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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

W ith a prevalence of 8.4 cases per 100,000 population, approximately 21,000 Americans have syringomyelia, a disorder in which a cyst forms within the spinal cord, resulting in myelopathy. 6 Symptoms of paralysis, sensory loss, and chronic pain commonly develop during the second through fifth decades of life. The natural history of syringomyelia is typically one of gradual, stepwise neurological deterioration extending over many years. 5 Syringomyelia is usually associated with an inferior position of the cerebellar tonsils through the foramen magnum: the

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Edward H. Oldfield

The case report by Takamura, et al. (Takamura Y, Kawasaki T, Takahashi A. A craniocervical injury—induced syringomyelia caused by central canal dilation secondary to acquired tonsillar herniation. Case report. J Neurosurg 95 (Spine 1): 122–127, July, 2001) nicely documents the stages of development of acquired Chiari I malformation and syringomyelia after trauma-induced hydrocephalus and impaction of the cerebellar tonsils into the foramen magnum. The main point of the report is the potential contribution of the anatomy of the central canal of the spinal cord

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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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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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John D. Heiss, Kendall Snyder, Matthew M. Peterson, Nicholas J. Patronas, John A. Butman, René K. Smith, Hetty L. DeVroom, Charles A. Sansur, Eric Eskioglu, William A. Kammerer and Edward H. Oldfield

S yringomyelia associated with spinal pathology is known as primary spinal syringomyelia (PSS). 3 , 4 The natural history of this and other forms of syringomyelia is one of gradual, stepwise deterioration over many years. 4 , 73 Primary spinal syringomyelia, which accounts for about one-sixth of all cases of syringomyelia, may be a consequence of traumatic injury, inflammatory conditions, or compressive lesions that compromise the subarachnoid space. 71 Posttraumatic syringomyelia manifests as progressive neurological deficit above the level of previous

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John D. Heiss, Giancarlo Suffredini, René Smith, Hetty L. DeVroom, Nicholas J. Patronas, John A. Butman, Francine Thomas and Edward H. Oldfield

S yringomyelia is more often associated with CM-I than any other etiology. 17 , 18 , 37 The objective of surgical treatment of syringomyelia associated with the CM-I is to decompress the cerebellar tonsils, eliminate the syrinx, and prevent the progression of myelopathy. A reduced syrinx size, which is associated with disease stabilization, occurs after craniocervical decompression or syrinx fluid shunting. Unlike craniocervical decompression, syrinx shunting does not address the underlying cause of the syringomyelia, requires invasion of the spinal cord

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Russell R. Lonser, John D. Heiss and Edward H. Oldfield

Syringomyelia can be associated with Chiari malformation, spinal neoplasms, trauma, arachnoiditis, and other structural spinal lesions. 1 Our patient had two potential underlying causes for a cervicothoracic syrinx: acquired Chiari I malformation and a spinal neoplasm. This 18-year-old woman with von Hippel—Lindau (VHL) disease suffered from increasingly intense occipital headaches. Magnetic resonance (MR) imaging revealed two contrast-enhancing lesions in the right cerebellar hemisphere ( Fig. 1A ), herniation of the cerebellar tonsils to C-1 ( Fig. 1B ), and

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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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Russell R. Lonser, John A. Butman and Edward H. Oldfield

Peritumoral cysts, those arising immediately adjacent to the tumor mass, are frequently associated with brain and spinal cord lesions (syringomyelia). Analysis of recent evidence has indicated that peritumoral edema and ultimately cyst formation associated with central nervous system hemangioblastomas are initiated by increased tumor vascular permeability and raised tumor interstitial pressure that extravasates plasma into the surrounding tissues. 1 This process was documented on magnetic resonance (MR) imaging in a patient with an intramedullary spinal

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Neurosurgical Forum: Letters to the editor To The Editor Arjun D. Sehgal , M.D., M.B.B.S., F.A.C.S., F.I.C.S. Sehgal's Neurological Research Institute New Delhi, India 811 813 I read with considerable interest the recent article by Oldfield, et al. (Oldfield EH, Muraszko K, Shawker TH, et al: Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. J Neurosurg 80: 3–15, January, 1994). I appreciate their hypothesis on