Dilatation Of Central Canal Research Articles

The first descriptions of syringomyelia

The historical significance of the paper by Jacob Lockhart Clarke and John Hughlings Jackson was eloquently presented.1 Claims of ‘first’ descriptions, however, are almost always subject to interpretation. The first description of the clinical syndrome of syringomyelia is generally attributed to Sir William Gull (1816–1890), who presented in 1862 a case of progressive atrophy of the hands.2 He had a lasting interest in spinal cord pathology, his description of paraplegia forming a large part of the Goulstonian lectures he delivered in 1848. It is conceivable that Gull and Clarke interacted at Guy's Hospital, where the former spent his career and the latter studied towards becoming a licentiate of the Society of Apothecaries. The first description of the term ‘syringomyelia’ came in 1827 by Charles Prosper Ollivier d'Angers (1796–1845), who published a case of spinal cord cavity in continuity with the fourth ventricle. Changing career from the military, having lost in the battle of Waterloo, he studied medicine in Paris. He was a contemporary of Francois Magendie (1783–1855) reflecting the growing interest in Parisian medicine in the structure and function of the central nervous system. Interested in comparative embryology and anatomical pathology of the spinal cord, he published his treatise on the spinal cord and its diseases.3 The term appears in the second edition of three (1827); it was applied in a general manner to the existence of any canal or cavity within the cord, and d'Angers regarded a central canal as pathological. In his chapter dealing with the defects in the formation of the cord he writes: ‘Many anatomists have described a central canal in the spinal cord. Ch. Etienne, in his description of the cord, says that such a canal is always present, and that it is continued into the brain. This opinion is also held by Colombo, who compares the canal to that of a quill; it is likewise accepted by Piccolhomini, Bauhin, and Malpighi. I have, however, clearly demonstrated from the internal structure of the spinal cord that in its normal state it does not contain a central canal’. Through to the modern day there has been confusion as to the pathophysiology of syringomyelia. Amongst neurosurgeons the term hydromyelia is generally used for a dilated central canal, whereas syringomyelia refers to cystic cavities within the cord. Cystic cavities per se in the spinal cord had actually been described much earlier; by Johann Conrad Brunner (1653–1727) in ‘Misc. Nat. curios.’ in 1688 and Giovanni Battista Morgagni (1682–1771) in 1761 in his ‘Adversaria Anatomica VI’. Nevertheless, Charles Estienne (1503–1564), also known as Carolus Stephanus, contemporary of Andreas Vesalius, provided the first description of cavities in the spinal cord, but also of the entity of the central spinal canal, in his treatise ‘La dissection du corps Human’ (1543). In summary, Estienne's ‘first’ was an anatomical description and distinction between the spinal canal and cystic cord cavities. D'Angers’ ‘first’ was the coinage and use of the pathoanatomical term syringomyelia. Gull's ‘first’ was the correlation of anatomy to function and the description of the clinical syndrome of syringomyelia. Clarke and Jackson helped popularise the term in an era of evolution for British neurology.

Natural history of Chiari malformation Type I following decision for conservative treatment

The natural history of the Chiari malformation Type I (CM-I) is incompletely understood. The authors report on the outcome of a large group of patients with CM-I that were initially selected for nonsurgical management. The authors identified 147 patients in whom CM-I was diagnosed on MR imaging, who were not offered surgery at the time of diagnosis, and in whom at least 1 year of clinical and MR imaging follow-up was available after the initial CM-I diagnosis. These patients were included in an outcome analysis. Patients were followed clinically and by MR imaging for a mean duration of 4.6 and 3.8 years, respectively. Of the 147 patients, 9 had new symptoms attributed to the CM-I during the follow-up interval. During this time, development of a spinal cord syrinx occurred in 8 patients; 5 of these patients had a prior diagnosis of a presyrinx state or a dilated central canal. Spontaneous resolution of a syrinx occurred in 3 patients. Multiple CSF flow studies were obtained in 74 patients. Of these patients, 23 had improvement in CSF flow, 39 had no change, and 12 showed worsening CSF flow at the foramen magnum. There was no significant change in the mean amount of cerebellar tonsillar herniation over the follow-up period. Fourteen patients underwent surgical treatment for CM-I. There were no differences in initial cerebellar tonsillar herniation or CSF flow at the foramen magnum in those who ultimately underwent surgery compared with those who did not. In patients with CM-Is that are selected for nonsurgical management, the natural history is usually benign, although spontaneous improvement and worsening are occasionally seen.

Acute Central Canal Dilatation After Minimally Invasive Lateral Cervical Decompression Through the Frykholm Approach

A case report to describe the first case of an acute central canal dilatation after minimally invasive lateral cervical decompression. To emphasize the need of being aware of this rare spinal disorder. A holocord syrinx is known as a complication of Chiari malformation. Furthermore, it can occur spontaneously, after trauma or infection. A 63-year-old patient with a left-sided nerve root stenosis, C3/C4, because of uncovertebral and intervertebral joint osteoarthritis with paresis of the left deltoid muscle, underwent minimally invasive decompression of the C4 nerve root according to the Frykholm approach. An immediately postoperative recognizably complete paresis of the right arm was because of hydromyelia from the fourth ventricle down to the thoracic spine. A minimal edema of the spinal cord was present. No abnormality of the spinal cord had been detected on preoperative magnetic resonance imaginary (MRI).At revision surgery high pressure was found within the hydromyelia. Subarachnoid drainage did not improve the neurologic deficits. On account of increasing edema of the spinal cord paraplegia developed, which almost completely resolved after further revision. The reason for the hydromyelia is unclear. Routinely used MRI is not able to detect a collapsed central canal of the spinal cord. Acute hydromyelia causes permanent neurologic deficits whereas edema might lead to transient disturbances.

Terminal ventriculostomy as an adjuvant treatment of complex syringomyelia: a case report and review of the literature

Complex syringomyelia is multifactorial, and treatment strategies are highly individualized. In refractory cases, sectioning of the filum terminale, also known as terminal ventriculostomy, has been described as a potential adjuvant treatment to alleviate syrinx progression. A 10-year-old boy with a history of arachnoiditis presented with complex syringomyelia, progressive lower extremity motor weakness, and spasticity. Previously, he had failed spinal cord detethering and direct syrinx shunting. Imaging studies demonstrated a holocord syrinx extending to the level of his conus medullaris and into the filum terminale. The patient underwent an uncomplicated lumbar laminectomy and transection of the filum terminale. Operative pathologic specimens demonstrated a dilated central canal within the filum. Postoperative imaging demonstrated significant reduction in the diameter of the syrinx. At follow-up, the patient's motor symptoms had improved. Terminal ventriculostomy may be a useful adjuvant in treating caudally placed syringes refractory to other treatments. This procedure carries low neurological risk and involves no hardware implantation. In select cases, terminal ventriculostomy may help preserve neurological function in the face of otherwise progressive syringomyelia.

Response to Dr. Suhas Udayakumaran concerning the paper by Martínez-Lafe JF et al. ‘Syringomyelia with quadriparesis in CSF shunt malfunction: a case illustration’, Child's Nervous System, DOI 10.1007/s00381-010-1165-3

1. We have treated several cases of shunted hydrocephalus accompanied by central canal dilatation by simply revising the shunt. In all of them, the hydromyelia resolved after this procedure. The situation of the reporte patient seemed more complex to us, given that apparently the valve was functioning appropriately. The ventricles were slightly dilated due to the increase in pressure of his externally adjustable valve, a maneuver that we undertook to prevent ventricular collapse. 2. We used the term “trapped fourth ventricle” to refer to a dilated ventricle as was evident in previous magnetic resonance (MR) studies performed to the patient. This isolated ventricular cavity most probably resulted from prior obstruction at the foramen magnum comprising the lateral foramina and the neighboring cerebellar tonsils from the one part, and from the other to functional kinking of the aqueduct. Dr. Udayakumaran is right in commenting that the patency of the central canal in anatomical communication with the fourth ventricle strictly contradicts the assertion of the existence of a complete block to CSF circulation. 3. The nature of the obstruction of CSF pathways at the foramen magnum was most probably related to adhesions secondary to his posthemorrhagic hydrocephalus. Why these adhesions did not involve the entry of CSF to the central canal remains elusive. Perhaps, during the evolution of the patient's hydrocephalus, these adhesions, being weaker, might have broken by the pulsations from the fourth ventricle. 4. The most difficult issue for us was to suspect the origin of the quadriparesis and to perform the spinal MR, as the patient previously had a milder quadriparesis as a sequel of his intraventricular hemorrhage. 5. Regarding treatment we were not confident on performing an endoscopic third ventriculostomy due to the areabsortive nature of the hydrocephalus together with his worsening condition that would not give us time to wait for the results of this procedure.

Defining the line between hydromyelia and syringomyelia. A differentiation is possible based on electrophysiological and magnetic resonance imaging studies

With the frequent use of magnetic resonance imaging (MRI), patients with subtle and diffuse symptoms due to small syrinx cavities increasingly present to neurosurgical care. In this respect, a dilated central canal, hydromyelia, must be separated from patients with true syringomyelia with an underlying disorder, as they do not share clinical and radiological features. We hypothesize that a differentiation of these two entities with distinct diagnostic tools is possible. To describe the entity of hydromyelia, we excluded all patients from the syringomyelia database (n = 142) with any obvious cause of a syringomyelia, any objective neurological deficits on clinical examination, pathological results on electrophysiological monitoring (SSEP, MEP, silent periods) or a widening of the spinal cord cavity of more than 6 mm on MRI [routine acquisitions with FLAIR, T1/T2-weighted images, Cine and CISS (constructive interference in steady-state) studies]. Life quality was assessed through SF-36 questionnaires and an individualized questionnaire for the clinical history, pain and alternative therapies. Forty patients (15 males/25 females) matched the criteria of a hydromyelia. With a mean age of 36.7 years (range 11-62), they almost all presented with pain (79%) or dysaesthesia of the limbs, with some having been an incidental finding (10%). Over a follow-up time of 36.9 months (range 6-93) there was no neurological or radiological deterioration. Patients with a hydromyelia do not share clinical or radiological characteristics with patients harbouring a true syringomyelia. As hydromyelia does not represent a disease with an underlying pathology, no clinical or radiological progression has been seen. With sophisticated diagnostic tools to rule out any pathology this subset of patients can be identified.

Syringomyelia with obstructive hydrocephalus at the foramens of Luschka and Magendie successfully treated by endoscopic third ventriculostomy

Background Syringomyelia rarely accompanies hydrocephalus except for the cases with Chiari malformation, and the efficacy of endoscopic third ventriculostomy for this entity is undetermined. Case Report A 55-year-old man developed sensory disturbance and discrete movement disturbance on the bilateral upper limb during the past 3 years. On admission, he presented with slight tetraparesis and hyperreflection on his lower limbs with rectovesical dysfunction. Preoperative MR imaging demonstrated marked enlargement of the lateral ventricles as well as the third and fourth ventricle due to obstruction of the foramens of Luschka and Magendie. Spine MR imaging showed longitudinal dilatation of the central canal from the cerebrospinal junction toward the thoracic level with communication to the fourth ventricle, whereas Chiari malformation and tight cisterna magna were absent. He was successfully treated by ETV. The patient significantly recovered from his symptoms postoperatively, and MR imaging after surgery showed apparent shrinkage of the syrinx as well as the ventricles. Conclusion The efficacy of the normalization of cerebrospinal fluid circulation and subsequent improvement of the syringomyelia in the present case may suggest that ETV could be a therapeutic choice for syringomyelia associated with hydrocephalus due to the obstruction of the foramens of Luschka and Magendie, especially when the connection between the ventricular system and the dilated central canal is evident, and may give a clue to the explanation for Gardner's hydrodynamic theory.

Ascending central canal dilation and progressive ependymal disruption in a contusion model of rodent chronic spinal cord injury

BackgroundChronic spinal cord injury (SCI) can lead to an insidious decline in motor and sensory function in individuals even years after the initial injury and is accompanied by a slow and progressive cytoarchitectural destruction. At present, no pathological mechanisms satisfactorily explain the ongoing degeneration.MethodsAdult female Sprague-Dawley rats were anesthetized laminectomized at T10 and received spinal cord contusion injuries with a force of 250 kilodynes using an Infinite Horizon Impactor. Animals were randomly distributed into 5 groups and killed 1 (n = 4), 28 (n = 4), 120 (n = 4), 450 (n = 5), or 540 (n = 5) days after injury. Morphometric and immunohistochemical studies were then performed on 1 mm block sections, 6 mm cranial and 6 mm caudal to the lesion epicenter. The SPSS 11.5 t test was used to determine differences between quantitative measures.ResultsHere, we document the first report of an ascending central canal dilation and progressive ependymal disruption cranial to the epicenter of injury in a contusion model of chronic SCI, which was characterized by extensive dural fibrosis and intraparenchymal cystic cavitation. Expansion of the central canal lumen beyond a critical diameter corresponded with ependymal cell ciliary loss, an empirically predictable thinning of the ependymal region, and a decrease in cell proliferation in the ependymal region. Large, aneurysmal dilations of the central canal were accompanied by disruptions in the ependymal layer, periependymal edema and gliosis, and destruction of the adjacent neuropil.ConclusionCells of the ependymal region play an important role in CSF homeostasis, cellular signaling and wound repair in the spinal cord. The possible effects of this ascending pathology on ependymal function are discussed. Our studies suggest central canal dilation and ependymal region disruption as steps in the pathogenesis of chronic SCI, identify central canal dilation as a marker of chronic SCI and provide novel targets for therapeutic intervention.

Spinal Sonography in Newborns and Infants - Part II: Spinal Dysraphism and Tethered Cord

Patients with cutaneous markers in the lumbo-sacral region as well as infants with bladder and bowel dysfunction, orthopedic anomalies and progressive neurological dysfunction are at risk for spinal dysraphism and tethered cord. Three types of spinal dysraphism can be distinguished: Type I - open spinal dysraphisms with a non-skin covered back mass; type II - closed spinal dysraphisms with a skin covered back mass; type III - occult spinal dysraphisms without a back mass. All spinal dysraphisms can be associated with a tethered cord, characterized by a low position of the conus medullaris below L3. Type I dysraphisms are meningomyeloceles and myeloceles, which are associated with CHIARI-II malformations characterized by the low position of the cerebellar vermis within the foramen magnum. Type II dysraphisms are lipomyeloceles, lipomyelomeningoceles, posterior meningoceles and myelocystoceles. Lipomeningoceles and lipomyelomeningoceles are characterized by a subcutaneous echogenic mass which communicates with the spinal canal and may cause tethered cord. Posterior meningoceles are, dorsal cystic space occupying lesions without internal neural tissue. Myelocystoceles are characterized by a cystic dorsal mass which communicates with a dilated central canal characteristic of syringo-hydromyelia. Type III dysraphisms without a back mass are frequently associated with cutaneous markers in the lumbo-sacral region. Sonographically dermal sinus tracts, diastematomyelia, tight filum and lipoma of the filum terminale and the caudal regression syndrome have to be distinguished. Dermal sinuses are characterized by an echogenic tract from the skin to the spinal canal, often associated with a spinal dermoid. Diastematomyelia is characterized by a complete or partial duplication of the spinal cord which can only be shown on axial images. Tight filum terminale or lipoma of the filum terminale is characterized by a thick echogenic filum with a diameter of more than 2 mm, and a conus below L3. All different forms of spinal dysraphisms and tethered cord can be diagnosed sonographically in the neonatal period as long as the spinal arches are not completely ossified.

Electron microscopic study of the progeny of ependymal stem cells in the normal and injured spinal cord

Background Spinal cord injury (SCI) is a common and often irreversible lesion that can incapacitate patients. Precursor cells in the spinal cord proliferate in response to trauma, and this proliferation can be enhanced by exogenous stimuli such as specific growth factors. In the present study, we examined electron microscopic detection of the proliferation, distribution, and phenotypic fate of these precursor cells in the injured adult rat spinal cord. Methods Adult female Sprague-Dawley rats weighing 250 to 300 g were divided into 3 groups. The first group consisted of spinal cord–injured animals with application of a 2.4-g clip extradurally around the spinal cord at the T1 level. A 26-g clip was applied in the second group. The third group included normal uninjured animals. Rats were sacrificed at 3 days, 3 weeks, and 6 weeks after injury. A segment of the spinal cord, 0.4 cm in length, encompassing the injury site was removed and was prepared for electron microscopy. Results Three days after mild injury (2.4-g clip), ependymal cells had begun to proliferate and had migrated from the central canal. They had a tendency to surround perivascular spaces close to the axons. The central canal rostral to the lesion site was widely dilated at 6 weeks postoperative in the moderately injured groups (26-g clip). The layer of ependymal cells lining the dilated canal showed reduction in cell height. Traumatic syringomyelic cavities were observed in all of the animals. There was an active proliferative response of the ependymal cells to injury. Large clusters of displaced ependymal cells associated with the dilated central canal were observed. Rests of ependymal cells were observed remote from the central canal with a tendency to form rosettes and accessory lumina 6 weeks after trauma. Fascicles of 3 to 8 fibers enclosed within an ependymal cell were a common finding among the ependymal clusters. There were also debris and some ependymal cells in the lumen. Conclusion Trauma induces active proliferation of precursor cells in the ependymal region. These cells may replace neural tissue lost to SCI and may assist in axonal regeneration.

Chronic changes in cerebrospinal fluid pathways produced by subarachnoid kaolin injection and experimental spinal cord trauma in the rabbit: their relationship with the development of spinal deformity

Post-traumatic cystic changes in cerebrospinal fluid (CSF) pathways such as ventriculomegaly and/or hydrosyringomyelia are not uncommon, but their characteristics have not yet been fully clarified. This study was designed to investigate the alterations affecting the CSF pathways in rabbits at a late stage, and to clarify the relationship between these changes and the development of spinal deformity. In this study, a total of 60 New Zealand white rabbits were used and they were segregated into four different groups of 15 animals each: sham-operation group, kaolin group, and kaolin plus mild trauma group and kaolin plus severe trauma group. The animals were subjected to radiological investigation using direct X-ray study and magnetic resonance imaging (MRI) after 4 months. The thoracic spinal cords of the animals were dissected after intracardiac perfusion-fixation with 10% formalin for light microscopy and 2.5% glutaraldehyde for transmission electron microscopic study. Following the sectioning and staining procedures, the histological characteristics of the spinal cords were evaluated with light microscopy and transmission electron microscopy. A spinal deformity developed in 90% in rabbits in both kaolin injection group and spinal trauma groups. MRI revealed generalized dilatation of the ventricular system and the central canal of the spinal cord after the kaolin injection with/without trauma in this study. Gross morphologic examination showed some enlargement of entire CSF pathways in these groups. All animals with central canal dilatation had mild or severe scoliotic and kyphotic deformities. In a light microscopic study, a denuded ependymal line and multicyst formations in periependymal areas were found in both kaolin injection and spinal trauma groups. Ultrastructurally, an apical flattening of the ependyma, microcysts in the ependymal cells, axonal degeneration, demyelination, and loss of ependymal cells adjacent mild spongy were found in the spinal cords of animals in these groups. To the best of our knowledge, this is the first study to investigate the chronic effects of spinal cord injury (SCI) on the CSF pathways and their relationship with the development of spinal deformity in an experimental model of kaolin injection and trauma, using MRI as well as light and transmission electron microscopy. In the light of this study, the severity of spinal cord injury on the development of some degenerative findings in the spinal cord was clear, but further clinical and experimental studies using dynamic imaging techniques will be valuable.

Origin of Macrophages in a Kaolin-Induced Model of Rat Syringomyelia

Animal experimental study. To study the origin of macrophages in a rat model of syringomyelia. Syringomyelia is a clinically important condition in which a cystic cavity forms within the spinal cord. This leads to significant delayed neurologic deterioration, which may be manifested as weakness, numbness, or pain. The pathophysiology and mechanism of syrinx formation remain unclear. Human autopsy findings have demonstrated a prominent accumulation of macrophages in relation to the syrinx. Similar observations have also been made in a previously established rat model of syringomyelia. Little is known about the origin and precise functions of these cells. Syrinx formation was induced by intraparenchymal injections of kaolin within the cervical spinal cords of 30 DA rat (RT7.1) radiation bone marrow chimeras reconstituted with bone marrow from RT7.2 congeneic donors. The distribution of macrophages was evaluated at survival times of 3 days, 1 week, and 4 weeks. Immunostaining of fresh-frozen spinal cord tissue was performed using specific antibodies against rat macrophage ED1 antigen and RT7.2 allele of CD45. This allowed donor-derived hematogenous (ED1+, RT7.2+) macrophages to be distinguished from native cells (ED1+, RT7.2-). Central canal dilatation was seen from 1 week. This was associated with extensive accumulation of ED1+ macrophages within the spinal cord parenchyma. A large influx of bone marrow-derived (ED1+, RT7.2+) macrophages was observed. However, a considerable proportion of resident microglia (RT7.2-) also upregulated ED1. These activated microglia demonstrated distinct morphologic features. Large numbers of macrophages were recruited from the bone marrow in kaolin-induced rat syringomyelia. However, a significant number of resident microglia upregulated their ED1 activity and appear to provide a substantial source of macrophages.

Fluid flow in an animal model of post-traumatic syringomyelia.

More than a quarter of patients with spinal cord injury develop syringomyelia, often with progressive neurological deficit. Treatment options remain limited and long-term failure rates are high. The current poor understanding is impeding development of improved therapies. The source and route of fluid flow into syringes has been investigated using cerebrospinal fluid (CSF) tracers. Previous work using a model of canalicular syringomyelia has shown that fluid enters the dilated central canal from perivascular spaces. The aim of this study was to determine the source and route of fluid flow in an animal model of extracanalicular (post-traumatic) syringomyelia. A model of post-traumatic syringomyelia was established in 25 Sprague-Dawley rats with intraparenchymal injections of quisqualic acid and kaolin-induced arachnoiditis. Rats survived for 6 weeks before injection of the CSF tracer horseradish peroxidase into the cisterna magna. Examination of the spatial distribution of horseradish peroxidase at 0, 3, 5, 10, or 20 min after injection was used to determine the route of fluid flow. Horseradish peroxidase rapidly spread to the ventromedian fissure, perivascular spaces, central canal, and extracanalicular syrinx. Flow occurred into the syrinx prior to significant perivascular flow in the rostral spinal cord. Preferential flow into the syrinx occurred from the perivascular spaces of the central penetrating branches of the anterior spinal artery in the grey matter. Transparenchymal flow into the syrinx was less prominent than perivascular flow. This is the first report of fluid flow within the spinal cord in a model of post-traumatic syringomyelia. Fluid from perivascular spaces moves preferentially into extracanalicular syringes and the surrounding parenchyma. Obstruction to CSF flow and loss of compliance from traumatic arachnoiditis might potentiate fluid flow in the perivascular space.

A craniocervical injury—induced syringomyelia caused by central canal dilation secondary to acquired tonsillar herniation

The authors report on a 19-year-old man with an acquired tonsillar herniation caused by a craniocervical junction injury in which serial magnetic resonance (MR) images demonstrated patent and isolated segments of the central canal participating in the dilation and then formation of a cervical syrinx. The patient was involved in a motor vehicle accident; he developed tonsillar herniation as a complication of subarachnoid and epidural hemorrhage, predominantly observed around the cisterna magna and upper cervical canal. Repeated MR images obtained over an 11-month period indicated the for mation and acute enlargement of the syrinx. Ten months after the accident, the patient presented with sensory disturbance in both upper extremities and spasticity due to syringomyelia. He underwent craniocervical decompressive surgery and doraplasty, which reduced the size of syringomyelia. The authors postulate that the patent central canal may play a role in determining the location of a syrinx remote from a focus of cerebrospinal fluid obstruction.

Embryonic brain precursors transplanted into kainate lesioned rat spinal cord.

Embryonic day 14 rat cerebral cortex-derived precursors were expanded with FGF2 and labeled with BrdU prior to being transplanted into the kainic acid-lesioned adult rat spinal cord. While these precursors give rise to cells with neuronal, astrocytic and oligodendroglial phenotypes vitro, they remained largely undifferentiated up to 12 weeks in vivo. Numerous BrdU-labeled cells were found in injured gray matter, and also lining the dilated central canal that sometimes accompanies these lesions. BrdU-labeled cells never co-expressed Map2ab, rarely co-expressed GFAP but often co-expressed nestin, even after 12 weeks in vivo. These observations suggest that the environment of the kainic acid-injured spinal cord is not hostile to transplanted embryonic cerebral cortex-derived precursors, but also is not conducive to their neuronal differentation.

Morphological study of experimental syringomyelia with kaolin-induced hydrocephalus in a canine model.

In this morphological study the authors investigated whether spinal cord cavitation, produced in young mongrel dogs that had been rendered hydrocephalic by cisternal injection of kaolin, consists of a dilated central canal or intramedullary cavities. Hydrocephalus was noted in 50 of 56 dogs treated with kaolin. Of the 50 hydrocephalic young dogs, 29 were shown to have central canal dilation that was prominent at the thoracic level and 21 to have cervical intramedullary cavities in the posterior column and/or the posterior horn. In 11 dogs from the latter group these cavities were demonstrated to have no communication with the central canal. This finding could not be explained by the hydrodynamic theory. On histopathological examination, myelomalacia and hemorrhagic infarction following ventricular shunting were noted adjacent to the cervical cavities, which suggested vascular impairment. A perfusion study revealed insufficient blood flow within the cervical cord at the level of the intramedullary cavities. A close correlation between the vascular insufficiency of the cervical cord and the pressure cone resulting from significant hydrocephalus was observed. The latter may cause cervicomedullary compression at the foramen magnum, affecting the venous drainage of the cervical cord below that level, resulting in intramedullary cavitation. Accordingly, vascular impairment was thought to play a significant role in the development of cervical syrinx formation in our kaolin model. The current results may provide a reasonable explanation for the formation of noncommunicating cervical syringomyelia in Chiari I malformation.

Syringomyelia

Eighteen autopsy cases of syringomyelia were studied neuropathologically. In six cases associated with Chiari II malformation, the central canal was patent from the fourth ventricle to the syrinx, and the syrinx was simply a dilated central canal. In four cases associated with Chiari I malformation, the syrinx was irregularly shaped and communicated with the subarachnoid space at the entry zone of the posterior nerve roots. In six cases associated with spinal cord or posterior fossa tumors, the syrinx was located adjacent to the tumor tissues, and occupied the medullary gray matter or the spinal intermediate zone and the ventral part of the posterior horn. With regard to the pathogenesis of syringomyelia, we concluded that in cases associated with Chiari II malformation, vermian protrusion and direct continuity between the fourth ventricle and the syrinx were essential. In cases associated with Chiari I malformation, in addition to tonsillar protrusion, communication between the syrinx and the subarachnoid space was thought to play an important role, and in cases associated with tumors, the circulatory disturbance due to the presence of the tumors caused the syrinx.

Hydromyelic hydrocephalus

The clinical features and pathophysiology of specific forms of hydromyelia are analyzed in this report together with the chronological changes of associated hydrocephalus. Nine patients were studied; all had hydromyelia with varying degrees of associated hydrocephalus. Clinically applicable classification systems were used to evaluate the progression of hydrocephalus (Stages I to IV) and to define the compartment isolated after shunting in the previously communicating cerebral ventricles (Types I to IV). Four patients had Stage IV disease (holoneural canal dilatation); one had Stage II and four had Stage I disease (both Stages I and II with supratentorial hydrocephalus). All patients were initially treated by ventriculoperitoneal shunting at an average age of 9.9 years. Five patients had progressive spinal symptoms before or after treatment of their hydrocephalus. Two patients had Type III isolation (an isolated rhombencephalic ventricle) with a functioning ventricular shunt; ventriculography confirmed a communication between the fourth ventricle and the hydromyelia, and both patients improved after placement of a shunt in the fourth ventricle. The remaining patients had Type IV isolation (isolated central canal dilatation) with a functioning ventricular shunt. This study indicates that in some cases the pathophysiology of hydromyelia is closely related to associated hydrocephalus. A new concept of the development of an isolated compartment after shunting is proposed to explain the progression of hydromyelia in these cases.

Experimental hydrocephalus and hydrosyringomyelia. Computertomographic studies

Two methods were used to induce a model of experimental hydrocephalus and hydrosyringomyelia in the cat: a) injection of kaolin into the cisterna magna and b) closure of the lateral apertures of the fourth ventricle with cotton swabs. The pathological changes in the brain ventricles and the central canal of the spinal cord were monitored and documented at regular intervals by computed tomography (CT). The CT method is particularly advantageous for studies of this kind because the animals can be examined frequently without risking disturbances in cerebro-spinal fluid dynamics or tissue damage that would result from introduction of contrast media into the ventricular system. Our results and others reported earlier suggest that the dilated central canal acts as a kind of spontaneous CSF deviation route from the ventricles to the subarachnoid space. In spite of the tendency of the animals to recover in a clinical sense, the internal CSF space continued to expand; in cats the disease is progressive, a fact that is readily evident in follow-up CTs. This characteristic indicates that the spontaneous "shunt system" from the fourth ventricle through the dilated central canal to the spinal CSF spaces does not function well enough. Possible explanations for hydrocephalus compensation and the development of hydrosyringomyelia in experimental animals are discussed.

Experimental hydrocephalus and hydrosyringomyelia in the cat. Radiological findings.

Fourty-six cats were made hydrocephalic and hydromyelic by means of an intracisternal kaolin injection. In 17 other cats hydrocephalus and syringohydromyelia were achieved by operative occlusion of the foramina Luschkae of the fourth ventricle. In both the kaolin treated animals and the animals whose outlets of the fourth ventricles were operatively obstructed a progressive dilatation of the ventricles and central canal occurred, which could be demonstrated and followed in 30 animals by ventriculography, myelography and/or contrast filling of the hydromyelic central canal. Coinciding with the dilatation of the central canal the clinical picture of a raised intracranial pressure due to obstructive hydrocephalus improved. The presented results suggest that the dilated central canal acts as a kind of natural by-pass between the ventricles and the spinal subarachnoid space. In order to determine the role of spinal kaolin arachnoiditis on spinal cyst formation and central canal dilatation in 13 animals, kaolin was locally applied in the lower thoracic region. The local spinal kaolin arachnoiditis had no influence on central canal dilatation or cyst formation.