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Edward H. Oldfield, Karin Muraszko, Thomas H. Shawker and Nicholas J. Patronas

T he mechanisms of origin, maintenance, and progression of syringomyelia associated with Chiari I malformation of the cerebellar tonsils, manifested as a tonsillar herniation through the foramen magnum associated with a normal hindbrain, 11, 12 are controversial. 3, 5, 6, 40, 65 Two principal theories have been proposed. The “hydrodynamic theory,” initially proposed by Gardner and colleagues, 28, 29, 31 attributes extension of syringomyelia to the “water-hammer” effect of pulsatile transmission of cerebrospinal fluid (CSF) from the fourth ventricle via a

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John D. Heiss, Nicholas Patronas, Hetty L. DeVroom, Thomas Shawker, Robert Ennis, William Kammerer, Alec Eidsath, Thomas Talbot, Jonathan Morris, Eric Eskioglu and Edward H. Oldfield

Object

Syringomyelia causes progressive myelopathy. Most patients with syringomyelia have a Chiari I malformation of the cerebellar tonsils. Determination of the pathophysiological mechanisms underlying the progression of syringomyelia associated with the Chiari I malformation should improve strategies to halt progression of myelopathy.

Methods

The authors prospectively studied 20 adult patients with both Chiari I malformation and symptomatic syringomyelia. Testing before surgery included the following: clinical examination; evaluation of anatomy by using T1-weighted magnetic resonance (MR) imaging; evaluation of the syrinx and cerebrospinal fluid (CSF) velocity and flow by using phase-contrast cine MR imaging; and evaluation of lumbar and cervical subarachnoid pressure at rest, during the Valsalva maneuver, during jugular compression, and following removal of CSF (CSF compliance measurement). During surgery, cardiac-gated ultrasonography and pressure measurements were obtained from the intracranial, cervical subarachnoid, and lumbar intrathecal spaces and syrinx. Six months after surgery, clinical examinations, MR imaging studies, and CSF pressure recordings were repeated. Clinical examinations and MR imaging studies were repeated annually. For comparison, 18 healthy volunteers underwent T1-weighted MR imaging, cine MR imaging, and cervical and lumbar subarachnoid pressure testing.

Compared with healthy volunteers, before surgery, the patients had decreased anteroposterior diameters of the ventral and dorsal CSF spaces at the foramen magnum. In patients, CSF velocity at the foramen magnum was increased, but CSF flow was reduced. Transmission of intracranial pressure across the foramen magnum to the spinal subarachnoid space in response to jugular compression was partially obstructed. Spinal CSF compliance was reduced, whereas cervical subarachnoid pressure and pulse pressure were increased. Syrinx fluid flowed inferiorly during systole and superiorly during diastole on cine MR imaging. At surgery, the cerebellar tonsils abruptly descended during systole and ascended during diastole, and the upper pole of the syrinx contracted in a manner synchronous with tonsillar descent and with the peak systolic cervical subarachnoid pressure wave. Following surgery, the diameter of the CSF passages at the foramen magnum increased compared with preoperative values, and the maximum flow rate of CSF across the foramen magnum during systole increased. Transmission of pressure across the foramen magnum to the spinal subarachnoid space in response to jugular compression was normal and cervical subarachnoid mean pressuree and pulse pressure decreased to normal. The maximum syrinx diameter decreased on MR imaging in all patients. Cine MR imaging documented reduced velocity and flow of the syrinx fluid. Clinical symptoms and signs improved or remained stable in all patients, and the tonsils resumed a normal shape.

Conclusions

The progression of syringomyelia associated with Chiari I malformation is produced by the action of the cerebellar tonsils, which partially occlude the subarachnoid space at the foramen magnum and act as a piston on the partially enclosed spinal subarachnoid space. This creates enlarged cervical subarachnoid pressure waves that compress the spinal cord from without, not from within, and propagate syrinx fluid caudally with each heartbeat, which leads to syrinx progression. The disappearance of the abnormal shape and position of the tonsils after simple decompressive extraarachnoidal surgery suggests that the Chiari I malformation of the cerebellar tonsils is acquired, not congenital. Surgery limited to suboccipital craniectomy, C-1 laminectomy, and duraplasty eliminates this mechanism and eliminates syringomyelia and its progression without the risk of more invasive procedures.

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Nicholas M. Wetjen, John D. Heiss and Edward H. Oldfield

C hiari malformation Type I is a disorder in which the cerebellar tonsils protrude through the foramen magnum and into the spinal canal. This anomaly is the leading cause of syringomyelia and occurs with or without associated osseous abnormalities at the craniovertebral junction. 3–5 , 7–10 , 12–14 In contrast to other types of Chiari malformations, which usually present in infancy, CM-I tends to present during or after the second decade of life. Overcrowding of the hindbrain by an underdeveloped posterior fossa commonly causes tonsillar ectopia in CM

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Elizabeth C. Clarke, Marcus A. Stoodley and Lynne E. Bilston

C hiari malformation Type I is an abnormality characterized by inferior protrusion of the cerebellar tonsils through the foramen magnum. Approximately two-thirds of patients with CM-I also develop syringomyelia, 8 but it is not clear why some patients with CM-I develop syringomyelia and others do not. The possibility of prevention of syringes and the optimal treatment of resistant syringes is unclear because the pathogenesis of syringomyelia remains unknown. Several theories on the pathogenesis of syringomyelia have been formed over the years

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Sarah J. Hemley, Lynne E. Bilston, Shaokoon Cheng and Marcus A. Stoodley

C hiari malformation Type I is an abnormality at the craniocervical junction, characterized by the caudal displacement of the cerebellar tonsils into the spinal canal and reduction of the subarachnoid space at the foramen magnum. A CM-I is the underlying condition most commonly associated with syringomyelia, producing isolated enlargements of the central canal. Neurological deficits such as sensory loss and muscular atrophy often occur when these canalicular syringes rupture through the ependymal lining into the cord substance. 10 , 35 , 36 It has

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Jakub Godzik, Michael P. Kelly, Alireza Radmanesh, David Kim, Terrence F. Holekamp, Matthew D. Smyth, Lawrence G. Lenke, Joshua S. Shimony, Tae Sung Park, Jeffrey Leonard and David D. Limbrick

C hiari malformation Type I (CM-I) is a developmental abnormality of the craniovertebral junction (CVJ), often associated with spinal cord abnormalities such as syringomyelia and scoliosis. 10 , 33 The rate of scoliosis in pediatric patients with CM-I has been reported to be as high as 80% in those with concurrent syringomyelia. 6 , 10 , 16 , 20 , 31 Some authors have speculated that the etiology of scoliosis in such patients is related to the effect of the expanding spinal cord syrinx on the function of medially located motor neurons; the resulting

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Christian Ewelt, Susanne Stalder, Hans-Jakob Steiger, Gerhard Hildebrandt and Raoul Heilbronner

T he phenomenon of syringomyelia is a longitudinal cavity within the spinal cord that generally extends over several segments. Its most common cause is a structural lesion in the form of an Arnold-Chiari malformation Type I or II at the foramen magnum. Other causes include localized meningeal fibrosis due to spinal cord trauma or as a consequence of infection, tumor, or surgery. During the last few years, spinal cordectomy has become more important in the surgical treatment of syringomyelia, as revealed by recent publications' reference to this topic. 6 , 7

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Takaichi Suehiro, Takanori Inamura, Yoshihiro Natori, Masayuki Sasaki and Masashi Fukui

F ourth ventricle outlet obstruction is a rare syndrome that is associated with hydrocephalus and syringomyelia, which are frequently found in patients with Chiari malformation; such an obstruction is caused by chronic tonsillar herniation. 17 Symptomatic hydrocephalus and syringomyelia have been treated by decompression of the posterior fossa, ventriculoperitoneal or Torkildsen shunt placement, and neuroendoscopic third ventriculostomy. 3, 19 We report on a patient in whom neuroendoscopic third ventriculostomy was used successfully to treat hydrocephalus and

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Thomas H. Milhorat, Harrison T. M. Mu, Carole C. LaMotte and Ade T. Milhorat

C entral pain characterized by burning dysesthesia and hyperpathia is a common and sometimes disabling symptom in patients with syringomyelia. 32, 34, 66, 67 A similar syndrome is reported by patients with traumatic paraplegia 10, 16, 38, 63 and other intrinsic spinal cord lesions such as intramedullary tumors 14, 37 and multiple sclerosis. 47, 54 Although the phenomenon of central pain is usually attributed to deafferentation hyperactivity, 11, 57, 62 there is limited information concerning the role played by pain-modulating neuropeptides. Previous

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John C. Oakley, George A. Ojemann and Ellsworth C. Alvord Jr.

P osttraumatic syringomyelia is a rare but well recognized sequela of spinal cord injury, occurring in about 1.8% of paraplegics and less than 0.5% of quadriplegics. 1 We have recovered 93 cases from the complete review of the subject to 1973 by Barnett, et al. , 1 and from the subsequent literature. 2, 4, 8, 11, 12, 14 Eight of these cases were verified postmortem, six with good documentation; 1, 3, 7, 9, 10 surgical verification was available for 38 of the remaining 85 cases. 2, 4, 7, 12 How these syringes develop is still controversial. Following