Arnold-Chiari Complex.

Syringomyelia is frequently accompanied by an extramedullary lesion at the foramen magnum, particularly a Chiari I malformation. Although syringomyelia associated with foramen magnum obstruction has characteristic clinical, radiological, and neuropathological features, its pathogenesis remains unclear. Currently prevalent hydrodynamical theories assert that obstruction of the subarachnoid space at the foramen magnum interferes with flow of cerebrospinal fluid (CSF) between the spinal and the intracranial subarachnoid compartments. As a result, spinal CSF is driven into the spinal cord through the perivascular spaces to form a syrinx. These theories are implausible biophysically because none postulates a pump adequate to drive fluid through these spaces. None of the theories can explain why syrinx pressure is higher than CSF pressure; why extensive gliosis, edema, and vascular wall thickening regularly occur; and why the composition of syrinx fluid is not identical with that of CSF. A new theory of pathogenesis is proposed to address these difficulties. In the presence of subarachnoid obstruction at the foramen magnum, a variety of activities, such as assuming the erect posture, coughing or straining, and pulsatile fluctuations of CSF pressure during the cardiac cycle, produce transiently higher CSF pressure above the block than below it. There are corresponding changes in transmural venous and capillary pressure favoring dilation of vessels below the block and collapse of vessels above the block. The spatially uneven change of vessel caliber produces mechanical stress on the spinal cord, particularly caudal to the block. The mechanical stress, coupled with venous and capillary dilation, partially disrupt the blood-spinal cord barrier, allowing ultrafiltration of crystalloids and accumulation of a protein-poor fluid. The proposed theory is consistent with the neuropathological findings in syringomyelia and with the pressure and composition of syrinx fluid. It also accounts for the prolonged course of syringomyelia and its aggravation by cough, strain, and assumption of an erect posture. It contributes to understanding the low incidence and the morphology of syringobulbia. It explains the poorly understood presentation of foramen magnum meningiomas with symptoms of a mid- to low-cervical myelopathy. The theory also affords an understanding of the late recurrence of symptoms in children with hydromyelia who are treated with a ventricular shunt.

Arnold-Chiari Malformation↗

PubMed2004

Treatment and management of the Chiari II malformation: an evidence-based review of the literature.

OBJECTIVE: Multiple surgical strategies exist for the management of the symptomatic Chiari II malformation. To date, no comprehensive analysis of this medical literature in an attempt to seek out standards or guidelines has been performed, thus serving as the impetus for this present review. METHODS: A computerized search of the database of the National Library of Medicine was performed on the English-language medical literature between 1966 and 2003. Terms searched for included hindbrain hernia, Chiari II, Arnold-Chiari, surgery, decompression, syringomyelia, and CSF shunts. All literature found was reviewed with associated references from these sources. Each piece of literature reviewed was scrutinized and guidelines developed utilizing the methodology used by the Guidelines for the Management of Acute Cervical Spine and Spinal Cord Injuries. RESULTS: All data reviewed were deemed to be Class III in nature. No standards or guidelines could be established from the available literature. There is significant debate and variable results in the current neurosurgical literature regarding the evaluation of shunt function vs. Chiari II decompression in patients with symptomatic hindbrain herniation. CONCLUSIONS: Multi-institutional prospective randomized trials are needed before any conclusions can be drawn regarding symptomatic Chiari II and its treatment paradigm. Until this time, clinical practice will be based on individual surgeons' experience, training, and personal beliefs.

Arnold-Chiari Malformation↗