National Institute of Neurological Disorders and Stroke, Surgical Neurology Branch, National Institute of Health, Bethesda, Maryland, USA.
J Neurosurg Spine. 2012 Nov;17(5):367-80. doi: 10.3171/2012.8.SPINE111059. Epub 2012 Sep 7.
The pathogenesis of syringomyelia in patients with an associated spinal lesion is incompletely understood. The authors hypothesized that in primary spinal syringomyelia, a subarachnoid block effectively shortens the length of the spinal subarachnoid space (SAS), reducing compliance and the ability of the spinal theca to dampen the subarachnoid CSF pressure waves produced by brain expansion during cardiac systole. This creates exaggerated spinal subarachnoid pressure waves during every heartbeat that act on the spinal cord above the block to drive CSF into the spinal cord and create a syrinx. After a syrinx is formed, enlarged subarachnoid pressure waves compress the external surface of the spinal cord, propel the syrinx fluid, and promote syrinx progression.
To elucidate the pathophysiology, the authors prospectively studied 36 adult patients with spinal lesions obstructing the spinal SAS. Testing before surgery included clinical examination; evaluation of anatomy on T1-weighted MRI; measurement of lumbar and cervical subarachnoid mean and pulse pressures at rest, during Valsalva maneuver, during jugular compression, and after removal of CSF (CSF compliance measurement); and evaluation with CT myelography. During surgery, pressure measurements from the SAS above the level of the lesion and the lumbar intrathecal space below the lesion were obtained, and cardiac-gated ultrasonography was performed. One week after surgery, CT myelography was repeated. Three months after surgery, clinical examination, T1-weighted MRI, and CSF pressure recordings (cervical and lumbar) were repeated. Clinical examination and MRI studies were repeated annually thereafter. Findings in patients were compared with those obtained in a group of 18 healthy individuals who had already undergone T1-weighted MRI, cine MRI, and cervical and lumbar subarachnoid pressure testing.
In syringomyelia patients compared with healthy volunteers, cervical subarachnoid pulse pressure was increased (2.7 ± 1.2 vs 1.6 ± 0.6 mm Hg, respectively; p = 0.004), pressure transmission to the thecal sac below the block was reduced, and spinal CSF compliance was decreased. Intraoperative ultrasonography confirmed that pulse pressure waves compressed the outer surface of the spinal cord superior to regions of obstruction of the subarachnoid space.
These findings are consistent with the theory that a spinal subarachnoid block increases spinal subarachnoid pulse pressure above the block, producing a pressure differential across the obstructed segment of the SAS, which results in syrinx formation and progression. These findings are similar to the results of the authors' previous studies that examined the pathophysiology of syringomyelia associated with obstruction of the SAS at the foramen magnum in the Chiari Type I malformation and indicate that a common mechanism, rather than different, separate mechanisms, underlies syrinx formation in these two entities. Clinical trial registration no.: NCT00011245.
伴有脊髓病变的脊髓空洞症的发病机制尚不完全清楚。作者假设，在原发性脊髓空洞症中，蛛网膜下腔阻滞有效地缩短了脊髓蛛网膜下腔（SAS）的长度，降低了顺应性和脊髓硬脑膜缓冲心脏收缩期脑扩张引起的蛛网膜下腔 CSF 压力波的能力。这会在每次心跳时产生过度的脊髓蛛网膜下腔压力波，作用于阻滞上方的脊髓，将 CSF 驱入脊髓并形成空洞。形成空洞后，扩大的蛛网膜下腔压力波会压迫脊髓外表面，推动空洞液，并促进空洞进展。
为了阐明病理生理学，作者前瞻性研究了 36 例伴有脊髓 SAS 阻塞的成年脊髓病变患者。手术前的检查包括临床检查；T1 加权 MRI 上的解剖学评估；在休息时、瓦尔萨尔瓦动作时、颈静脉压迫时以及 CSF 去除后（CSF 顺应性测量）测量腰段和颈段蛛网膜下腔的平均和脉搏压力；和 CT 脊髓造影。在手术过程中，从病变上方的 SAS 和病变下方的腰段蛛网膜下腔获得压力测量值，并进行心脏门控超声检查。手术后一周重复 CT 脊髓造影。手术后 3 个月，重复临床检查、T1 加权 MRI 和 CSF 压力记录（颈段和腰段）。此后每年重复临床检查和 MRI 研究。将患者的发现与已经接受 T1 加权 MRI、电影 MRI 和颈段和腰段蛛网膜下腔压力测试的 18 名健康个体的研究结果进行比较。
与健康志愿者相比，空洞症患者的颈段蛛网膜下腔脉搏压力增加（分别为 2.7 ± 1.2 与 1.6 ± 0.6 mmHg；p = 0.004），阻塞区下方硬脑膜鞘的压力传递减少，脊髓 CSF 顺应性降低。术中超声检查证实，脉搏压力波压缩了蛛网膜下腔阻塞上方脊髓的外表面。
这些发现与以下理论一致，即脊髓蛛网膜下腔阻滞会增加阻滞上方的脊髓蛛网膜下腔脉搏压力，在 SAS 的阻塞段产生压力差，从而导致空洞形成和进展。这些发现与作者之前研究的结果相似，该研究检查了 Chiari Ⅰ型畸形中 SAS 颅后窝阻塞与脊髓空洞症的发病机制，并表明这两种实体的空洞形成有一个共同的机制，而不是不同的、独立的机制。临床试验注册号：NCT00011245。
