Elucidating the pathophysiology of syringomyelia

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>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 T<jats:sub>1</jats:sub>-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 T<jats:sub>1</jats:sub>-weighted MR imaging, cine MR imaging, and cervical and lumbar subarachnoid pressure testing.</jats:p> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>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.</jats:p></jats:sec>

Decompression of the spinal subarachnoid space as a solution for syringomyelia without Chiari malformation

“…The optimal surgical management to eliminate this mechanism and to reduce the syrinx was proposed to be a procedure that could expand the CSF pathway at the foramen magnum: posterior fossa decompression, upper cervical laminectomy and augmenting duraplasty. 1 Phase contrast cine-MRI made it possible to evaluate the altered cerebrospinal¯uid dynamics in patients with Chiari I malformations. Postoperative changes in CSF¯ow pro®les included an increase in velocity magnitude and a change in the direction of¯ow from a previously constricted posterior fossa.…”

“…Anatomical repositioning of the tonsil, normalization of abnormal CSF¯ow pro®les after foramen magnum decompression or decompression of syrinx itself might explain the clinical improvement of the patients. 1 In the syringomyelia other than Chiari malformation, a similar but simpler concept is applied as there is no tonsillar herniation or complicating mechanism of syrinx propagation associated with it. There remains CSF¯ow obstruction and pathological change to the subarachnoid space, such as arachnoid adhesion or Figure 2 (a) T1-weighted sagittal view of thoraco-lumbar MRI shows the extent of syringomyelia to be di use, from upper thoracic to conus level (small arrows) with interruption at T9 to T12 level which is also the previous operation site (large arrows).…”

“…It is now believed that syringomyelia with Chiari malformation is developed as a result of pressure gradient and an aberrant CSF¯ow in the subarachnoid space at the cervicomedullary junction impacted with cerebellar tonsil. 1 However, the majority of previous reports on analysis of CSF¯ow dynamics in syringomyelia have been limited to cases of Chiari I malformation. In these reports, there has been a focus on the correlation of symptomatic improvement with quantitatively proven normalized¯ow or value for the velocity of CSF¯ow at the cervicomedullary junction after posterior fossa decompression.…”

Posterior fossa decompression with tonsillectomy in 104 cases of basilar impression, Chiari malformation and/or syringomyelia

“…In recent times, however, some authors 19,20 using X-ray, computed tomography and magnetic resonance imaging (MRI) examinations have also demonstrated that the posterior fossa volume, in the presence of BI and CM, is smaller than those observed in normal people. Milhorat et al 21 verified a decrease of 13.4 mL in the total volume of the posterior fossa and 40% (10.8 mL) in the CSF volume of this region.…”

Comparative study of duraplasty and non duraplasty in Chiari 1 malformation with syringomyleia our institute experience

“…Basic to all the procedures is enlargement of the foramen magnum with the intent of establishing relatively unimpeded flow of CSF from the cranial cavity to the spinal subarachnoid space. [5][6][7][8][9] In the present study, we review our experience with the treatment of CM1 in patients who underwent decompression with or without duraplasty and the correlation of clinical and imaging outcomes after 2 year of follow up.…”