Greitz Dan
Department of Neuroradiology and MR Research Center, Karolinska University Hospital, S-171 76, Stockholm, Sweden.
Neurosurg Rev. 2006 Oct;29(4):251-63; discussion 264. doi: 10.1007/s10143-006-0029-5. Epub 2006 May 31.
The pathophysiology of syringomyelia development is not fully understood. Current prevailing theories suggest that increased pulse pressure in the subarachnoid space forces cerebrospinal fluid (CSF) through the spinal cord into the syrinx. It is generally accepted that the syrinx consists of CSF. The here-proposed intramedullary pulse pressure theory instead suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid. A new principle is introduced implying that the distending force in the production of syringomyelia is a relative increase in pulse pressure in the spinal cord compared to that in the nearby subarachnoid space. The formation of a syrinx then occurs by the accumulation of extracellular fluid in the distended cord. A previously unrecognized mechanism for syrinx formation, the Bernoulli theorem, is also described. The Bernoulli theorem or the Venturi effect states that the regional increase in fluid velocity in a narrowed flow channel decreases fluid pressure. In Chiari I malformations, the systolic CSF pulse pressure and downward motion of the cerebellar tonsils are significantly increased. This leads to increased spinal CSF velocities and, as a consequence of the Bernoulli theorem, decreased fluid pressure in narrow regions of the spinal CSF pathways. The resulting relatively low CSF pressure in the narrowed CSF pathway causes a suction effect on the spinal cord that distends the cord during each systole. Syringomyelia develops by the accumulation of extracellular fluid in the distended cord. In posttraumatic syringomyelia, the downwards directed systolic CSF pulse pressure is transmitted and reflected into the spinal cord below and above the traumatic subarachnoid blockage, respectively. The ensuing increase in intramedullary pulse pressure distends the spinal cord and causes syringomyelia on both sides of the blockage. The here-proposed concept has the potential to unravel the riddle of syringomyelia and affords explanations to previously unanswered clinical and theoretical problems with syringomyelia. It also explains why syringomyelia associated with Chiari I malformations may develop in any part of the spinal cord including the medullary conus. Syringomyelia thus preferentially develops where the systolic CSF flow causes a suction effect on the spinal cord, i.e., at or immediately caudal to physiological or pathological encroachments of the spinal subarachnoid space.
脊髓空洞症发展的病理生理学尚未完全明了。当前流行的理论认为，蛛网膜下腔脉压升高迫使脑脊液（CSF）通过脊髓进入空洞。人们普遍认为空洞由脑脊液构成。本文提出的髓内脉压理论则认为，脊髓空洞症是由脊髓内脉压升高引起的，且空洞由细胞外液构成。引入了一个新原理，即脊髓空洞症形成过程中的扩张力是脊髓内脉压相对于附近蛛网膜下腔脉压的相对升高。然后，细胞外液在扩张的脊髓内积聚导致空洞形成。还描述了一种此前未被认识的空洞形成机制——伯努利定理。伯努利定理或文丘里效应表明，在狭窄的流动通道中流体速度的局部增加会降低流体压力。在Chiari I畸形中，收缩期脑脊液脉压和小脑扁桃体向下运动显著增加。这导致脊髓脑脊液速度增加，并且由于伯努利定理，脊髓脑脊液通路狭窄区域的流体压力降低。在狭窄的脑脊液通路中产生的相对较低的脑脊液压力对脊髓产生吸引作用，在每个收缩期使脊髓扩张。脊髓空洞症通过细胞外液在扩张的脊髓内积聚而发展。在创伤后脊髓空洞症中，向下的收缩期脑脊液脉压分别在创伤性蛛网膜下腔阻塞下方和上方的脊髓中传导和反射。随之而来的髓内脉压升高使脊髓扩张，并在阻塞两侧导致脊髓空洞症。本文提出的概念有可能解开脊髓空洞症之谜，并为脊髓空洞症以前未得到解答的临床和理论问题提供解释。它还解释了为什么与Chiari I畸形相关的脊髓空洞症可能在脊髓的任何部位发生，包括圆锥。因此，脊髓空洞症优先发生在收缩期脑脊液流动对脊髓产生吸引作用的部位，即在脊髓蛛网膜下腔生理或病理侵犯处或其紧邻尾侧。
