Etiology: The exact cause for Chiari Malformation is unknown. It has been suggested that malformations happen during the early development of the embryo. Etiopathology is not clear, considering different theories. Historically it has considered them like purely congenital pathologies, but in the last years publications describing a secondary origin are more frequent. There is not a single theory that can explain all the alterations that are expressed clinically, that is why it is more attractive to think about the possibility of a combination of the different theories. In general four possible theories are accepted to explain the congenital forms:

1, Traction’s Theory: in type II the lumbar malformation would perform a traction on the structures of the later grave, originating the reduction of this structures.

2, Alteration of the flow dynamics ‘s Theory: the presence of hydrocefalia would perform a pressure on the cerebellum and trunk in the direction of the flow, resulting in a displacement of these structures through the foramen mágnum.

4. Insufficient development of the later grave: according to this theory, that it seems the most reasonable one, the cerebellum wouldn ‘t be tractioned not pushed, but it would be forced to grow in the direction of the rachidian channel due to the small volume of the later grave. The congenital hernia is developed during the fetal life due to the growth of the cerebellum in a small later grave. At this moment the hernia degree will depend on the asymmetry between continent and content and on the immaturity of the ligaments that allow a greater mobility of the structures, that is a greater dropping of them.

In summary, the existence of a small later grave is due, according to this theory, to a defect in the génesis of the occipital bone or to a too low implantation of the transversal sine. Both alterations are common in-patients with this pathology. A separate chapter represents the cases of malformation of Chiari type I which is acquired. In general it thinks that the leading factor is the creation of a gradient of skull-spinal pressure of L.C.R.. Cases of syringomyelia associated to acquired forms of this pathology have been reported, possibly then, most of these acquired forms would derive in syringomyelia if the necessary time occurred. Sumeer Sathi reported a case in which the cerebelum tonsils’s hernia was observed after repeated lumbar punctions. Once closing the produced dural defect, the reposition of the structures of the later grave could be verified by RMI. In relation to the fisiopathology of this form, the theory of "dissociation of the pressures of skull-spinal LCR" acquires vital importance which would produce a dropping of the cerebelum tonsils.

There are also reported cases associated to rickets resistant to vitamin D and to spontaneous fistulas of LCR.

GENETIC. In some families, there are more than one person with chiari type I and syringomyelia. This phenomenon is known as familial aggregation. The present efforts of the investigation are being centered in establishing that the familial aggregation is due to a genetic cause. They are making MRI studies in all the members of the family, in some of the families who already have more of a patient diagnosed with chiari type I and syringomyelia, including some members of the family that do not have symptoms. This study is been performed at the moment in the USA

It studies carefully each region of each chromosome to find a region that contributes to chiari I and syringomyelia. Then, these regions are studied in detail. The following progression steep is looking for the implied genes. There are hopes that in next years the investigators who work together will be able to explain what changes happen in these chromosomes to cause Chiari type I and syringomyelia.

The chiari malformation is a displacement further down of the cerebellum and, sometimes, of the cerebral trunk, that is located below the foramen magnum (3 mm below this foramen in the examination with a magnetic resonance RM) Several authors agree in indicating that often is associated to bone malformations of the occipito-cervical hinge (small later grave, platibasia, assimilation of C1, Syndrome of short Klippel-Feil and clivus)

The photo shows the anatomical structures involved in the production and flow of the cerebrospinal liquid with the ventricular system, the brain and the spinal marrow, and finally the absorption in the sanguineous circulation. You also will see that the difference between "a normal" cerebellum and the cerebellum of a patient with ACM with the cerebelum tonsils standing out.

Initial symptoms may be light and different. For this reason they are often sent to psycologist or psychiatrists because of the different symptoms so little evident. Most of the symptoms are related to the compression of the lower craneal nerves or the structures of the cerebral trunk

Although it is barely symptomatic, hernias greater to 12 mm are invariably symptomatic, but from those between 5-10 mm, only 30% are symptomatic, there is an association with syringomyelia / hydormyelia that fluctuate rom 20 to 40% until 50 to 75% of all the cases, nevertheless if we only consider the symptomatic patients the presence of syringo-hydromyelia increases to the 60-90% All the symptoms can be intermittent and to improve with the horizontal position. The patients with type I go to medical consult with symptoms originated for some of these causes:

Occípito cervical pain: This is the commonest, symptom, and specially the migraine that generally is referred to the suboccipital region. It can constitute the initial symptom and it is due to the impact of the structures of the later brain in the foramen magnum. Usually it is accentuated with the cough, the movements of the neck and the exercise. Sometimes the pain can be radiated to the arms. As much the cough as the exercise can trigger syncope by the abrupt increase of the intracraneal pressure, therefore it must be considered as an alarm sign.

It is a communication type syringomyelia (or hydromielia). The syndrome can be characterize by parestesias and suspended termoalgésic anesthesia (scalp, neck, shoulders, arms and superior region of the thorax) that can begin in unilateral form and that it is due to an interruption of fibers of termoalgésic sensitivity, It can begin too with an atrophy and motor deficit of muscles of the hand and the arm with abolition of the miotatics reflections (by injury of the second neuron) and signs of commitment of the large tracts (by growth of the intramedular cyst, or by the malformations of the associated occipito-cervical hinge). The sensitive and motor commitment (or periependimario syndrome) acts in the levels that correspond to the medular cyst, and it is the responsible for the frequent presence of scars of burns in these patients. The clinical picture never pulls back spontaneously.

Diplopía, trigeminal neuralgia, sickness, dizziness or paresia are common. The affectation of the cerebral trunk is shown as a horizontal, rotatory or diagonal nystagmus and dissociation of the ocular movements (the patient is conscious of the nistágmic movement of the eyes). It can be experienced a nystagmus limited to the eye where the look is directed (this sign is particularly suggestive of multiple sclerosis and the differentia diagnosis l must be made):

Cerebelum syndrome: It is observed in 11% of the cases . The nystagmus presence is well-known, it is vertical and beats generally downwards, which in some patients produces vertigo when watching towards the floor. Also it can appeared ataxia of trunk and extremities and disartria.

It can be also present: the sign of Lhermitte (sensation of electrical unloading from the nape of the neck to the back or the extremities when the head is bended, present also in the multiple sclerosis), weakness in some member and commitment of the inferior members generally like spasticity.

The most common symptoms in adult are usually developped most frequently at the age of 40’s and in women more often than in men. There are circustancies that may cause the appearence of this symptos before, such as car accidents, give a birth, have neck contractions, etc

Sensations of hummings in the head 58% burning sensations like electrical ones 26%

Arnold Chiri ‘s malformation type I can be confused with an expansive injury or a vascular malformation of the region of the occipital hole or the high part of the cervical marrow. Clinically it can be difficult to differentiate from a multiple sclerosis, and specially when the malformation of the cerebral weave appears in absence of significant bony changes. The ideal method to clarify any of these diagnosis is by RMI.

The treatment is complex. Progressive hydrocefalia requires ventricular derivation. The symptoms and signs of commitment of the structures of the later grave and the high part of the spinal marrow can improve with the suboccipital decompression and superior cervical laminectomy. Within the factors that influence in the postoperating evolution we can mention as negative the presence of atrophy, ataxia and scoliosis in the presurgical examination. Another parameter to consider is the time between the beginning of the symptoms and the surgery, in general better results are observed in patients treated surgically before two years of the beginning of the clinical picture.

Most of the authors recommend the early surgical treatment of this pathology. The surgical treatment of type I (swith a syringomyelia case) is recommendable when the clinic progresses or the RMI demonstrates increase of the growth of the cyst. The asymptomatic patients must be observed and be operated when they begin symptoms. The symptomatic but stable patients per years only must be observed and be operated when deterioration signs increase. The malformation type II only requires surgical treatment when reviewed respiratory symptoms appear. The procedure to follow is the decompression of the posterior grave (that finally it is necessary in the 18,7% from the patients with myelomeningocele), but always considering that it is necessary to place a first shunt of LCR in the patient.

The treatment of syringomyelia associated to type I corresponds to the treatment for Chiari as well as to myelomeningocele and hydrocefalia `s treatment.

The single decompression of the later grave or in combination with other procedures is the surgical technique most used at the moment.

This procedure consists of perfoming an suboccipital craniectomy associated to a laminectomy of the entire cervical vertebra necessary to decompress the tonsils and vermis in all its extension, since the reduction of these nervous structures usually is very important. Other authors like Gregg and col. advise to perform a graft of duramadre and the obliteration of the obex ( with muscle) and a shunt of the fourth ventricle altogether with the decompression of the later grave.

In general, an small sub-occipital craniectomy and a laminectomy of the atlas is performed and, sometimes of C2 too, altogether with the incision of the duramadre and revision of the entrance of the fourth ventricle. If there is some membrane that prevents the exit of the LCR, which is a little frequent finding, it must be perforated.

Since the adhesions can be one of hydromielia reasons, by interruption of the routes of LCR drainage, surgeons has to try to manipulate the cerebelum weave as less as possible, not to stimulate the fibrosis formation.

A concept to consider is that in these patients the implantation of the transversal sine usually is extremely low, so surgeon must be careful during the opening of duramadre. In addition it is advisable not to exaggerate in the size of the occipital resection (3 by 3 cm.) because the compression does not take place in the later grave but in the foramen mágnum and, however, it favors the appearance of hernias in the cerebelum hemispheres.

Some authors put emphasis in not trying to remove the adhesions that maintain the tonsils united to avoid the possible injuries in structures like the P.I.C.A., etc. Nevertheless, others advise to separate them carefully and to produce their retraction by means of bipolar coagulation.

According to the experience of Kazutoshi H. and col. the syringo-subaracnoideo shunt is superior to the decompression of foramen magnum like initial treatment for syringomielia in the Chiari malformation o type I, specially for those patients with great cavities and a fast evolution of the symptoms. With this procedure they obtained a greater neurological improvement (97% against 82%), a greater lightening of the pain and faster closing of the cavity (average time of 1,8 weeks against 6,3 weeks). Kazutoshi also considers like therapeutic possibility the shunt.

The remodelling of the later grave described by And Rubio and col. in 1994 (Vall Hospital d'Hebron, Barcelona) consist of a classic decompression with total conservation of the arachnoid plane. A synthetic graft of duramadre is added and then three surgical points to the superficial muscular plane fix it. This way duramadre appears in carp form, preventing the adhesions and developing an artificial magna cisterna that can be showed in RMI ‘s images. In all the cases displayed in this article the replacement of the tonsils was verified.

When the studies show signs of ventral compression of the encephalic trunk some authors recommend the transoral resection of the odontoid because they maintain that these patients can get worse with a decompression of the later grave. However they obtain a clear improvement in all the cases. Also it seems reasonable to perform this procedure in those patients whose RMI show signs of worsening of the basilar impression after the later decompression. Within the postoperating complications, the respiratory depression is the most frequent, therefore the checking of this function is important. This happens generally in the first 5 days and at night. Other risks are: hernia in the cerebelum hemispheres and vascular injury (P.I.C.A.).

Its surgical treatment correspond to the hydrocefalia (positioning of a by-pass valve of LCR) and myelomeningocele’ s one. Commonly it has been argued that the poor results in the decompression of the later grave of children with this pathology are due to neurological findings produced by intrinsic anomalies of the trunk that this procedure cannot solve. A dissident point of view maintains that the chronic compression of the trunk and isquemia produces histologic injuries, therefore the decompression of the encephalic trunk must be carried out urgently in children with Chiari Type II and suffering the following symptoms: neurogénical disfagia, estridor and apneical pauses. Pollack and col. also maintain that an important component of the malfunction of the trunk is produced by acquired phenomena, therefore suggested decompression must be carried out urgently in those children with Chiari type II and with symptoms of trunk malfunction.. The procedure habitually performed is the decompression of the later grave with the positioning of a patch of duramadre. In the same care than in surgery of type I is required. It is important not to try to dissect the tonsils of the underlying marrow. It is recommendable to perform a traqueostomy, often transitory, in the children who present in the preoperating symptoms of estridor and paralysis of the laryngeal abductor. The control of the breathing in the postoperating period is fundamental due the elevated risk of obstruction and diminution of the respiratory frequency.

The documentation in literature about the evolution of these patients is very confused. The group of patients who will improve and the one who won’t, it is not clearly defined. Rhoton maintains that the greater benefit of the surgery is to delay the advance of the pathology. The morbidity and present operating mortality are very small. In general it is accepted that the symptoms due to compression of the cerebral trunk (specially the cervicocefalalgia) have a good response to the surgery, disappearing in some cases. Also the cerebelum syndrome has a good answer.

According to William Bell and col. children as much as adolescents and adults respond better to the descompression surgery than children younger than one year old, who in general present a little answer. This one could be because the compression within the first year of life can produce isquemic damage in the cerebral trunk or because these children would present a neurological citoarquitecture previously altered. The postsurgical clinical improvement of the muscular weakness is only observed in 16-50 % of the patients. Worse results are observed when there is a muscular atrophy, since rarely some improvement after the surgery has been verified.

In the treatment of the syringomyelia syndrome the patients who do not have important motor deficit and who get operated soon obtain an important improvement; nevertheless symptoms can be left, in special those that affect the hands. In relation to this, Blond and col. (32) achieved a good result with RFP but without finding a statistically significant difference between this technique and the classic decompression of later grave.

With regard to the long tracks, there is an improvement more subjective than objetive defined with the clinical examination. There is no an exact correlation between the clinical evolution and the postoperating images. In some cases of improvement the cyst does not vary its size, on the contrary in some patients can be observed a total collapse of the cavities after the intervention without a clear clinical correlation.

For Pollack and col. the urgent decompression of the children with Chiari type II and symptoms of main trunk malfunction offers very good results. 10 of the 13 children treated with this methodology presentedd a clear and fast improvement of the symptoms after the surgery. 68% obtain a total or nearly total resolution of the symptoms, 12% present as after effects some moderate deficit and a 20% does not present improvement. Respiratory failures are the first cause of death, followed by meningitis/ventriculitis and broncoaspiration).

According to some studies with patients aged between 7 months to 6 years postoperating mortality was of the 37.8%. The preoperating state and the fast deterioration of the symptoms are the more important predictive factors. The paralysis of bilateral vocal cords is a very important and negative predictive factor resulted from the surgery.