The Human Central Canal of the Spinal Cord: A Comprehensive Review of its Anatomy, Embryology, Molecular Development, Variants, and Pathology

Upper end of the central canal of the human spinal cord: Quantitative anatomical study and 3D modeling

The upper end of the central canal of the human spinal cord has been repeatedly implicated in the pathogenesis of various diseases, yet its precise normal position in the medulla oblongata and upper cervical spinal cord remains unclear. The purpose of this study is to describe the anatomy of the upper end of the central canal with quantitative measurements and a three-dimensional (3D) model. Seven formalin-embalmed human brainstems were included, and the central canal was identified in serial axial histological sections using epithelial membrane antigen antibody staining. Measurements included the distances between the central canal (CC) and the anterior medullary fissure (AMF) and the posterior medullary sulcus (PMS). The surface and perimeter of the CC and the spinal cord were calculated, and its anterior-posterior and maximum lateral lengths were measured for 3D modeling. The upper end of the CC was identified in six specimens, extending from the apertura canalis centralis (ACC) to its final position in the cervical cord. Positioned on the midline, it reaches its final location approximately 15 mm below the obex. No specimen showed canal dilatation, focal stenosis, or evidence of syringomyelia. At 21 mm under the ACC in the cervical cord, the median distance from the CC to the AMF was 3.14 (2.54-3.15) mm and from the CC to the PMS was 5.19 (4.52-5.43) mm, with a progressive shift from the posterior limit to the anterior third of the cervical spinal cord. The median area of the CC was consistently less than 0.1 mm2. The upper end of the CC originates at the ACC, in the posterior part of the MO, and reaches its normal position in the anterior third of the cervical spinal cord less than 2 cm below the obex. Establishing the normal position of the upper end of this canal is crucial for understanding its possible involvement in cranio-cervical junction pathologies.

Persistence of FoxJ1+ Pax6+ Sox2+ ependymal cells throughout life in the human spinal cord

Ependymal cells lining the central canal of the spinal cord play a crucial role in providing a physical barrier and in the circulation of cerebrospinal fluid. These cells express the FOXJ1 and SOX2 transcription factors in mice and are derived from various neural tube populations, including embryonic roof and floor plate cells. They exhibit a dorsal-ventral expression pattern of spinal cord developmental transcription factors (such as MSX1, PAX6, ARX, and FOXA2), resembling an embryonic-like organization. Although this ependymal region is present in young humans, it appears to be lost with age. To re-examine this issue, we collected 17 fresh spinal cords from organ donors aged 37-83 years and performed immunohistochemistry on lightly fixed tissues. We observed cells expressing FOXJ1 in the central region in all cases, which co-expressed SOX2 and PAX6 as well as RFX2 and ARL13B, two proteins involved in ciliogenesis and cilia-mediated sonic hedgehog signaling, respectively. Half of the cases exhibited a lumen and some presented portions of the spinal cord with closed and open central canals. Co-staining of FOXJ1 with other neurodevelopmental transcription factors (ARX, FOXA2, MSX1) and NESTIN revealed heterogeneity of the ependymal cells. Interestingly, three donors aged > 75 years exhibited a fetal-like regionalization of neurodevelopmental transcription factors, with dorsal and ventral ependymal cells expressing MSX1, ARX, and FOXA2. These results provide new evidence for the persistence of ependymal cells expressing neurodevelopmental genes throughout human life and highlight the importance of further investigation of these cells.

Older adult-onset Alexander disease with atypical clinicoradiological features: a case report

Alexander disease (AxD) is a rare autosomal dominant astrogliopathy caused by mutations in the gene encoding for glial fibrillary acidic protein. AxD is divided into two clinical subtypes: type I and type II AxD. Type II AxD usually manifests bulbospinal symptoms and occurs in the second decade of life or later, and its radiologic features include tadpole-like appearance of the brainstem, ventricular garlands, and pial signal changes along the brainstem. Recently, eye-spot signs in the anterior medulla oblongata (MO) have been reported in patients with elderly-onset AxD. In this case, an 82-year-old woman presented with mild gait disturbance and urinary incontinence without bulbar symptoms. The patient died 3 years after symptom onset as a result of rapid neurological deterioration after a minor head injury. MRI showed signal abnormalities resembling angel wings in the middle portion of the MO along with hydromyelia of the cervicomedullary junction. Herein, we report the case of this patient with older adult-onset AxD with an atypical clinical course and distinctive MRI findings.

The immune microenvironment and tissue engineering strategies for spinal cord regeneration

Regeneration of neural tissue is limited following spinal cord injury (SCI). Successful regeneration of injured nerves requires the intrinsic regenerative capability of the neurons and a suitable microenvironment. However, the local microenvironment is damaged, including insufficient intraneural vascularization, prolonged immune responses, overactive immune responses, dysregulated bioenergetic metabolism and terminated bioelectrical conduction. Among them, the immune microenvironment formed by immune cells and cytokines plays a dual role in inflammation and regeneration. Few studies have focused on the role of the immune microenvironment in spinal cord regeneration. Here, we summarize those findings involving various immune cells (neutrophils, monocytes, microglia and T lymphocytes) after SCI. The pathological changes that occur in the local microenvironment and the function of immune cells are described. We also summarize and discuss the current strategies for treating SCI with tissue-engineered biomaterials from the perspective of the immune microenvironment.

Congenital spine deformities: timing of insult during development of the spine in utero

The development of the spine and spinal cord occurs at the earliest weeks of gestation. Their development not only affects each other but also are most likely associated with anomalies in other systems. It is essential to recognize the stages of spine development to understand the cause of congenital spinal deformities and their influences on the postnatal growing spine. A vast majority of congenital spinal problems are not evident clinically. For instance, the presence of neural axis abnormalities, such as spinal dysraphism or syringomyelia, may be so subtle that patients never seek medical care. Certain vertebral formation disorders such as hemivertebrae may remain asymptomatic throughout life if they are balanced while those with congenital bars may develop severe deformity. Major defects in the spine are often associated with abnormalities of the other organs such as cardiovascular and genital urinary system that warrants close attention by multidisciplinary specialists. A thorough understanding of the basics of embryology, which serves as a window into the development of the spine, is necessary to enable the practitioner to appreciate why, when, and where the numerous spine deformities develop in utero. Besides, certain developmental defects manifest in adulthood including spondylolysis, degenerative disc disease, congenital spinal stenosis, and even tumors like cordoma. Thus, understanding embryology can assist to establish the proper diagnosis and ensure optimal treatment.

Soft-bodied adaptive multimodal locomotion strategies in fluid-filled confined spaces

Soft-bodied locomotion in fluid-filled confined spaces is critical for future wireless medical robots operating inside vessels, tubes, channels, and cavities of the human body, which are filled with stagnant or flowing biological fluids. However, the active soft-bodied locomotion is challenging to achieve when the robot size is comparable with the cross-sectional dimension of these confined spaces. Here, we propose various control and performance enhancement strategies to let the sheet-shaped soft millirobots achieve multimodal locomotion, including rolling, undulatory crawling, undulatory swimming, and helical surface crawling depending on different fluid-filled confined environments. With these locomotion modes, the sheet-shaped soft robot can navigate through straight or bent gaps with varying sizes, tortuous channels, and tubes with a flowing fluid inside. Such soft robot design along with its control and performance enhancement strategies are promising to be applied in future wireless soft medical robots inside various fluid-filled tight regions of the human body.

Clearance of cerebrospinal fluid from the sacral spine through lymphatic vessels

Using a tracer-based approach with near-infrared fluorescence and magnetic resonance imaging in mice, the authors establish the concept of a cranial-to-caudal circulation of cerebrospinal fluid within the spinal column, with clearance to lymphatic vessels at the sacral terminus.

The pathways of circulation and clearance of cerebrospinal fluid (CSF) in the spine have yet to be elucidated. We have recently shown with dynamic in vivo imaging that routes of outflow of CSF in mice occur along cranial nerves to extracranial lymphatic vessels. Here, we use near-infrared and magnetic resonance imaging to demonstrate the flow of CSF tracers within the spinal column and reveal the major spinal pathways for outflow to lymphatic vessels in mice. We found that after intraventricular injection, a spread of CSF tracers occurs within both the central canal and the spinal subarachnoid space toward the caudal end of the spine. Outflow of CSF tracers from the spinal subarachnoid space occurred predominantly from intravertebral regions of the sacral spine to lymphatic vessels, leading to sacral and iliac LNs. Clearance of CSF from the spine to lymphatic vessels may have significance for many conditions, including multiple sclerosis and spinal cord injury.