Hindbrain herniation syndrome, or Chiari malformation Type I (CM-I), occurs frequently with craniovertebral junction (CVJ) abnormalities when there is reduction in the posterior fossa volume. Syringomyelia is often present. Posterior fossa dorsal decompression (PFDD) is typically performed but has adverse results when ventral bone abnormality exists. This paper presents the results of a prospective study on CVJ abnormalities in patients with CM-I and syringomyelia.
Between 1984 and 2008 (the MR imaging era), 298 patients with CVJ abnormalities and CM-I underwent ventral cervicomedullary decompression. Eighty-four patients had associated syringomyelia (15 with secondary invagination and 69 with primary basilar invagination, os odontoideum, or malunion of fractures). Of these 84 patients with CVJ abnormalities, CM-I, and syringomyelia, 46 had previously undergone PFDD, and 28 had previously undergone PFDD combined with fusion procedures or shunt placements. Of the 84 patients, a cervicothoracic syrinx was observed in 57, thoracic syrinx in 14, and holocord syrinx in 13. Studies included CT, MR imaging, and cine flow studies. All 298 patients who underwent ventral CVJ decompression had irreducible or partially reducible pathology. All 84 with syringomyelia showed brainstem dysfunction, lower cranial nerve symptoms, or myelopathy.
Brainstem signs improved in 66 of the 84 patients, myelopathy improved in 58, and syringomyelia regressed in 64.
Neurological improvement and syringomyelia resolution can occur using only ventral cervicomedullary junction decompression in patients with basilar invagination and basilar impression. This is likely due to the relief of neural encroachment and reestablishment of CSF pathways.