads to the formation of a syrinx, which may damage decussating fibres in the anterior white commissure. Clinical consequences often include loss of pain, temperature sensation, and motor function at levels corresponding to the lesion, typically affecting the side opposite the compromised fibres.
• HydromyeliaIn this condition, the central canal becomes dilated due to increased CSF volume. It is closely related to syringomyelia, and in some classifications the terms overlap, as both involve pathological fluid accumulation within or adjacent to the canal.
• Terminal Ventricle AbnormalitiesAlthough usually a developmental variant, an enlarged terminal ventricle may occasionally produce symptoms, particularly in young patients. Detection generally occurs through neuroimaging, and its significance depends on associated findings and clinical presentation.