Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils

Abstract

The mechanisms previously proposed for the progression of syringomyelia associated with Chiari I malformation of the cerebellar tonsils are controversial, leave many clinical observations unexplained, and underlie the prevalence of different operations currently used as initial treatment. To explore the mechanism of syringomyelia progression in this setting, the authors used anatomical and dynamic (phase-contrast and phase-contrast cine) magnetic resonance (MR) imaging, and intraoperative ultrasonography to examine the anatomy and dynamics of movement of the cerebellar tonsils, the wall of the spinal cord surrounding the syrinx, and the movement of cerebrospinal fluid (CSF) and syrinx fluid at rest, during the respiratory and cardiac cycles, and during Valsalva maneuver in seven affected patients. In all patients the cerebellar tonsils occluded the subarachnoid space at the level of the foramen magnum. Syringomyelia extended from the cervical to the lower thoracic segment of the spinal cord. No patient had evidence of a patent communication between the fourth ventricle and the syrinx on anatomical MR images, dynamic MR images, or intraoperative ultrasound studies. Dynamic MR images of three patients revealed abrupt downward movement of the spinal CSF and the syrinx fluid during systole and upward movement during diastole, but limited movement of CSF across the foramen magnum during the cardiac cycle. Intraoperative ultrasound studies demonstrated abrupt downward movement of the cerebellar tonsils during systole that was synchronous with sudden constriction of the spinal cord and syrinx. Decompression of the foramen magnum was achieved via suboccipital craniectomy, laminectomy of C-1 and C-2, and dural grafting, leaving the arachnoid intact. Immediately after surgery, the pulsatile downward thrust of the tonsils and constriction of the spinal cord and syrinx disappeared. Syringomyelia resolved within 1 to 6 months after surgery in all patients. Observations by the authors suggest the following previously unrecognized mechanism for progression of syringomyelia associated with occlusion of the subarachnoid space at the foramen magnum. The brain expands as it fills with blood during systole, imparting a systolic pressure wave to the intracranial CSF that is accommodated in normal subjects by sudden movement of CSF from the basal cisterns to the upper portion of the spinal canal. With obstruction to rapid movement of CSF at the foramen magnum, the cerebellar tonsils, which plug the subarachnoid space posteriorly, move downward with each systolic pulse, acting as a piston on the partially isolated spinal CSF and producing a systolic pressure wave in the spinal CSF that acts on the surface of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Chiari I malformation associated with syringomyelia: a retrospective study of 316 surgically treated patients

“…Gardner and Angel 3 believe that the water-hammer effect brought about by pressure waves coming from the choroid plexuses is transmitted to the CSF causing an enlargement of the central canal of the spinal cord. Oldfield et al 4 proposed that the formation of syringomyelia might result from downward migration of the tonsils, producing a systolic pressure wave, which acts on the surface of the spinal cord like pistons. Williams 5 takes the gradient that exists between the intracranial and the intraspinal pressure as the cause of syringomyelic cavitation.…”

“…4,[7][8][9] It involves removing bone in the suboccipital area along with the posterior margin of the foramen magnum Group I D A 128 66 37 20 5 Group II D+SS B 39 20 11 6 2 Group III D+T C 106 55 31 16 4 Group IV D+T+SS D 43 22 13 7 1 Abbreviations: CMI, Chiari I malformation; D, suboccipital decompression; MRI, magnetic resonance imaging; SS, syringosubarachnoid shunt; T, cerebellar tonsillectomy. Figure 1 Preoperative MRI scan of a patient with syringomyelia associated with CMI illustrating a prominent syrinx (arrow).…”

Surgical management of syringomyelia-Chiari complex

“…However, there are no objective criteria to suggest which procedure will produce the best surgical results in such cases, and comparisons are difficult because of the differences in surgical techniques, indications for operation, and criteria for the evaluation of results, including length of follow-up period. It should be pointed out that in the most successful surgical series, posterior fossa decompression relieves the symptoms of syringomyelia in only 50% of the cases [1,18,20]. The other group of authors have advocated syrinx shunting procedures as the initial approach, as they are easy to perform, are generally well tolerated and are associated with results that are easily the equal of those achieved by foramen magnum decompression [2][3][4].…”

Syringomyelia and Arnold Chiari in scoliosis initially classified as idiopathic: Experience with 25 patients

“…In some papers, the authors distinguish between "paralytic scoliosis" and "idiopathic scoliosis" ]1, 8,11,15]. "Paralytic scoliosis" is observed with severe dysraphism in children and it is always a very evolutive scoliosis.…”