Arnold Chiari I Syndrome

Last update: 25/09/2018, Dr. Miguel B. Royo Salvador, Medical Board number 10389. Neurosurgeon y Neurologist.

What is Arnold Chiari I Syndrome?

Arnold Chiari I or Chiari Syndrome is a condition that was described nearly 100 years ago and in general refers to a condition where there is a downward displacement of the lower portion of the brain. The cerebellar tonsils and the lower part of the cerebellum protrude through the foramen occipitalis into the spinal canal. In malformations like Chiari II and III, there is a downward displacement of the spinal cord because it is held tightly by other spinal malformations such as the myelomeningocele or others. At the time when this classification was made no other associated malformation was observed that would explain the origin of Chiari I malfunction and other causes were suggested, such as, problems with the circulation of cerebrospinal fluid (CSF) or small size of the the posterior fossa where the cerebellum is located.

The research that we have conducted for more than 30 years explains that there exists a traction force acting on the spinal cord in Chiari I Syndrome, due to an undetected malformation: tensed Film Terminale. It causes the same symptoms observed in case of Chiari II and Chiari III malformations and pulls the spinal cord into the vertebral canal.

The spinal cord and the vertebral column both have the same length up to the fifth month of the embryonic life. From this point onwards to the adulthood, the spine grows up to twenty centimeters more than the spinal cord. A ligament called filum terminale lies between the vertebral column and the spinal cord and links these two structures. It has been known for 50 years that in some people this ligament may exert a traction force on the spinal cord in the same way as exerted by myelomeningocele in case of Chiari II and Chiari III Syndromes.


cause of Arnold Chiari

What is the function of the filum terminale?

The filum terminale is the result of the union between the membranes that cover the spinal cord adhered to the bottom of the vertebral canal. From the fifth week of the embryo, these membranes join together with the end of the atrophied spinal cord which would have been the human primitive tail. In adults, the filum terminale doesn’t perform any function.

Treatments for this disease:


Sectioning of the filum terminale (SFT):



1. Eliminates the cause of ACHS.I, SM, SCO, PB, BI, RO, KBS and possibly nocturnal enuresis.

2. Eliminates the risk of sudden death.

3. With the minimally invasive technique, the duration of surgery is of 45 minutes. Few hours of hospitalization. Short postoperative period without any restrictions.

4. Improves the symptoms and stops the evolution of the disease like ACHS.I, SM and SCO of angle less than 40 degrees.

5. Avoids hydrocephali due to the impact of the cerebellar tonsils. (SN).

6. Improves the blood circulation throughout the nervous system (CNS) and thus cognitive faculties. (SN).


1. Minimal wound in the sacrum, with minor discomforts that last few hours.

2. The improvement in spasticity can be mistaken for a decrease in strength.

3. Improved sensitivity can be misunderstood as abnormal sensations.

4. Increased brain irrigation can increase brain activity.


(By means of decompression of the foramen magnum or occipital hole)



1. Eliminates sudden death.

2. Some patients improve.


1. Does not eliminate the cause.

2. 0,7 to 12% of mortality, greater percentage of sudden death.

3. Aggressive and mutilating technique with consequences.

4. Slight improvement.

5. Neurological deficit: Depending on the location of the lesion: Hemiparesia (paralysis of half body) from 0,5 to 2,1%. Visual field alteration from 0,2 to 1,4%. Speech alteration from 0,4 to 1%. Sensation deficit from 0,3% to 1%. Instability (walking difficulty) from 10 to 30%.

6. Post-surgical intra-cerebral hemorrhage, from the surgical bed, epidural or intraparenchymal, causing neurological deficit or worsening of a pre-existent deficit from 0,1 to 5%.

7. Heart attack-Edema, variable depending on the process and the situation until 5%.

8. Profound or cerebral superficial infection from 0,1 to 6,8% with cerebral abscess formation, aseptic-septic meningitis.

9. Hemodynamic alteration from the manipulation of cerebral stem injuries.

10. Gaseous embolism (seated postural patients).

11. Cerebrospinal fluid leakage from 3-14% (Fistula of CSF).

12. Post- surgical hydrocephalus.

13. Pneumocephalus.

14. Tetraparesis (Loss in strength in the 4 limbs) incidentally from the surgical position.


How this explanation is useful for the Chiari I patients?

To begin with, the mere sectioning of this ligament called Filum Terminale stops the traction force subjected to the spinal cord. The lower part of the brain stops moving downward into the upper part of the vertebral canal.




Fig 2.- Simplified sagittal section of the skull and the brain; normal position of the organs on the left. But on the right, the cerebellum protruding downward through the foramen occipitalis as in case of Arnold Chiari Syndrome.


Does the sectioning of the filum terminale makes the brain to move back to its original place?

If the human brain had the plasticity and elasticity of a spring or if it was made of rubber, the cerebellar tonsils and the cerebellum would move back to their original position. However, the brain has formed under a strong traction force. When it is freed from this strain, its recovery depends on its degree of plasticity, which equally depends on the age of the patient, the genes, the duration of time and the intensity of the traction force applied on the lower part of the brain.


Then, what is the use of sectioning this ligament?

The first thing achieved with the sectioning of the filum terminale is the elimination of the main force that steers the disease. Therefore, the progression of the disease is stopped when the cause is supressed. The symptoms of the Chiari I disease are due to the stress suffered by the brain tissue as it moves downward and protrudes into the foramen occipitalis. When the filum terminale is cut, in spite of the fact that the magnetic resonance imaging does not show any apparent change in the position of the protruding part of the brain, the strain of the spinal cord disappears and the pressure inside the foramen occipitalis decreases. Congestion and the lack of blood in the affected area improve and, therefore, the symptoms also improve.


What exactly is the surgical sectioning of the filum terminale?

The surgical sectioning of the filum terminale consists in making a small opening at the sacrum bone, at the end of the spine, without involving any inconveniences that could alter the mechanics of the spine. The Filum terminale ligament is exposed and sectioned with microsurgical techniques, all in just half an hour and it has the added bonus of the required hospitalization of less than a day.



Does the traction force acting on the spinal cord have any effect on the brain?

The traction force of the filum terminale, besides forcing the spine to bend in order to prevent the traction of the spinal cord, also pulls downward the lower part of the brain, the so called cerebellar tonsils, into the foramen occipitalis which connects the skull to the spine. It causes the Arnold Chiari Syndrome, a disease that was described nearly 100 years ago and was of unknown cause up to present.



The surgical sectioning of the filum in case of Arnold Chiari Syndrome makes the downward force disappear which is acting on the cerebellar tonsils. It relieves the suffering of the cerebral tonsils as they do not opress themselves into the foramen occipitalis anymore. The operation improves many symptoms of this disease while the cerebellar tonsils normally do not move upwards because they are deformed and have little elasticity.

Is there any consecuences of cutting this ligament?

The filum terminale is the result of the empty cover of the spine cord at the lower back or lumbosacral region. The covering that separates the spinal cord from the spine at the sacrum and lower back, dura mater, arachnoid mater and pia mater, do not contain spine cord anymore and folds as a fibrous cord which forms the filum terminale; this portion of the spinal cord can be compared to a sock we wear. When we pull taking it half way off our foot: the half that does not contain our foot could be cut without causing any risk to our foot. In the same way, the filum terminale can be cut at any point along its length with no harm.


Does the traction force acting on the the spinal cord have any other effect?

The tension caused by filum terminale besides causing the descent of the brain and death of the central portion of the spinal cord generates a bending stimulus on the spine in order to avoid the tension in the spinal cord and causes a deviation of the spine called scoliosis. The surgical sectioning of the filum terminale eliminates the bending stimulus of the spine and stops progression of the scoliosis..




Does this mean that syringomyelia can also be treated with the same surgical technique as Scoliosis and Chiari I Syndrome?

In a similar way to Scoliosis and Chiari I Syndrome, in the case of syringomyelia the sectioning of the filum terminale stops the disease. The cyst resulting from the necrosis remains the same, but it may disappear when the space surrounding the spinal cord opens spontaneously or does so towards its centre where the ependymal canal is found, which connects the centre of the spinal cord to the brain cavities. This does not mean that the disease is cured, it only means that the cyst has emptied; the disease do persist since still there is a traction force acting on the spinal cord. The symptoms of the disease are caused by the death of cells and the tumor-like effect of the cyst. The sectioning of the filum has three beneficial effects: it stops the death of cells caused by spinal cord traction, it helps the non-functioning but alive neurons to recover, and it diminishes the tumor-like effect of the cyst because it relaxes the spinal cord.


Has this treatment been applied to patients?

Patients suffering from Arnold Chiari I Syndrome with or without idiopathic Syrigomyelia and/or idiopathic Scoliosis have been operated at our center. The evolution of the disease was stopped and improvements in the symptoms have been noted, including some spectacular ones in some cases.


Can you give some examples?

You can find patients cases in the testimonials section: Arnold Chiari I Syndrome.


Images: Before and after the Sectioning of the Filum terminale


Case No. 16453


Case No. 14183
chiari malformation
arnold chiari malformation


Case No. 15704
Arnold Chiari I syndrome


Pathologies and the definitions related to the Filum Disease

For more information on the concept of the Filum Disease, please see:

Involved Diseases





  1. Dr. Miguel B. Royo Salvador (1996), Siringomielia, escoliosis y malformación de Arnold-Chiari idiopáticas, etiología común (PDF). REV NEUROL (Barc); 24 (132): 937-959.
  2. Dr. Miguel B. Royo Salvador (1996), Platibasia, impresión basilar, retroceso odontoideo y kinking del tronco cerebral, etiología común con la siringomielia, escoliosis y malformación de Arnold-Chiari idiopáticas (PDF). REV NEUROL (Barc); 24 (134): 1241-1250
  3. Dr. Miguel B. Royo Salvador (1997), Nuevo tratamiento quirúrgico para la siringomielia, la escoliosis, la malformación de Arnold-Chiari, el kinking del tronco cerebral, el retroceso odontoideo, la impresión basilar y la platibasia idiopáticas (PDF). REV NEUROL; 25 (140): 523-530
  4. M. B. Royo-Salvador, J. Solé-Llenas, J. M. Doménech, and R. González-Adrio, (2005) “Results of the section of the filum terminale in 20 patients with syringomyelia, scoliosis and Chiari malformation“.(PDF). Acta Neurochir (Wien) 147: 515–523.
  5. M. B. Royo-Salvador (1992), “Aportación a la etiología de la siringomielia“, Tesis doctoral (PDF). Universidad Autónoma de Barcelona.
  6. M. B. Royo-Salvador (2014), “Filum System® Bibliography” (PDF).
  7. M. B. Royo-Salvador (2014), “Filum System® Guía Breve”.

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