**4. Clinical arguments**

Magnetic resonance imaging, if scrutinized really carefully, can provide much more information than just detect Chiari malformation type I. Early on, we mentioned the special meaning that a retroflexed odontoid can get as a proof of caudal traction applied on the occipito-cervical junction (**Figure 2**).

In many Chiari malformation type I patients, we can ascertain a descent not only of the cerebellar tonsils but seemingly of the whole cerebellum, as there is a readily identifiable difference of width of subarachnoid spaces above and behind the cerebellum, a feature that others have labeled "obliteration of retrocerebellar cerebrospinal fluid spaces" [17] following a different interpretation; of course, if a diminished posterior fossa volume were the cause of the tonsillar descent, there would be no free subarachnoid space visible underneath the tentorium as we see in many patients (**Figure 3**).

But maybe the most spectacular image testimony of the mechanisms mentioned above is the feature that we called "tense spinal cord," which has also been described in relation to idiopathic scoliosis [9] but that we could identify in many patients with Chiari malformation type I with or without scoliosis: in sagittal cuts, the spinal cord does not follow closely to the curves of the spinal canal, but instead, it takes the shortest route within the canal and is thus more or less straightened, in some cases even stuck on the concave side of the lordotic or kyphotic curve of the spinal canal (**Figure 4a**), corresponding in axial cuts to an eccentric position of the spinal cord in the canal, closer to the concave side (**Figure 4b**).

We interpret in a similar way another associated image feature, denominated "lateralized spinal cord," visible in coronal or axial cuts (**Figure 5**) and that can be understood as a marker of tension through the spinal cord if one keeps in mind Porter's experimental model [9], this time conditioned by the presence of at least a minimal degree of scoliosis. All this is even easier to figure out by neurosurgeons, because here the spine recalls the principle of functioning of the Leyla retractor system introduced by Gazi Yasargil and so often used to hold brain spatulas. In other words, a central cable in a hollow curved construct will deviate towards the concavity if subjected to axial tension, and in the vertebral column, this can happen either in the sagittal plane, in the coronal plane, or in both.

**253**

**Figure 3.**

**Figure 4.**

*latter towards the* foramen magnum*.*

*Caudal Traction as a Pathogenetic Mechanism of Chiari Malformation Type I*

As an expected consequence of an incomplete understanding of the etiopathogenesis of Chiari malformation type I, its surgical treatment seems the unhappy heir of a mysterious real estate, haunted by dreadful ghosts such as sleep apnea and sudden death. If in some cases it is indeed elementary caution and justified to do no treatment at all, as the tonsillar descent is merely an asymptomatic deformity discovered incidentally, in many other instances, the patients are left to struggle with their own despair as the obvious symptoms and signs they present are not recognized as such by the neurosurgeons in charge. And the reverse is also true: when an active treatment is chosen, it consists usually of suboccipital craniectomy, C1 laminectomy, and duraplasty, which is equivalent to performing an en bloc resection with healthy borders followed by radiotherapy and chemotherapy for a tumor of unknown behavior (not to mention the tonsillar resection added at times). Well, some minimalizing technical advances have been proposed, like leaving the dura mater or the atlas intact, but their problem rests in not getting to the heart of the matter—so, they might lack the desired efficacy. Recent efforts

*Tense spinal cord in a sagittal cut (a) and an axial one (b). The spinal cord travels closer to the concavity of* 

*the curves and occupies an eccentric downward position in axial images (arrows).*

*Increased subarachnoid spaces between the tentorium and the cerebellum reflect the global displacement of the* 

*DOI: http://dx.doi.org/10.5772/intechopen.90044*

*Caudal Traction as a Pathogenetic Mechanism of Chiari Malformation Type I DOI: http://dx.doi.org/10.5772/intechopen.90044*

#### **Figure 3.**

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

traction applied on the occipito-cervical junction (**Figure 2**).

cord in the canal, closer to the concave side (**Figure 4b**).

either in the sagittal plane, in the coronal plane, or in both.

*The causative vector of a retroflexed odontoid is likely parallel to the caudal traction (arrow).*

Magnetic resonance imaging, if scrutinized really carefully, can provide much more information than just detect Chiari malformation type I. Early on, we mentioned the special meaning that a retroflexed odontoid can get as a proof of caudal

In many Chiari malformation type I patients, we can ascertain a descent not only of the cerebellar tonsils but seemingly of the whole cerebellum, as there is a readily identifiable difference of width of subarachnoid spaces above and behind the cerebellum, a feature that others have labeled "obliteration of retrocerebellar cerebrospinal fluid spaces" [17] following a different interpretation; of course, if a diminished posterior fossa volume were the cause of the tonsillar descent, there would be no free subarachnoid space visible underneath the tentorium as we see in

But maybe the most spectacular image testimony of the mechanisms mentioned above is the feature that we called "tense spinal cord," which has also been described in relation to idiopathic scoliosis [9] but that we could identify in many patients with Chiari malformation type I with or without scoliosis: in sagittal cuts, the spinal cord does not follow closely to the curves of the spinal canal, but instead, it takes the shortest route within the canal and is thus more or less straightened, in some cases even stuck on the concave side of the lordotic or kyphotic curve of the spinal canal (**Figure 4a**), corresponding in axial cuts to an eccentric position of the spinal

We interpret in a similar way another associated image feature, denominated "lateralized spinal cord," visible in coronal or axial cuts (**Figure 5**) and that can be understood as a marker of tension through the spinal cord if one keeps in mind Porter's experimental model [9], this time conditioned by the presence of at least a minimal degree of scoliosis. All this is even easier to figure out by neurosurgeons, because here the spine recalls the principle of functioning of the Leyla retractor system introduced by Gazi Yasargil and so often used to hold brain spatulas. In other words, a central cable in a hollow curved construct will deviate towards the concavity if subjected to axial tension, and in the vertebral column, this can happen

**4. Clinical arguments**

many patients (**Figure 3**).

**252**

**Figure 2.**

*Increased subarachnoid spaces between the tentorium and the cerebellum reflect the global displacement of the latter towards the* foramen magnum*.*

### **Figure 4.**

*Tense spinal cord in a sagittal cut (a) and an axial one (b). The spinal cord travels closer to the concavity of the curves and occupies an eccentric downward position in axial images (arrows).*

As an expected consequence of an incomplete understanding of the etiopathogenesis of Chiari malformation type I, its surgical treatment seems the unhappy heir of a mysterious real estate, haunted by dreadful ghosts such as sleep apnea and sudden death. If in some cases it is indeed elementary caution and justified to do no treatment at all, as the tonsillar descent is merely an asymptomatic deformity discovered incidentally, in many other instances, the patients are left to struggle with their own despair as the obvious symptoms and signs they present are not recognized as such by the neurosurgeons in charge. And the reverse is also true: when an active treatment is chosen, it consists usually of suboccipital craniectomy, C1 laminectomy, and duraplasty, which is equivalent to performing an en bloc resection with healthy borders followed by radiotherapy and chemotherapy for a tumor of unknown behavior (not to mention the tonsillar resection added at times). Well, some minimalizing technical advances have been proposed, like leaving the dura mater or the atlas intact, but their problem rests in not getting to the heart of the matter—so, they might lack the desired efficacy. Recent efforts

**Figure 5.** *Lateralized spinal cord deviated towards the left inside the spinal canal.*

complicating more this subject have tried to define instances of cranio-cervical or atlantoaxial instability that supposedly would require complicated and risky procedures applied without firstly securing more confidently a diagnosis of genuine instability—one that is perfectly plausible in selected cases of traumatic spine injury.

Many of the delusions and mishaps issued from the actual therapeutic strategy applied to Chiari malformation type I could be avoided if, taking into account patiently all the facts presented above, one should switch his or her vision from the actual obsession to perform a *circumferential* decompression of the tonsils squeezed against the elongated brainstem to an objective of a rather *longitudinal* or *axial* release of the deformity that affects not only the brainstem-spinal cord junction but the whole of the brainstem *and* the spinal cord starting at the level of the *dorsum sellae*—upper end of the notochordal-influenced growth and somitic division of the mesoderm—until the very tailbone that at earlier stages was the advancing front of axial somatic growth and a possible regulator and intermediate of the coupling between the vertebral and spinal cord growth.

The most logical initial step for interfering with this pathogenesis, considering caudal traction as a final common pathway of multiple etiologies, would be to interrupt this unique route of producing damage to the brain, spinal cord, and spine itself. Technically, this is straightforward if done at the caudal end of the tense spinal cord instead of a frontal attack upon the delicate, impacted cranio-cervical junction. This should consist of a *filum terminale* release by means of the best available technique. A bonus of this approach is that it eliminates the concerns of a possible worsening of a hidden cranio-cervical instability. Its guarantee of success in releasing the conflict between the tonsils, brainstem-spinal cord junction, and occipital foramen stands in the continuous process of spinal growth which produced the progressive lengthening of the cord throughout the intrauterine life and childhood, by adding up collagen and elastin fibers to the complex tridimensional network that conforms the *pia mater* and holds the spinal cord connected mechanically with the vertebral column during its growth and movements. During adulthood, as we have already mentioned, although growth eventually stops, the axial tension is maintained by ongoing processes of degeneration and atrophy which paradoxically, instead of reverting it, will convert the mentioned *neuro-vertebral asynchrony* into a lifelong feature of the human body.

**255**

**Figure 7.**

*(with permission from Wang et al. [25]).*

**Figure 6.**

*as a possible mechanism.*

*Caudal Traction as a Pathogenetic Mechanism of Chiari Malformation Type I*

Of course, the actual surgical approach of suboccipital craniectomy *does* lead to the completion of a similar release of longitudinal spinal tension but at a much higher cost and with much more risk of potential complications; moreover, it might be less efficient, because in the cervical spine, the stronger and more numerous dentate ligaments limit more the stress release than in the lumbar region.

*Preoperative (A–F) and postoperative (G–L, at 3 months) photographs, radiographs, and magnetic resonance images of a 17-year-old male patient with Chiari malformation type I, idiopathic syringomyelia, and severe scoliosis, operated of spinal resection and instrumentation, with marked improvement of his syringomyelia* 

*Preoperative (a) and postoperative (b, at 30 months) magnetic resonance images of a 56-year-old male patient with Chiari malformation type 0, operated of filum terminale sectioning; the improvement of his idiopathic syringomyelia, visible also in a previous control (not shown), is now quite obvious, pointing to caudal traction* 

Interestingly, against all odds, some subtle developments occurred in recent years in the surgical treatment of Chiari malformation type I, proving that more

*DOI: http://dx.doi.org/10.5772/intechopen.90044*

*Caudal Traction as a Pathogenetic Mechanism of Chiari Malformation Type I DOI: http://dx.doi.org/10.5772/intechopen.90044*

### **Figure 6.**

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

complicating more this subject have tried to define instances of cranio-cervical or atlantoaxial instability that supposedly would require complicated and risky procedures applied without firstly securing more confidently a diagnosis of genuine instability—one that is perfectly plausible in selected cases of traumatic

Many of the delusions and mishaps issued from the actual therapeutic strategy

The most logical initial step for interfering with this pathogenesis, considering caudal traction as a final common pathway of multiple etiologies, would be to interrupt this unique route of producing damage to the brain, spinal cord, and spine itself. Technically, this is straightforward if done at the caudal end of the tense spinal cord instead of a frontal attack upon the delicate, impacted cranio-cervical junction. This should consist of a *filum terminale* release by means of the best available technique. A bonus of this approach is that it eliminates the concerns of a possible worsening of a hidden cranio-cervical instability. Its guarantee of success in releasing the conflict between the tonsils, brainstem-spinal cord junction, and occipital foramen stands in the continuous process of spinal growth which produced the progressive lengthening of the cord throughout the intrauterine life and childhood, by adding up collagen and elastin fibers to the complex tridimensional network that conforms the *pia mater* and holds the spinal cord connected mechanically with the vertebral column during its growth and movements. During adulthood, as we have already mentioned, although growth eventually stops, the axial tension is maintained by ongoing processes of degeneration and atrophy which paradoxically, instead of reverting it, will convert the mentioned *neuro-vertebral asynchrony* into a

applied to Chiari malformation type I could be avoided if, taking into account patiently all the facts presented above, one should switch his or her vision from the actual obsession to perform a *circumferential* decompression of the tonsils squeezed against the elongated brainstem to an objective of a rather *longitudinal* or *axial* release of the deformity that affects not only the brainstem-spinal cord junction but the whole of the brainstem *and* the spinal cord starting at the level of the *dorsum sellae*—upper end of the notochordal-influenced growth and somitic division of the mesoderm—until the very tailbone that at earlier stages was the advancing front of axial somatic growth and a possible regulator and intermediate of the coupling

between the vertebral and spinal cord growth.

*Lateralized spinal cord deviated towards the left inside the spinal canal.*

lifelong feature of the human body.

**254**

spine injury.

**Figure 5.**

*Preoperative (a) and postoperative (b, at 30 months) magnetic resonance images of a 56-year-old male patient with Chiari malformation type 0, operated of filum terminale sectioning; the improvement of his idiopathic syringomyelia, visible also in a previous control (not shown), is now quite obvious, pointing to caudal traction as a possible mechanism.*

### **Figure 7.**

*Preoperative (A–F) and postoperative (G–L, at 3 months) photographs, radiographs, and magnetic resonance images of a 17-year-old male patient with Chiari malformation type I, idiopathic syringomyelia, and severe scoliosis, operated of spinal resection and instrumentation, with marked improvement of his syringomyelia (with permission from Wang et al. [25]).*

Of course, the actual surgical approach of suboccipital craniectomy *does* lead to the completion of a similar release of longitudinal spinal tension but at a much higher cost and with much more risk of potential complications; moreover, it might be less efficient, because in the cervical spine, the stronger and more numerous dentate ligaments limit more the stress release than in the lumbar region.

Interestingly, against all odds, some subtle developments occurred in recent years in the surgical treatment of Chiari malformation type I, proving that more

**Figure 8.**

*Preoperative (a) and postoperative (b, at 7 years) magnetic resonance images of a 49-year-old female patient with Chiari malformation type I, operated of* filum terminale *sectioning, with impressive improvement of the tonsillar descent from 17 to 13 mm with respect to McRae's line (measured in the cuts with maximal descent).*

and more clinicians are starting to accept that maybe suboccipital craniectomy is not the only surgical solution to this condition. For this reason, we can present here three "surgical" testimonies in favor of the theory of caudal traction, as follows:


**257**

*Caudal Traction as a Pathogenetic Mechanism of Chiari Malformation Type I*

demonstrating that the hindbrains of these patients were abnormally descended preoperatively and improved their position after the indirect surgery and applied to the other end of the spinal cord [22]. In **Figure 8** we present pre- and postoperative images of one of our cases, with a significant ascent of

In the actual state of knowledge, it is imperative to recognize that the development of the hindbrain and the spinal cord is a complex process regulated by genetic, molecular, mechanical, endocrine, and nervous homeostatic mechanisms that compensate one for another—within certain limits—in case of imbalances and disturbances. Nevertheless, it is exactly this complexity, coupled with the elevated functional requirements that the cranio-cervical junction has to meet, that makes their union so sensitive to various pathogenetic factors and determines malformations among which the one known as Chiari malformation type I is the most common. According to all the arguments presented in this chapter, the final common pathway of these etiopathogenetic aggressions seems to be caudal traction, a complex biological phenomenon that by no means should be reduced to a simple mechanical force of axial pull. There is still much left to discover about the physiologic mechanisms that govern the coupling between the growth of the vertebral column and that of the spinal cord during somatic development, where maybe future research will define the roles played by the pineal gland, the subcommissural organ, and the *filum terminale*, just to cite a few of the possible actors

Miguel Bautista Royo-Salvador, Marco Fiallos-Rivera and Horia Salca\* Institute Chiari and Syringomyelia and Scoliosis of Barcelona, Spain

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: hsalca@institutchiaribcn.com

provided the original work is properly cited.

*DOI: http://dx.doi.org/10.5772/intechopen.90044*

**5. Final remarks and future directions**

eligible for this casting.

**Author details**

the tonsils after the filum terminale release.

demonstrating that the hindbrains of these patients were abnormally descended preoperatively and improved their position after the indirect surgery and applied to the other end of the spinal cord [22]. In **Figure 8** we present pre- and postoperative images of one of our cases, with a significant ascent of the tonsils after the filum terminale release.
