**5. Final remarks and future directions**

*Neurostimulation and Neuromodulation in Contemporary Therapeutic Practice*

*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:

1.In fact, it is suboccipital craniectomy itself that opened these new perspectives when in the hands of some fearless teams [23, 24]; it started to be used for treating patients with syringomyelia without tonsillar descent, with encouraging results, but they did not realize their meaning not even when they discovered that in these children, there were image features suggesting a caudal elongation of the brainstem with displacement of the obex and increased diameter of the *foramen magnum*, as occurs also in Chiari malformation type II [24]. In **Figure 6** we show a similar example from our series of patients, where sectioning the *filum terminale* determined a marked improvement of a cervicothoracic syringomyelia in a case of Chiari malformation type 0.

2.Another ingenious team discovered that if they performed idiopathic scoliosis correction by a technique of posterior vertebral column resection with spine shortening and instrumentation after applying compressive forces, the cerebrospinal fluid flow at the level of the *foramen magnum* improved in patients with Chiari malformation type I and syringomyelia, and in many of them, even the latter diminished in size [25]. Obviously, scoliosis surgery by no means could have accomplished any *circumferential decompression* of the occipital foramen but a release of the tension in the brainstem and tonsils (or, as we

3.Yet the most important testimony came from the hands of a group which operated 318 patients presenting both tethered cord syndromes defined according to very exigent criteria and Chiari malformation type I or low-lying cerebellar tonsils of 0–4 mm descent (that we consider as being also Chiari malformation type I, together with more and more authors [1]), but the technique used was not suboccipital craniectomy, but sectioning of the *filum terminale* by means of an L4 laminectomy. Their results were excellent, both concerning the clinical picture and various morphometric criteria of the posterior fossa contents,

stated above, a welcome *longitudinal decompression*) (**Figure 7**).

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**Figure 8.**

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 eligible for this casting.
