Fact-checked by Grok 2 weeks ago

Spinal canal

The spinal canal, also known as the vertebral canal, is a continuous bony cavity formed by the stacked vertebral foramina of the vertebral column, extending from the foramen magnum at the base of the skull to the sacral hiatus at the lower end of the sacrum.^[1] This tubular structure serves as a protective enclosure for the spinal cord, its meninges, cerebrospinal fluid, and associated nerve roots, facilitating the safe transmission of neural signals between the brain and the rest of the body.^[2] Structurally, the spinal canal is delineated by the posterior aspects of the vertebral bodies anteriorly, the pedicles and laminae of the vertebral arches laterally and posteriorly, and the ligamentum flavum connecting adjacent laminae.^[1] Its cross-sectional diameter varies regionally, measuring approximately 17 mm in the cervical spine, narrowing to about 15 mm at the mid-thoracic level (the smallest dimension), and widening again to around 17.5 mm in the lumbar region, which accommodates the broader vertebral bodies and the cauda equina.^[1] The spinal cord itself, a cylindrical extension of the central nervous system, occupies the upper two-thirds of this canal in adults, typically terminating at the conus medullaris between the first and second lumbar vertebrae, beyond which the canal contains the bundle of lumbosacral nerve roots known as the cauda equina.^[3] Enclosed within three protective layers—the dura mater, arachnoid mater, and pia mater—the spinal cord and its contents are further cushioned by cerebrospinal fluid, which circulates through the subarachnoid space.^[3] The spinal canal's design enables the emergence of 31 pairs of spinal nerves through intervertebral foramina, comprising eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal pair, which distribute sensory and motor innervation to the body's periphery.^[2] This anatomical arrangement not only shields the delicate neural elements from trauma but also supports the vertebral column's role in posture and movement, with deviations such as spinal stenosis or herniated discs potentially compressing the canal's contents and leading to neurological deficits.^[1]

Anatomy

Gross anatomy

The spinal canal, also known as the vertebral canal, is the bony cavity within the vertebral column formed by the superposition of the vertebral foramina, extending continuously from the foramen magnum at the base of the skull to the sacral hiatus. This structure provides a protective conduit for the spinal cord along its length.^[1]^[4] The anterior boundary of the spinal canal is defined by the posterior surfaces of the vertebral bodies and intervertebral discs, reinforced by the posterior longitudinal ligament that spans the posterior aspects of these bodies. Posteriorly, the boundary is formed by the vertebral laminae and the ligamenta flava, which are elastic ligaments connecting the laminae of adjacent vertebrae. Laterally, the pedicles of the vertebrae enclose the canal, with the intervertebral foramina providing outlets for spinal nerves. These bony and ligamentous elements collectively create a tubular enclosure that maintains structural integrity throughout the column.^[1]^[4] In adults, the spinal canal measures approximately 57 cm in length on average, accommodating the spinal cord, which terminates around the L1-L2 level. The anteroposterior diameter varies regionally, averaging 15-25 mm, with narrower dimensions in the mid-cervical (around 15-17 mm at C5) and upper thoracic regions, and wider in the lumbar and sacral areas. The epidural space represents the outermost compartment within the spinal canal, lying between the dura mater and the surrounding bony and ligamentous walls.^[5]^[1]^[4]

Regional variations

The spinal canal exhibits distinct regional variations in dimensions and shape to accommodate the differing demands of neural structures and spinal biomechanics across its length. In the cervical region, the canal is the widest, with an average anteroposterior (AP) diameter of approximately 17-20 mm in the upper segments (C1-C3), narrowing slightly to 14-17 mm in the lower cervical levels, reflecting the cervical enlargement of the spinal cord that supports upper limb innervation via the brachial plexus.^[1]^[6] The shape here is typically triangular or oval, providing ample space for the larger cord diameter of up to 13 mm.^[7] In contrast, the thoracic region features the narrowest canal, with AP diameters ranging from 13-18 mm, smallest at mid-thoracic levels like T4 (around 15 mm) and slightly wider at T12 (up to 18 mm), maintaining a relatively uniform circular or oval cross-section to support postural stability and rib articulation.^[1]^[8] This narrower configuration aligns with the smaller thoracic spinal cord diameter of about 6-10 mm and the absence of major enlargements.^[6] The lumbar region shows progressive widening, with AP diameters averaging 15-25 mm and transverse diameters of 26-30 mm, adopting a triangular shape in the lower segments to house the cauda equina nerve roots.^[9]^[7] At L5, the canal reaches up to 17.5 mm AP, facilitating the increased neural volume post-spinal cord termination.^[1] In the sacral region, the canal tapers gradually, maintaining an AP diameter of about 17 mm at S1 before narrowing to fuse into the sacral canal, which ends at the sacral hiatus and contains the terminal filum and sacral nerve roots.^[8] The shape remains triangular, adapting to the fused sacral vertebrae.^[7] These variations are influenced by vertebral morphology, such as the size and orientation of the vertebral foramina, which determine the canal's baseline dimensions; spinal curvatures like cervical lordosis and thoracic kyphosis, which modulate space availability; and age-related changes, including osteophyte formation and ligamentous hypertrophy that can progressively narrow the canal, particularly in narrower thoracic segments, elevating stenosis risk.^[1]^[6]^[7]

Meninges and spaces

The spinal meninges comprise three distinct layers that envelop the spinal cord, providing protection and compartmentalization within the spinal canal: the dura mater, arachnoid mater, and pia mater.^[10] These layers are continuous with the cranial meninges at the foramen magnum and extend inferiorly to enclose the spinal cord and its nerve roots.^[10] The outermost layer, the dura mater, is a robust, fibrous membrane primarily composed of dense collagen fibers, offering tensile strength and mechanical protection to the underlying structures.^[10] In the spinal region, it functions as the sole meningeal layer, as the periosteal component of the dura ends at the foramen magnum, and it continues distally to form the epineurium around spinal nerves.^[10] Its thickness gradually decreases from superior to inferior, becoming thinner toward the coccygeal region.^[10] Lying internal to the dura mater is the arachnoid mater, a thin, avascular, and translucent membrane consisting of flattened fibrocytes connected by delicate collagen strands, which imparts a web-like appearance.^[10] It adheres closely to the dura mater due to cerebrospinal fluid pressure and lacks blood vessels, relying on diffusion for nutrient exchange.^[10]^[11] The innermost pia mater is a delicate, vascularized layer of flattened fibrocytes and collagen bundles that closely invests the spinal cord, conforming to its irregular surface and penetrating its fissures.^[10] It gives rise to lateral extensions known as the denticulate ligaments, which anchor the spinal cord to the dura mater at intervals along its length.^[10] Inferiorly, the pia mater continues as the filum terminale.^[10] Between the arachnoid mater and pia mater lies the subarachnoid space, a fluid-filled compartment spanned by fine arachnoid trabeculae that provide structural support and prevent excessive separation of the meningeal layers.^[10] These trabeculae, resembling a spiderweb, connect the arachnoid to the pia and facilitate the containment of cerebrospinal fluid within this space.^[10]^[11] External to the dura mater is the epidural space, a potential interval between the dural sac and the periosteum lining the vertebral canal, containing adipose tissue, loose connective tissue, internal vertebral venous plexuses, and lymphatics.^[10] This space varies in volume with age and body habitus and holds clinical relevance for epidural anesthesia due to its accessibility for needle insertion.^[10] A narrow subdural space exists as a potential cleft between the dura mater and arachnoid mater, which is normally collapsed and without contents under physiological conditions.^[10] The dural sac terminates at the level of the second sacral vertebra (S2) in adults, below the conus medullaris of the spinal cord.^[12] The filum terminale, originating from the pia mater, extends through the caudal end of the dural sac as the filum terminale externum (coccygeal ligament) to anchor at the dorsum of the coccyx, stabilizing the spinal cord's position.^[12]^[10]

Cerebrospinal fluid and vasculature

The cerebrospinal fluid (CSF) fills the subarachnoid space within the spinal canal, providing a buoyant medium for the enclosed neural structures. This clear, colorless fluid is primarily composed of water (approximately 99%), along with electrolytes such as sodium, chloride, and magnesium at higher concentrations than in plasma, and lower levels of potassium, calcium, and proteins (typically 15-45 mg/dL).^[13] Glucose levels in CSF range from 50-80 mg/dL, and cell counts are normally 0-5 cells/mm³, reflecting its role as an ultrafiltrate of plasma produced mainly by the choroid plexus.^[13] In adults, the total CSF volume is approximately 150 mL, with about 30-70 mL distributed within the spinal subarachnoid space and the remainder in the cranial ventricles and cisterns.^[14] CSF dynamics involve continuous production at a rate of around 500 mL per day, circulation downward through the ventricular system and into the spinal subarachnoid space via the foramina of Magendie and Luschka, and eventual reabsorption primarily through arachnoid granulations into the dural venous sinuses, supplemented by drainage via dural lymphatic vessels to cervical lymph nodes.^[14] Normal CSF pressure, measured during lumbar puncture in the lateral decubitus position, ranges from 7 to 18 cm H₂O, maintaining hydrostatic equilibrium along the neuroaxis.^[13] The vascular elements within the spinal canal include arterial supply to the spinal cord and associated structures, primarily via the anterior spinal artery and paired posterior spinal arteries. The single anterior spinal artery arises from the union of branches from the vertebral arteries and courses along the anterior median fissure, supplying the anterior two-thirds of the cord.^[15] The two posterior spinal arteries originate from the posterior inferior cerebellar arteries (or directly from the vertebral arteries) and descend along the posterolateral sulci, perfusing the posterior one-third of the cord.^[15] These longitudinal arteries receive segmental reinforcement from radicular arteries, which enter at each spinal level via the intervertebral foramina from adjacent spinal arteries; among these, the radiculomedullary arteries serve as critical feeders, with 8-10 such vessels typically contributing significantly to the anterior and posterior systems.^[15] A key radiculomedullary artery is the artery of Adamkiewicz, which arises from the descending aorta (usually on the left) between T9 and L2 levels—most commonly T9-T12—and provides the dominant blood supply to the lower thoracic, lumbar, and sacral segments of the anterior spinal artery.^[15] Venous drainage occurs through an extensive, valveless network of anterior and posterior spinal veins that converge into the internal vertebral venous plexus within the epidural space, which interconnects longitudinally and drains externally via basivertebral veins into segmental veins such as the azygos system in the thoracic region.^[15] This plexus facilitates collateral flow and eventual systemic return.^[16]

Development

Embryological formation

The embryological formation of the spinal canal begins during the third and fourth weeks of gestation, when the notochord induces the overlying ectoderm to thicken into the neural plate, which subsequently folds and fuses to form the neural tube through primary neurulation.^[17] This process starts cranially around day 22 and progresses caudally in a zipper-like manner, completing by the end of week 4, with the neural tube serving as the precursor to the central nervous system, including the spinal cord.^[17] Concurrently, paraxial mesoderm segments into somites along the notochord, with the ventral portions differentiating into sclerotomes that migrate around the neural tube to form the precursors of the vertebrae.^[18] As development proceeds, the lumen of the neural tube, known as the central canal, runs the length of the future spinal cord and becomes continuous with the broader spinal canal space.^[19] The sclerotome cells proliferate and cluster into loosely packed caudal halves and densely packed cranial halves, giving rise to the vertebral bodies and neural arches that enclose the neural tube dorsally by around week 8, thus delineating the bony spinal canal.^[18] The notochord remnants contribute to the nucleus pulposus of intervertebral discs, while sclerotomal cells form the annulus fibrosus, further supporting the structural integrity around the canal.^[18] The meninges, including the dura mater, develop from contributions of neural crest cells and mesoderm by week 8, enveloping the neural tube and establishing the protective subarachnoid space within the spinal canal.^[18] Key milestones include the formation of the foramen magnum by week 6, allowing continuity between the cranial and spinal regions, and the progressive ossification leading to the sacral canal during the fetal period.^[18] By weeks 8 to 10, the spinal cord achieves its definitive segmental form within the maturing canal, with spinal nerves emerging through intervertebral foramina.^[20] Disruptions in these processes can lead to congenital anomalies such as spina bifida, though normal development ensures the canal's enclosure of the spinal cord and meninges.^[17]

Congenital anomalies

Congenital anomalies of the spinal canal encompass structural birth defects that arise from disruptions during early embryonic development, particularly affecting the closure and formation of the neural tube and surrounding vertebral structures. These conditions can lead to incomplete enclosure of the spinal cord, abnormal attachments, or herniations that compromise the canal's integrity and function. While many are detectable prenatally through imaging, their severity varies, influencing neurological outcomes from infancy onward.^[21] Spina bifida represents a primary congenital anomaly characterized by the failure of the neural arch to close completely during fetal development, resulting in defects in the vertebral column and potential exposure or malformation of the spinal cord and meninges. It is classified into several types based on severity: spina bifida occulta, the mildest form, involves a small gap in the vertebral arch without protrusion or neurological involvement, often asymptomatic and discovered incidentally; meningocele features a sac of meninges filled with cerebrospinal fluid protruding through the defect but without neural tissue involvement; and myelomeningocele, the most severe and open form, includes both meninges and spinal cord tissue in the protruding sac, leading to significant nerve damage, paralysis, and hydrocephalus. Recent global estimates (as of 2024) indicate a prevalence of approximately 0.3-0.5 per 1,000 live births, with declines attributed to folic acid supplementation and fortification programs, though rates can reach 1 to 2 per 1,000 in regions with higher folate deficiency among women of reproductive age, underscoring the role of periconceptional folic acid supplementation in prevention.^[22]^[23]^[21]^[24] Tethered cord syndrome occurs due to an abnormal attachment of the spinal cord, typically involving a thickened or shortened filum terminale—the fibrous extension anchoring the cord to the coccyx—which restricts normal upward movement of the conus medullaris during growth, resulting in a low-lying conus position below the L1-L2 vertebral level. This congenital condition, often associated with spinal dysraphism, can cause progressive neurological deficits such as leg weakness, bladder dysfunction, and sensory loss as the child grows, due to mechanical stretching of the cord. It frequently coexists with other anomalies like spina bifida, with diagnosis relying on magnetic resonance imaging to visualize the low conus and filum abnormalities.^[25]^[26] Chiari malformation involves the herniation of cerebellar tissue through the foramen magnum into the upper spinal canal, disrupting the normal flow of cerebrospinal fluid and potentially compressing the brainstem or spinal cord. It is categorized into types based on the extent of herniation and associated features: Type I, the most common, features downward displacement of the cerebellar tonsils without brainstem involvement, often presenting in adolescence or adulthood with headaches and syringomyelia; Type II, typically linked to myelomeningocele, includes herniation of both the cerebellar vermis and brainstem, leading to more severe hydrocephalus and syrinx formation in infancy; and Type III, a rare and severe variant, entails complete or partial herniation of the cerebellum through a posterior skull defect, resulting in encephaloceles and significant neurological impairment. These malformations arise from underdevelopment of the occipital bone and posterior fossa, with Type I prevalence estimated at 0.5-1% in the general population based on autopsy studies.^[27]^[28]

Function

Protective mechanisms

The spinal canal serves as a primary protective enclosure for the spinal cord, formed by the vertebral column, which consists of stacked vertebrae creating a bony tunnel that shields neural elements from external trauma. This bony structure absorbs and distributes mechanical forces across the vertebral bodies and arches, preventing direct impact on the spinal cord during everyday movements or minor injuries. The intervertebral discs, positioned between vertebrae, further enhance this protection by acting as shock absorbers, with their gel-like nuclei distributing compressive loads and maintaining spacing within the canal.^[29] The meninges provide an additional layer of mechanical safeguarding, with the dura mater and arachnoid mater forming tough, fibrous coverings that offer tensile strength to resist deformation and tearing under traumatic forces. The dura mater, the outermost meningeal layer, exhibits high longitudinal stiffness and tensile properties, enabling it to withstand stretching and compression that could otherwise transmit harmful stresses to the underlying spinal cord. Similarly, the arachnoid mater contributes to this barrier function, helping to compartmentalize pressure and limit the propagation of injury forces within the spinal canal.^[30]^[31] Cerebrospinal fluid (CSF) within the subarachnoid space acts as a dynamic shock absorber, providing buoyant support that reduces the effective weight of the spinal cord by approximately 95% and dampens vibrational forces from impacts. This fluid-filled cushioning minimizes direct contact between the spinal cord and surrounding bony or meningeal structures, distributing mechanical stresses evenly and protecting neural tissue from concussive damage. The CSF's viscoelastic properties further aid in dissipating energy during rapid movements, maintaining neural integrity.^[30]^[7] Ligamentous structures enhance overall stability to prevent excessive motion that could compromise the spinal canal's protective environment, with the ligamenta flava playing a key role in limiting vertebral separation and buckling. These elastic ligaments, composed largely of elastin, connect adjacent laminae and resist hyperflexion or extension, thereby preserving the canal's dimensions and avoiding compression of the spinal cord. Other ligaments, such as the denticulate ligaments extending from the pia mater, anchor the spinal cord laterally, providing tensile support to counteract displacement forces during spinal motion.^[32]^[7]

Physiological support

The spinal canal supports spinal cord homeostasis through the circulation of cerebrospinal fluid (CSF) within the subarachnoid space, which bathes the neural tissue and contributes to nutrient delivery and waste removal, supplementing the primary vascular supply. Glucose and oxygen are transported to the spinal cord mainly through blood vessels, with CSF facilitating additional exchange via diffusion driven by arterial pulsations and respiratory movements that propel CSF caudally and cranially along the canal.^[13] This dynamic circulation also facilitates waste removal, as metabolic byproducts and proteins are cleared through bulk flow and the glymphatic pathway, where CSF enters perivascular spaces to mix with interstitial fluid and promote solute efflux, particularly during slow-wave sleep when glymphatic efficiency peaks.^[33] These processes collectively prevent accumulation of neurotoxic substances, sustaining neuronal function throughout the spinal cord.^[34] Epidural fat, distributed along the extradural space of the spinal canal, contributes to physiological stability by providing mechanical buffering and insulation. This adipose tissue cushions the dural sac against compressive forces and facilitates its smooth gliding over the vertebral periosteum during flexion, extension, and rotation, thereby minimizing shear stress on the spinal cord.^[35] Vascular integrity within the spinal canal is upheld by the blood-spinal cord barrier (BSCB), a selective endothelial interface analogous to the blood-brain barrier, which regulates solute exchange to protect neural parenchyma while permitting essential nutrient ingress.^[36] Autoregulation of anterior and posterior spinal artery flow maintains consistent perfusion to the cord, adjusting vascular resistance in response to systemic blood pressure variations between 60 and 150 mmHg to avert ischemia or hyperemia.^[37] The lumbar cistern, a dilated segment of the spinal canal from L1 to S2 devoid of the spinal cord, ensures CSF pressure equilibrium by accommodating fluid volume changes and serving as the primary site for pressure monitoring through lumbar puncture.^[14] This procedure measures opening pressure (typically 70-180 mm H₂O in lateral recumbency) to assess overall CSF dynamics, reflecting the canal's role in balancing intracranial and intraspinal hydraulics.^[38]

Clinical significance

Common disorders

The spinal canal is susceptible to several common disorders that can compromise its structural integrity and neural contents, leading to significant neurological impairment. Among these, spinal stenosis represents a prevalent condition characterized by the narrowing of the spinal canal, which can be congenital or, more commonly, acquired through degenerative processes such as osteoarthritis. This narrowing exerts pressure on the spinal cord or nerve roots, resulting in symptoms like neurogenic claudication—pain, cramping, or weakness in the legs exacerbated by walking and relieved by rest—and, in severe cases, myelopathy manifesting as gait disturbances, urinary incontinence, or upper extremity weakness. Degenerative spinal stenosis affects approximately 8-11% of individuals over 60 years old, with lumbar involvement being most frequent due to age-related disc degeneration and facet joint hypertrophy. Trauma to the spinal canal often arises from fractures or dislocations of the vertebrae, which directly compress the canal and may cause spinal cord injury (SCI). High-energy impacts, such as those from motor vehicle accidents or falls, account for a substantial portion of cases, with cervical and thoracolumbar regions particularly vulnerable due to their biomechanical alignment and the canal's narrower dimensions in these areas. Resulting SCI is classified using the American Spinal Injury Association (ASIA) Impairment Scale, which grades severity from A (complete injury with no sensory or motor function below the level) to E (normal function), guiding prognosis and management. Globally, traumatic SCI incidence ranges from 8 to 55 cases per million population annually, with long-term complications including paralysis and autonomic dysfunction. Tumors within or adjacent to the spinal canal constitute another major category, broadly divided into intradural (within the dura mater) and extradural (outside the dura) types. Intradural tumors, such as meningiomas and schwannomas, are typically benign and slow-growing, originating from arachnoid cells or nerve sheaths, respectively, and often present with radicular pain or sensory deficits due to root compression. Extradural tumors, including metastases from primary cancers like breast or lung, are more aggressive and account for about 70% of spinal tumors in adults, frequently causing cord compression with symptoms of back pain, weakness, and bowel/bladder dysfunction. Overall, spinal tumors represent roughly 10-15% of central nervous system neoplasms, with extradural metastases being the most common subtype in oncology patients. Infections affecting the spinal canal, such as epidural abscess and discitis, pose acute risks through inflammatory compression or direct tissue invasion. Epidural abscesses, often bacterial (e.g., Staphylococcus aureus), form pus collections in the epidural space and can rapidly progress to cord compression, presenting with fever, severe back pain, and neurological deficits like paraplegia if untreated. Discitis involves inflammation of the intervertebral disc, frequently secondary to hematogenous spread, and may extend to involve the canal via osteomyelitis. Risk factors include diabetes mellitus, intravenous drug use, and immunosuppression, with incidence rates estimated at 2-5 cases per 10,000 hospital admissions for spinal infections. Early intervention is critical to prevent permanent deficits, as delays can lead to high morbidity.

Diagnostic approaches

Diagnostic approaches to spinal canal abnormalities rely on a combination of imaging modalities, endoscopic techniques, electrophysiological testing, and standardized clinical scales to identify structural and functional impairments. These methods help detect conditions such as stenosis or compression that may affect the spinal cord, nerve roots, or cerebrospinal fluid dynamics. Imaging plays a central role in evaluation, with magnetic resonance imaging (MRI) established as the gold standard for assessing soft tissues, including the spinal cord and surrounding meninges. T1-weighted sequences provide anatomical detail of the cord and vertebral structures, while T2-weighted sequences highlight cerebrospinal fluid (CSF) as hyperintense, allowing visualization of stenosis through reduced CSF space or altered flow patterns. Computed tomography (CT) excels in delineating bony details, such as osteophytes, facet hypertrophy, or fractures that narrow the canal, offering superior resolution for calcified or osseous abnormalities compared to MRI. When MRI is contraindicated, such as in patients with pacemakers, CT myelography involves intrathecal contrast injection to enhance visualization of the thecal sac, nerve roots, and canal patency, providing dynamic insights into compressions. Endoscopy of the spinal canal, or epiduroscopy, offers direct optical access to the epidural space via a flexible fiberoptic scope inserted through a caudal or interlaminar approach, enabling real-time identification of adhesions, inflammation, or scar tissue in cases of chronic back pain. Electrophysiological assessments, particularly somatosensory evoked potentials (SSEPs), evaluate spinal cord integrity by stimulating peripheral nerves and recording cortical responses, with prolonged latencies indicating conduction deficits due to compression or ischemia. Clinical grading scales, such as the Nurick grade, quantify myelopathy severity on a 0-5 scale based on gait disturbance and ambulatory status, where grade 0 denotes no cord involvement and grade 5 indicates inability to walk, aiding in prognosis and management decisions.

History

Early descriptions

The earliest known references to the spinal canal appear in ancient Greek medical texts, particularly in the context of trauma and vertebral injuries. Hippocrates (c. 460–377 BCE), often regarded as the father of medicine, provided the first descriptions of the vertebral canal in discussions of spinal fractures and dislocations, noting how such injuries could lead to neurological deficits due to compression within the bony enclosure.^[39] He emphasized the canal's role in housing the spinal marrow, linking traumatic deformities like kyphosis to disruptions in this structure, as detailed in his work On Articulations.^[40] Building on Hippocratic ideas, the Roman physician Galen (c. 129–216 CE) advanced anatomical understanding through animal dissections, as human cadaver study was limited. In his extensive writings on anatomy, Galen described the spinal canal as a protective bony tube containing the dural sac, which he identified as the outermost meningeal layer encasing the spinal cord.^[41] He detailed the canal's formation by successive vertebral arches and noted the dura mater's role in safeguarding the neural contents, contributing to early concepts of spinal protection despite inaccuracies from non-human models.^[42] During the Renaissance, renewed interest in direct human dissection led to more precise observations. In 1542, French physician Jean Fernel provided one of the first explicit anatomical descriptions of the spinal canal in his Universa medicina, highlighting its role as a continuous enclosure for the spinal cord and its membranes.^[43] This marked a shift toward systematic physiological terminology.^[44] Shortly thereafter, Andreas Vesalius (1514–1564) offered groundbreaking visual and descriptive insights in his seminal 1543 work De humani corporis fabrica. Through meticulous human dissections, Vesalius illustrated the spinal canal's boundaries, depicting the vertebral foramina forming a protective archway and detailing access methods like transverse sectioning through intervertebral discs to reveal the dural tube and cauda equina.^[45] His woodcut plates provided the first accurate representations of the canal's segmental structure, correcting Galenic errors and establishing a foundational model for modern spinal anatomy.^[46]

Modern advancements

In the early 19th century, François Magendie advanced understanding of the spinal canal's meningeal spaces through his studies on cerebrospinal fluid (CSF) circulation, demonstrating in 1825 that CSF is secreted by the choroid plexuses and flows through the foramen of Magendie into the spinal subarachnoid space, clarifying the fluid dynamics within the canal's protective layers.^[47] Concurrently, the Bell-Magendie law, established in the 1820s by Charles Bell and Magendie, delineated the functional separation of spinal nerve roots—dorsal roots for sensory input and ventral roots for motor output—providing foundational insights into the neural interfaces bordering the spinal canal, though initial credit disputes arose due to Bell's prior observations.^[48] By the mid-19th century, Rudolf Virchow's cellular pathology framework linked degenerative processes to spinal canal narrowing, describing in the 1850s how intervertebral disc protrusions and ligamentous hypertrophy contribute to stenosis by compressing the canal's contents, marking a shift toward histopathological explanations of canal-related disorders.^[49] The 20th century brought diagnostic innovations, with Jean Sicard inventing myelography in 1921 by injecting iodized oil into the subarachnoid space to visualize spinal canal obstructions via radiography, enabling precise localization of tumors and herniations that previously required invasive exploration.^[50] This technique dominated until the 1970s, when magnetic resonance imaging (MRI) emerged, with Paul Lauterbur and Peter Mansfield's developments producing the first clinical spinal images by the late 1970s, revolutionizing non-invasive assessment of canal anatomy, soft tissue pathology, and neural compression without radiation or contrast risks.^[51] Surgical progress accelerated in the 1990s with endoscopic techniques, pioneered by figures like Parvis Kambin, who defined a "safe zone" for transforaminal access in 1990, allowing minimally invasive decompression of the spinal canal for herniated discs and stenosis via small incisions and real-time visualization, reducing recovery times and complication rates compared to open laminectomy.^[52] Into the 21st century, genetic research uncovered links between folate metabolism disruptions and congenital spinal canal anomalies, such as neural tube defects including spina bifida; studies in the 2000s identified variants in genes like MTHFR that impair folate processing, elevating risks by altering neural closure during embryogenesis and emphasizing periconceptional supplementation for prevention.^[53]

References

[1]
Anatomy, Back, Vertebral Canal - StatPearls - NCBI - NIH
The vertebral canal comprises the vertebral foramen located in the cervical, thoracic, and lumbar vertebrae.
[2]
Neuroanatomy, Spine - StatPearls - NCBI Bookshelf - NIH
May 4, 2025 · The spinal cord is housed within the spinal canal, a central lumen within each vertebral body, while spinal nerves emerge at each vertebral ...
[3]
Anatomy and Physiology of the Spinal Cord - NCBI - NIH
The spinal cord is part of the central nervous system (CNS), which extends caudally and is protected by the bony structures of the vertebral column.
[4]
Spinal canal | Radiology Reference Article | Radiopaedia.org
Jul 23, 2025 · The canal consists of a series of vertebral foramina (the holes at the center of the vertebra) linked with discoligamentous structures. Gross ...
[5]
Length relationships between vertebral column and spinal cord - NIH
Jul 2, 2025 · No significant relationship was found between the sex of the subjects or the total SC length and its caudal limit in the vertebral canal. The ...
[6]
Spinal Canal - Musculoskeletal Key
Apr 25, 2020 · Diameter—Internal Surface · Average 20 mm upper cervical, 12 mm lower cervical, · Average 10 mm thoracic, · Average 15 mm in lumbar.
[7]
Spinal Canal - an overview | ScienceDirect Topics
The foramen is small and round in the thoracic, large and triangular in the cervical, lumbar and sacral regions. In the cervical segment, the width of the ...
[8]
Spinal canal | Radiology Reference Article | Radiopaedia.org
Jul 23, 2025 · The narrowest diameter of the spinal canal is at the level of C5, measuring 15 mm, while the widest is at the level of S1, measuring 17 mm. AP ...Missing: regional | Show results with:regional
[9]
Spinal Stenosis: Symptoms, Causes, Treatment
Mar 31, 2022 · According to the norms, the sagittal (anteroposterior) size of the spinal canal at the lumbar level is 15-25 mm, the transverse size is 26-30 mm ...Missing: sacral | Show results with:sacral
[10]
Anatomy, Back, Spinal Meninges - StatPearls - NCBI Bookshelf - NIH
The spinal meninges specifically enclose the spinal cord and stretch from the brainstem down to the filum terminale.
[11]
Lab 2 Spinal Meninges
Three layers of meninges envelop the spinal cord and the roots of spinal nerves. The most superficial menix is dura mater. It is protective by virtue of its ...
[12]
Spinal Cord and Spinal Nerve (3 of 14) - Module
As we said, the dural sac ends at the level of the second sacral vertebra (S2). Caudal to the end of the dural sac is a specialization of meninges called ...
[13]
Physiology, Cerebral Spinal Fluid - StatPearls - NCBI Bookshelf
Aug 9, 2025 · CSF is continuously secreted with a stable and tightly regulated composition, preserving homeostasis within the intracranial environment.
[14]
Neuroanatomy, Cerebrospinal Fluid - StatPearls - NCBI Bookshelf
Jul 7, 2025 · Normal CSF pressure ranges from 8 to 15 mm Hg in the supine position, reflecting the tightly regulated balance between CSF production and ...
[15]
Anatomy, Back, Vertebral Canal Blood Supply - StatPearls - NCBI
The function of the spinal canal and vertebral column is to protect the spinal cord and provide support to the body. It includes foramen such that blood supply ...
[16]
Neuroanatomy, Spinal Cord Veins - StatPearls - NCBI Bookshelf
Jul 24, 2023 · The spinal venous system consists of a network of valveless veins grouped into three intercommunicating drainage systems that empty into extra spinal veins.
[17]
Embryology, Neural Tube - StatPearls - NCBI Bookshelf - NIH
It starts during the 3rd and 4th week of gestation. This process is called primary neurulation, and it begins with an open neural plate, then ends with the ...Introduction · Development · Cellular · Molecular Level
[18]
Embryology, Vertebral Column Development - StatPearls - NCBI - NIH
The embryological development of the vertebrae is complex, but it is vital to understand as errors in development can result in many congenital abnormalities.
[19]
Development of the Central Nervous System - Spinal Cord - TeachMeAnatomy
### Summary of Neural Tube Formation and Related Processes
[20]
22.5 Development of the spinal cord - embryology.ch
From the 8th to the 10th weeks the spinal cord reaches its definitive form. It becomes surrounded by cerebral-spinal cord membranes (meninges) and lie in the ...<|control11|><|separator|>
[21]
Spina Bifida - StatPearls - NCBI Bookshelf
... folic acid fortification had not been introduced into standard prenatal care.[9] The global reported prevalence is 0.5 to 1 per 1000 live births, with 2 ...
[22]
Spina Bifida | National Institute of Neurological Disorders and Stroke
Apr 7, 2025 · There are four types of spina bifida: occulta, closed neural tube defects, meningocele, and myelomeningocele. The symptoms of spina bifida are ...What is spina bifida? · Types of spina bifida · How is spina bifida diagnosed...
[23]
Spina bifida - Symptoms and causes - Mayo Clinic
Dec 19, 2023 · Spina bifida is a condition that occurs when the spine and spinal cord don't form properly. It's a type of neural tube defect.Missing: sources | Show results with:sources
[24]
Neuroanatomy, Conus Medullaris - StatPearls - NCBI Bookshelf - NIH
Tethered cord syndrome is a condition caused by an abnormal filum terminale ... abnormally stretched, with neurologic symptoms referable to the lower cord ...
[25]
Tethered Cord Syndrome - Symptoms, Causes, Treatment | NORD
Various congenital anomalies, particularly spina bifida, are often associated with congenital tethered cord syndrome. Spina bifida is a birth defect due to ...
[26]
Chiari Malformations | National Institute of Neurological Disorders ...
Jul 19, 2024 · Chiari malformations (CM) are caused by problems in the structure of the brain and skull. In Chiari malformations, the lower part of the brain presses on and ...Missing: sources | Show results with:sources
[27]
Chiari malformation - Symptoms and causes - Mayo Clinic
Oct 20, 2023 · Chiari malformation (kee-AH-ree mal-for-MAY-shun) is a condition in which brain tissue extends into the spinal canal.Missing: reliable | Show results with:reliable
[28]
Spinal Cord: Anatomy, Function & Structure - Cleveland Clinic
Your spinal cord is a cylinder-shaped tube of tissue that runs through the center of your spine, from your brainstem to your lower back. It's made of nerves and ...Missing: dimensions | Show results with:dimensions<|control11|><|separator|>
[29]
Neuroanatomy, Spinal Cord - StatPearls - NCBI Bookshelf
Three meninges surround the spinal cord. From outside inwards, they are the dura mater (thick fibrous membrane), the arachnoid mater, and the pia mater. The ...
[30]
Spinal Meninges and Their Role in Spinal Cord Injury
This gives the dura a greater longitudinal tensile strength and stiffness compared with transverse strength. Due to viscoelastic properties of elastin fibers, ...
[31]
Ligamentum flavum - Physiopedia
It resists excessive separation of the adjacent vertebral lamina and prevents buckling of the ligament into the spinal canal during extension, preventing canal ...
[32]
The Glymphatic System: A Novel Component of Fundamental ...
The glymphatic system enables bulk movement of CSF from the subarachnoid space along periarterial spaces, where it mixes with interstitial fluid within the ...
[33]
Mechanisms of fluid movement into, through and out of the brain
Dec 2, 2014 · CSF is also important in removing protein and other debris during recovery from injury or microhemorrhage. It may also serve as a route for ...
[34]
Comparative morphology of fat in the epidural space - PubMed
Comparative morphology of fat in the epidural space. Am J Anat. 1959 Sep:105:219-32. doi: 10.1002/aja.1001050204. Author. H J RAMSEY.
[35]
[PDF] mri diagnosis of spinal epidural lipomatosis - LSMU CRIS
Apr 6, 2017 · Thermal and mechanical protection is offered by the epidural fat. It protects the spinal cord within the dural sac and spinal nerves by ...
[36]
The neurovascular unit in healthy and injured spinal cord - PMC
Autoregulation and neurovascular coupling ensure regional blood flow meets the metabolic demand according to the blood supply or local neural activation. The ...
[37]
Perturbed and spontaneous regional cerebral blood flow responses ...
This study aimed to examine 1) the acute regional CBF responses to rapid changes in blood pressure (BP) during orthostatic stress in individuals with SCI and ...
[38]
Diagnostic Lumbar Puncture - PMC - PubMed Central
We review the technique of diagnostic Lumbar Puncture including anatomy, needle selection, needle insertion, measurement of opening pressure, Cerebrospinal ...
[39]
History of Spine Biomechanics - Clinical Gate
Apr 2, 2015 · Hippocrates was the first to relate traumatic spinal deformities ... In addition, he was the first to describe the spinal canal which ...Classical Antiquity · Scientific Period · Renaissance And Premodern...
[40]
Historical overview of spinal deformities in ancient Greece - PMC
Hippocrates describes the pathology of post-traumatic kyphosis, commonly caused by falling on the shoulder or buttock in his book On Articulations and explains ...
[41]
History of spinal cord localization
Jan 5, 2004 · Galen described the protective coverings of the spinal cord: the bone, posterior longitudinal ligament, dura mater, and pia mater. He gave a ...
[42]
Galen: a pioneer of spine research - PubMed
Galen established a pioneer model for the study of human spine. His research ended in an accurate description of the vertebral column and the spinal cord.Missing: dural tube
[43]
Jean Fernel | Encyclopedia.com
Fernel's anatomical observations, among them the earliest description of the spinal canal, were good and clearly presented, before or simultaneous with ...Missing: medullaris | Show results with:medullaris
[44]
Eyewitness accounts of the 1510 influenza pandemic in Europe - NIH
Jean Fernel (1497–1558) Physician to French King Henri III, physiologist, mathematician, and astronomer who described the spinal canal and lunar craters. He ...
[45]
spine anatomy from the medieval age to the end of the 19th century ...
Oct 11, 2024 · The discovery of spine anatomy followed a problem/solution pattern; it took almost 1000 years to transition from nihilism to perfectionism.
[46]
Historical Anatomies on the Web: Andreas Vesalius Home
Andreas Vesalius' De corporis humani fabrica libri septem, featuring Vesalius performing a dissection in a crowded anatomical theatre.Missing: canal | Show results with:canal
[47]
Magendie and Luschka: Holes in the 4th ventricle - PMC - NIH
Among his numerous studies, those on the CSF were impressive, the first of which was published in 1825. In his book "Physiological dissertation on the ...
[48]
François Magendie (1783–1855) and his contributions to the ...
Olmsted concluded that the designation “Bell-Magendie law” represented a compromise between the points of view of the older anatomist (Bell) who arrived at ...Missing: canal | Show results with:canal
[49]
Lumbar Spine Syndromes - Evaluation and Treatment
In the 1850's Virchow and Luschka described the protruded interverte- bral disc. Luschka's illustrations of a prolapse of the intervertebral disc would be ...
[50]
The History behind the Discovery of Root Tension Signs and ... - NIH
The only imaging study available was Lipidol myelography which was introduced by Sicard and Forestier in 1928 [19]. Hence, it was understandable why surgeons ...
[51]
Neuroradiology Back to the Future: Spine Imaging - PMC
Spinal MR imaging research aimed at acquiring images faster with better contrast and spatial resolution. This led to developments such as fast spin-echo and ...
[52]
A brief history of endoscopic spine surgery
In 1990, Parvis Kambin described a triangular safe zone bordered by the exiting root anteriorly, the travers- ing root medially, and the superior endplate of ...
[53]
Neural tube defects between folate metabolism and genetics - PMC
Neural tube defects (NTDs) are the second most common severely disabling human congenital defects. Worldwide, NTDs incidence is approximately one per 1000 live ...