Abnormality of the Central Canal of the Spinal Cord in Syringomyelia in a Patient With a Basal Skull Malformation (SYRCANAL)

Chiari Malformation Type I (CM-I) is a congenital anomaly characterized by downward displacement of the cerebellar tonsils through the foramen magnum, which may disrupt cerebrospinal fluid (CSF) circulation at the craniovertebral junction. The condition generally results from underdevelopment of the posterior cranial fossa, leading to insufficient space for the cerebellum. This anatomical abnormality can cause a wide range of heterogeneous symptoms, including occipital headaches triggered by coughing or exertion, neck pain, dizziness, balance disturbances, paresthesia, limb weakness, and swallowing difficulties.

One of the most concerning complications is syringomyelia/hydromyelia, which corresponds to the development of fluid-filled cavities within the spinal cord. These cavities may either be adjacent to the central canal (syringomyelia) or result from dilation of the central canal itself (hydromyelia). Associated spinal cord involvement may lead to specific neurological symptoms and is often a major indication for surgical treatment of Chiari malformation.

The decision to perform surgical decompression of the craniovertebral junction must balance the potential benefits against the associated risks. Furthermore, surgical outcomes remain variable and sometimes uncertain. Some symptoms may persist despite surgery, and syringomyelia regression is inconsistent. A better understanding of the pathophysiology of syringomyelia associated with Chiari malformation is therefore essential to improve patient selection and optimize surgical strategies.

Although the pathophysiology of syringomyelia in Chiari malformation has been investigated in several studies, it remains only partially understood. Recently, the position of the obex has been suggested to be associated with the presence of syringomyelia in patients with Chiari malformation. The obex is the neurological structure located at the cranial end of the central canal. Based on previous findings, investigators hypothesize that a low-lying obex may induce deformation of the central canal, creating a folding or kinking effect that could explain downstream canal dilation. Our primary hypothesis is therefore that the morphology of the central canal at the cervicomedullary junction (including angulation, folding, or compression) is a key factor influencing the presence or absence of associated hydromyelia/syringomyelia and, consequently, clinical severity.

Animal studies support a pathophysiological cascade involving initial mechanical deformation of the central canal followed by pericanal inflammation contributing to syringomyelia formation. According to this novel hypothesis, cerebellar tonsillar descent without associated central canal deformation would confer a lower risk of syringomyelia and unfavorable clinical progression than cases involving deformation of the cranial portion of the central canal.

In vivo visualization and morphological assessment of the cranial portion of the ependymal central canal using MRI therefore offer the potential to identify new risk markers for Chiari malformation that may ultimately assist surgical decision-making. However, when the canal is not dilated, visualization remains challenging, as does the identification of potential pericanal inflammation.

Several years ago, Tourdias et al. developed a specific MRI sequence known as White Matter-nulled (WMn) MPRAGE, which enhances contrast between structures of the central nervous system, including the thalamus, thereby improving the accuracy of thalamic assessment in pathological conditions. More recently, this group demonstrated that the WMn-MPRAGE sequence can be adapted for spinal cord imaging, maximizing the detection of spinal cord lesions. In collaboration with the Anatomy Laboratory of the University of Bordeaux, it was demonstrated that WMn-MPRAGE enables reliable visualization of the spinal cord central canal in healthy subjects when compared with previous anatomical specimen studies. Furthermore, recent advances in spinal cord diffusion MRI, particularly through artificial intelligence-based denoising methods, now enable detailed assessment of spinal cord microstructure and may allow quantification of biomarkers associated with pericanal inflammation.

Thus, the pathophysiology of Chiari Malformation Type I remains incompletely understood. Investigators hypothesize that analysis of the morphology of the cranial portion of the ependymal central canal using WMn-MPRAGE imaging, combined with assessment of the adjacent spinal cord microstructure, may provide novel biomarkers of associated syringomyelia risk and clinical severity.