History, controversy and pathogenesis

In this paper, we discuss the historical and pathophysiological aspects of syringomyelia. Defined as fluid cavities extending beyond several segments within the spinal cord this pathological entity is a condition with many po ssible causes. Hindbrain herniation is the commonest foramen magnum abnormality associated with the so called "hindbrain related syringomyelia". A history of birth i njury, a small posterior fossa, an arachnoid scarring of the basal cisterna , a segmentation abnormalitiy of the superior cervical vertebrae, a hydroce phalus or arachnoid cyst of the posterior fossa are often present in this c ontext. Previous theories of the origin and the mechanism of syringomyelia progression have been controversly proposed. Gardner and colleagues postula ted that the primary event is the incomplete embryonic opening of the outle ts of the fourth ventricle. The fluid arrived in the syrinx along the embry ologically natural route down the central canal. Their hydrodynamic theory states that with each arterial pulse, the outflow of CSF is transmitted fro m the fourth ventricle down to the syrinx via the central canal. Most patie nts have patent fourth ventricle foramina and evidence of communication bet ween the ventricle and the syrinx is rare. Williams then proposed his "cran io-spinal pressure dissociation theory". Significant pressure differential occure daily during activities that increase intrathoracic pressure such as sneezing, coughing and could be transmitted to the spinal fluid from the e pidural spinal veins. The progression of the cavity is better understood an d analyzed with dynamic MR imaging and quantitative analysis. The CSF flow from the cranial to the spinal subarachnoid space results fi om the expansi le motion of the brain during the cardiac cycle. The progression of the cav ity is based on pressure acting on the surface of the cord and does nor req uire any communication of the fourth ventricle with the central canal and t he syrinx. The origin of fluid cavity remain questionable. Aboulker but als o Ball and Dayan pointed out the role of the perivascular spaces and the DR EZ which are involved in the communication between the perimedullar CSF, th e spinal cord extracellular spaces and the central canal. Other causes of syringomylia include acquired conditions which could be gro uped under the heading of "non-hindbrain related syringomyelia". Arachnoid scarring is related in many case to spinal trauma or occurs after spinal me ningitis, spinal intradural surgery, peridural anesthesia, subarachnoid hem orrhage. Rarely an extra medullary compression is discussed. The mechanism involved is here again an alteration of the CSF flow at the spinal level.