Pathogenesis of syringomyelia associated with Chiari type 1 malformation: review of evidences and proposal of a new hypothesis

Abstract

The exact pathogenesis of syringomyelia associated with Chiari type 1 malformation is unknown, although a number of authors have reported their theories of syrinx formation. The purpose of this review is to understand evidences based on the known theories and to create a new hypothesis of the pathogenesis. We critically review the literatures on clinicopathological, radiological, and clinical features of this disorder. The previously proposed theories mainly focused on the driven mechanisms of the cerebrospinal fluid (CSF) into the spinal cord. They did not fully explain radiological features or effects of surgical treatment such as shunting procedures. Common findings of the syrinx in clinicopathological studies were the communication with the central canal and extracanalicular extension to the posterior gray matter. Most of the magnetic resonance imaging studies demonstrated blockade and alternated CSF dynamics at the foramen magnum, but failed to show direct communication of the syrinx with the CSF spaces. Pressure studies revealed almost identical intrasyrinx pressure to the subarachnoid space and decreased compliance of the spinal CSF space. Recent imaging studies suggest that the extracellular fluid accumulation may play an important role. The review of evidences promotes a new hypothesis of syrinx formation. Decreased absorption mechanisms of the extracellular fluid may underlie the pathogenesis of syringomyelia. Reduced compliance of the posterior spinal veins associated with the decreased compliance of the spinal subarachnoid space will result in disturbed absorption of the extracellular fluid through the intramedullary venous channels and formation of syringomyelia.

Idiopathic syringomyelia: retrospective case series, comprehensive review, and update on management

“…Moreover, most studies have not consistently identified a pressure gradient that would favor CSF flow into the syrinx from the subarachnoid space. 17,19 It has been noted that delayed CT myelography after intrathecal injection of metrizamide has demonstrated enhancement of syringomyelic cavities. 24 In their review, Koyanagi and Houkin 19 reported that these results are not specific to syringomyelia and that delayed clearance of the contrast from syrinx cavities may explain the delayed visualization on CT myelography.…”

“…19 The exact mechanism, however, is still debated. Greitz 10 described the concept of intramedullary pulse pressure causing cord distension and subsequent cavitation.…”

Effect of Tonsillar Herniation on Cyclic CSF Flow Studied with Computational Flow Analysis

“…In the Chiari I malformation, CSF flows with higher velocities than in normal subjects, 1,4,5 and pressures are increased. 5 The hyperdynamic CSF flow and altered pressure dynamics in the Chiari malformation hypothetically have a role in the pathogenesis of syringomyelia, 6,7 motor and sensory abnormalities, headache, and so forth associated with the Chiari I malformation. 5 The effect of tonsillar herniation on CSF flow dynamics, therefore, needs further elaboration.…”

Multimodal evaluation of CSF dynamics following extradural decompression for Chiari malformation Type I

“…13,15 The need for potential reoperation given inadequate symptom resolution is balanced by the lower complication rate. 9,14 However, others argue that the complication rate using an intradural opening with duraplasty is near negligible. 20 In a comparison of duraplasty with intradural manipulation and dural splitting, the latter led to faster operating times, shorter hospital stays, and therefore lower total hospital costs while yielding comparable clinical results.…”

“…14,21 Dynamic imaging studies therefore provide additional utility in assessing the degree of impairment. Some authors describe using ultrasonography with color Doppler imaging in addition to MRI in order to demonstrate anatomical compression as well as impaction of CSF flow.…”