September: Chiari Awareness Month
Clearing Up Doubts
about Type I Syndrome and the Filum System^® approach

Published by ICSEB at 28 September, 2025

As every year, throughout September we are dedicated to raising awareness about Arnold-Chiari Syndrome. On 28 September, the International Day of Arnold-Chiari Syndrome is observed, with the aim of giving visibility to this condition and offering support to those affected and their families.

As is well known, our Institute offers patients a unique approach to treating this condition through our exclusive minimally invasive surgical technique. This method subsequently restores the lesions and functions of the affected nervous system – those which are reversible and can be recovered – with rehabilitation and medication.

Dr Royo’s aetiological finding is that a ligament, the Filum terminale, can be congenitally too tense. This excessive tension causes traction on the entire central nervous system (CNS). Together, these factors constitutes the Filum Disease (FD). One of its consequences, among others, is the descent of the entire CNS including its lower, more visible part – the cerebellar tonsils – through the foramen magnum. This descent is typical of the syndrome.

Currently, Filum Disease is often confused especially with tethered cord, whether occult or not (OTC and TC), which are two types of dysraphism. In the context of this awareness, we would like to take the opportunity to clarify this distinction.

Although the term dysraphism refers to a group of congenital defects that result from  a failure in the closure of the neural tube during embryonic development, Filum Disease can, in some way, be placed within this category. However, Filum Disease in particular consists of a mechanical conflict between the neuro-axis and the spine, which arises when, during the embryonic development phase, they grow asynchronously beyond what is normal.

We believe that this asynchronous growth, together with the aforementioned mechanical conflict, is produced by an apparently normal filum terminale. This is responsible for several conditions, the most frequent one – according to our studies and our databases – being Arnold-Chiari Syndrome Type I. It is provoked by caudal traction, which pulls the entire CNS downwards.

Unlike TC and OTC, in which the Filum Terminale may tether the cord at different levels and in a visible manner on MRI scans, which are different entities from Arnold-Chiari I is a different entity, since there is no evidence of any cord tethering. In contrast, the paradigm underlying the definition of Filum Disease helps explain the descent of the tonsils on its own, as two entities that are closely linked: the first being the cause, and the second its consequence.

This opens new frontiers in research and broadens the treatment options available to patients. It offers them the possibility of a method that addresses the cause rather than the consequence of the condition, with low surgical risk.

By eliminating the cause, the CNS is no longer subjected to constant caudal traction. This gives it the possibility to repair and restore the damage that developed before treatment, leading to an improvement in quality of life in most cases.

Sharing this and other findings from our team helps to raise greater awareness of Arnold-Chiari I Syndrome and to bring hope to patients and their families. We encourage you to take part!

You can find all the relevant information here:
https://institutchiaribcn.com/en/dr-royo-publications/
https://institutchiaribcn.com/en/faq-icseb-en/
https://institutchiaribcn.com/en/diseases-we-treat/arnold-chiari-syndrome/