Contact us

Impacted cerebellar tonsils – Arnold-Chiari 0 – what are they and how can they affect your quality of life?

Published by at 17 November, 2023

Within the field of neurosurgery, an ongoing debate surrounds the diagnosis of Arnold-Chiari Syndrome.

The cerebellar tonsils are an anatomical structure in the lower end of the cerebellum, which have their place in the skull, within the limit of the foramen magnum. When they extend beyond the limit by more than 3-5-7 mm (this value varies depending on the author), and there are no other spinal cord malformations, it is diagnosed as Arnold-Chiari Syndrome type I.

Between 2018 and 2020, some authors introduced a new classification for the types of Arnold-Chiari Syndrome, now including types 0, 1.5, and V.

Within this ongoing discourse, there is a tendency to question whether even a slight descent of the cerebellar tonsils might truly represent a clinical manifestation of Arnold-Chiari, with type 0 being the most contested diagnosis.

In recent literature, some authors report the concept of Arnold-Chiari Syndrome 0 to describe patients who do not have syringomyelia, exhibit minimal tonsillar descent, and display typical Chiari I malformation symptoms and signs such as occipital headaches, posterior cervical pain, and cerebellum-medullary dysfunction. However, there are differing opinions on this classification.

Dr. Royo’s team of specialists confirms that in their case series of patients with Filum Disease, several cases have emerged where the severity of symptoms associated with Chiari malformation does not directly correlate with the extent of tonsillar ectopia. Additionally, they have observed the existence of a clinical presentation similar to Arnold-Chiari I in patients without a clear descent.

In fact, from the perspective of research on Filum Disease as a cause of cerebellar tonsillar descent, the pathologies that can be an expression of Filum Disease in magnetic resonance images include:

any descent of one or both cerebellar tonsils underneath the foramen magnum plane, represented by McRae’s line… We also define as Impaction of Cerebellar Tonsils their contact or intimate closeness with McRae’s line, that we consider to be an incipient form of Descent of the Cerebellar Tonsils, representing the equivalent of what other authors have denominated ‘Chiari malformation type 0’

It would undoubtedly be of great significance for patients if a consensus diagnosis is eventually reached and it is recognized that the condition of impacted cerebellar tonsils within the foramen magnum – which can be observed through magnetic resonance imaging, even when it does not exceed 3 mm – may correspond to a clinical presentation that can impact the patient’s quality of life as much as Arnold-Chiari Syndrome I.

Our Institute provides an effective treatment, the Filum System®, to patients with Arnold-Chiari 0 as well, with excellent results. These results demonstrate that the traction caused by an excessively tense filum terminale can lead to numerous symptoms, even in cases where cerebellar tonsils are only minimally impacted in the foramen magnum. Following our minimally invasive surgical procedure, these symptoms can improve or disappear, thereby restoring a good quality of life for patients.


Opening hours

Monday to Thursday: 9-18h (UTC +1)

Friday: 9-15h (UTC +1)

Saturday and Sunday closed

[email protected]

Care 24 hours

in the form of our website

+34 932 800 836

+34 932 066 406

Legal advice

Legal regulations

Legal notice


Pº Manuel Girona, nº 32

Barcelona, España, CP 08034