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Arnold Chiari`s friends
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Syringomielia
Introduction.
In Greek mythology there is the history of God Pan, who used to pursue a nymph called Siringa. Trying to escape, she ran to his father , Rio Ladron, who, to protect his daughter turned her into canes of different sizes. Feeling deceived, the God Pan took seven different canes and turned them into a musical instrument that was called Panflauta or Siringa (Syrinx). Syringomielia means marrow in cane form or flute..
The syringomielia is a pathological condition with several forms. Sometimes the cavity is a central channel expansion in the spinal cord. This is called Hydromielia and has an ependimarial cell coating. Other times the cavity is neighbor to this central channel and it does not have the above-mentioned coating. In these cases the cavity can be or not communicated to the central channel.
The cyst cavity can spread out of the spinal cord including the encephalic trunk: syringobulbia.
Anatomical variety: The central channel normally presents several changes across the years; gradually it becomes narrower in the thoracic region. Changes happen in the epéndima, such as cellular damage, scar healing, small rose spots, acúmulos subependimarios gliovasculares and cellular disorganization.
Besides there is an epithelial change depending on the patient age that consists of the step of epithelium ciliate pseudostratified of the first decade of the life to epithelium colonnade and cuboideo about the second decade. Astrocitos and epéndima cells proliferate after 20 years leading to the occlusion of the central channel. In newborn children and in-children younger than one year old, can appreciate the central channel still opened in the enlarged part of the lumbar spinal cord, through the magnetic resonance.
The syringomielia is always pathological, though it can be asymtomatic and not to need therapy but observation.
Classification:
There exist multiple and different ways of classifying the syringomielia, based principally on its origins or on its production mechanisms. A practical way of classification divides it in seven groups:
Communicating Syringomielia: It consists of the communication of the cyst cavity with the fourth ventricle. It fits to 10 % of the syringomielias.
Not communicating Syringomielia: It is the most frequent, including approximately 50 %. There is no communication with the fourth ventricle and there is a blockade to the traffic of the cerebro spinal fluid from posterior cranial base.
Syringomielia associated to spinal disrafia
Syringomielia associated with internal spinal cord tumors
Syringomielia associated to internal spinal cord hemorrhage
Post-traumatic Syringomielia: complication situated far from traumatism in the spine cord
From these seven groups both first ones include syringomielias related to posterior craneal base injuries that alter the cerebro spinal fluid (LCR) flow in the crossroads of the fourth ventricle, space subaracnoideo spinal, trunk, cerebellum and spinal cord. The last five groups are associated to alterations in the spinal LCR.dynamic
To understand the theories on the pathological mechanisms, the syringomielia can be divided in two big groups:
The related ones to anomalies in the posterior craneal base, in the craneo vertebral union and related to spinal cord injuries.
Anomalies in posterior craneal base and in the craneo vertebral union
Chiari malformation: they are three types. Chiari I is the decrease of the cerebellum tonsilas under the magnum foramen with a minimum of 5 mms, but in severe cases the decrease can come up to the average third of the spinal cord, besides the cerebro spinal bulb and the fourth ventricle are misplaced. The syringomielia repercussion in this type of malformation might be less of 1 %. The Chiari type II consists of a decrease of the cerebellum associated with any spinal disrafía. It can accompany of syringomielia up to 50 % of the cases of mielomeningocele. The association with hydrocephalic is also high.
Chiari's malformation type III is the migration to the flow of the cerebellum tonsils in presence of encefalocele. The association with syringomielia may come to 22 %.
Bone anomalies, such us platibasia, basil impression and the posterior cranial base size decrease.
Injuries in the Magnum foramen such as tumors (meningioma) or inflammatory masses.
Presence of secondary membranes due to inflammation (meningitis), hemorrhages, cysts aracnoidales, etc.
Spinal injuries.
The spinal abnormalities associated to syringomielia have as common factor that they affect in one or another way the subaracnoídeo space to this level. There are different reasons:
Spinal cord tumors
Meningea Inflammation: meningitis.
Vascular malformations.
Cerebro spinal traumatism.
Others
There are many theories on the mechanisms of syringomielia production. None of them explains completely either its pathology or its association with different pathologies, but they all need a clear understanding on LCR traffic.
The LCR is produced by the cerebral ventricles coroideos plexuses and from there it circulates through the subaracnoideo space across opened holes in the ventricle IV level (holes of Luschka and Magendie).
In the subaracnoídeo space, the LCR moves on the convexity and on the spinal region finally to be absorbed in the aracnoideas hairiness of the venous longitudinal top bosom. The LCR traffic "engine"are the pressure waves generated by the systole in the nervous central system vessels and for the pressure changes that are generated by respiratory movements. The pressures generated on the LCR are distributed rapidly and equitably in the whole subaracnoídeo space, in the spinal space as much as in the convexity, therefore any discontinuity in the mentioned space will produce potentially gradients of beating pressure in certain zones.
Chiari in 1895 postulated that the syringomielia was the persistence of the central conduit of the spinal cord in presence of hydrocephalic. Nevertheless, only 10 % of syringomielia patients present hydrocephalic.
Gardner and Angel explained that due to a difficulty to LCR's exit through the exit holes in the ventricle IV, the central channel remained opened and "communicate across the Ovex, for what it was recommended to cover it with a chunk of muscle. They were thinking that LCR's beatings "were" "hammering" the central channel filling of LCR and expanding it. Nowadays it is known that approximately 10 % of the patients with Chiari I has a permeable Ovex . Besides the central channel does not communicate many syringomielias. Milhorat explained that ependimitis episodes, probably viral, were leading to obstruction to the normal rising flow expanding the central channel.
In the human being LCR's flow has not been shown through the central channel, but it is believed that ependimarias cells might produce LCR. Ball and Dayan proposed LCR's flow across perivascular spaces (of Virchow - Robin) that then were emptying in remnants of the central channel. Oldfield added s that due to the waves of the LCR, this one pass across perivascular spaces in presence of obstruction in the subaracnoídeo space into the Magnum foramen level.
It’s not clear how a cavity begins syringomiélic. The current theories explain its expansion, but not its formation. Williams developed the idea that the cavity expansion has an axial form due to Valsalva's maneuver and to the presence of an obstruction of the subaracnoídeo space, specially in the magnum foramen level, the epidural veins exercise axial tension that cannot balance themselves, forming pressure gradients in the LCR that end up by enlarging the cyst.
Actually some of the concepts are still used.
The principal pathology aspect is the obstruction of the subaracnoideo space in some region that does not allow the immediate balance in the rapid pressures changes to which the LCR is submitted, produced principally by the cardiac beatings, the breathing and Valsalva's maneuvers. Due to this dissociation spinal/cranial (Chiari's malformation, Magnum foramen injuries) or spinal / spinal (aracnoidales scars due to a trauma, meningitis, tumors, etc), LCR flow across perivascular spaces and forms cavities. Besides it has been postulated that in the Chiari Malformation, the ruptured tonsils might act as a valve on the LCR, stopping the flow from the spinal region towards the cranial region when the patient is submitted to Valsalva's maneuvers.
This will produce a major pressure in the subaracnoídeo space on the magnum foramen and once stops the maneuver, a negative pressure in the subaracnoídeo spinal produces a real suction across the central channel in the spinal cord.
Syringomielia associated with spinal cord tumors
The syringomielia appears between (among) 25% and 58 % of the spinal cord tumors. The majority of them are ependinoma,or astrocitoma. Most of the times the cyst is located on the tumor, nevertheless it can be in any place of the spinal cord, even distant to the injury. There are postulated as reasons, vascular alterations produced by the tumor, which will go to necrosis or hemorrhage and to the formation of spinal cord cavities fundamentally. The liquid of these cavities can be rich in proteins, which will give a sallow aspect.
Syringomielia associated with trauma:
It can appear between 1% and 4 % of the craneo spinal traumatism,
Generally it has a late evolution, appearing months or some years after the traumatic event. The clinical picture is associated to a late neurological progression. The secondary spinal cord cavities, the traumatic hematomielia, the LCR's flow blockade due to compression, glial damage and aracnoídea adherence progression are postulated as pathological mechanisms. Nevertheless it is admitted nowadays that most of the syringomielias associated with trauma happen in column traumatism, in which the spinal cord injury has been slight.
Syringomielia's Clinical picture
The syringomielia symptomatology is due to alterations produced by the cyst cavities although some patients will present symptoms derived from underlying pathology. This way, the chiari malformation patients can present cervical and occipital pain due to the decrease under the magnum foramen of structures that normally are above him.
A central spinal cord syndrome gives a clinical picture since the cavity takes place in the grey substance or in the central conduit. If the cavity extends to the bulb (syringobulbia) some bulbar symptoms will be able to appear expressed by alterations of low cranial nerves.
The central spinal cord syndrome consists in thermal and painful hipoestesia in certain spinal cord segments. This is called " suspended level " and it is due to the commitment of the sensitive routes in its way from the dorsal shaft in the spinal cord up to the espinotalámicos lateral beams
This crossing happens in the grey substance and the space is affected by central injuries, such as the syringomielia. Besides, if the cavity continues growing, they will compromise the pyramidal beams, giving signs of second motoneurona in the level of the injury and of the first motoneurona towards the flow.
Diagnosis
The syringomielia diagnosis is realized nowadays by magnetic resonance (RM). This examine shows the cyst cavity inside the spinal cord and its extension. Due to the liquid content, the image is estimated hipointense in T1 and hyperintense in T2. Some cavities associated with spinalcord tumors have a higher protein content, so what the image will show less hipointense liquid than the LCR in T1. In a longitudinal cut of the syringomielia the RM can show thin transverse partitions but the syringomielia cavity is actually one. Besides there exist at present, cinemas scenes that shows e LCR flow in the subaracnoídeo space or spinal cord cavities, all these are important aspects for investigation.
The RM allows seeing diseases associated to syringomielia, such as alterations in the posterior cranial base. In spinal cord tumors shows the tisular tumor masse and if there is a liquid tumor cavity so as if there is a closed or fared-off syringomielia to the cyst tumor, or both. Also they can be appreciated hemorrhage, isquemic, traumatic, or other consequences.
Syringomielia treatment
The treatment is difficult, since it is necessary to identify the pathologies associated to it and to measure their role. The cyst surgical treatment seeks to stop the neuralgic damage progression and eliminate the syringomielia causes.
To evaluate if a patient is a surgical treatment candidate, it is necessary to evaluate several factors, among them:
Patient condition:
Some patients suffer neurological hurt damage from long time ago, they are prostrated and dependent on other people. The surgery does not benefit them in general, the medical treatment is considered to be more suitable. The surgery may help these patients to avoid bulbar symptoms, since swallowing or respiratory alterations, decrease very much the quality of life and constitutes a risk.
Evolutionary neurological profile:
The patients, who present neurological problems in a period of time, can benefit from a surgery, on the other hand, in those who present neurological stability in a long time (2 years), observation is recommended.
Asymtomatic patients
RM images evolution has made possible to diagnose syringomielia without any symptoms. The protocol to follow in these kinds of patients is been very argued since, as soon as neurological symptoms appear it is slightly probable that they return with surgery. On the other hand, the asymtomatic syringomielia natural history is not clearly defined and probably in many cases will not give symptoms along the life. Actually theses patients are keep on observation for clinical course using the RM images.
Syringomielia types.
Probably it is the most important factor to consider, since treating the disease origin determines a better result.
The principal aim in Chiari malformation surgical treatment is the posterior cranial base decompression. To drain the cyst and liberate the entire aracnoidal adherence as much as possible. The cyst drainage may be realized for "syringostomia" procedure or derivative methods to conduct the liquid from the cyst to another cavity, such as the subaracnoídal, pleural or peritoneal space
In tumors the suitable treatment is the tumor resection, assuring the syringomielia opening, eventually - if the cyst has not been emptied - it is necessary to add a syringostomic procedure or a derivation at the surgical time.
Finally the endoscopic surgery advances probably will allow realizing some of these procedures in a less invasive form.
Surgical Treatment results.
Chiari's malformation: The current treatment consists of a cranial descompressive procedure and vertebral discharge (C1, C2) procedure. Using this technology, 30 to 40 % of the patients presents a decrease of the cervical and migraine pain so as a slight improvement of the paresis and the sensitive deficit. 40 % of them remains stable and 20 % deteriorates.
Factors o a bad diagnosis are: an evolution time of more than 2 years, the presence of ataxia, bulbar symptoms, atrophy and commitment of posterior vertebral column
Some authors add to the magnum foramen decompression the insertion of a syringosubaracnoídeo catheter with good results.
Syringomielia associated with tumors: The treatment consists of the tumor resection, with which the syringomielia is eliminated, in most of the cases. The prognosis is determined by the neurological previous condition and not by the presence of the cyst.
Traumatic Siringomielia: a better prognosis has been described. Up to 50 % would improve with any type of derivative and adherenciolisic procedure. The pain and paresis decreases .20 to 30 % of the patients remains stable from the neurological point of view.