Craniovertebral Junction Abnormalities with Hindbrain Herniation and Syringomyelia: Regression of Syringomyelia After Excision of Ventral Craniovertebral Compression

Summary

The hindbrain herniation syndrome occurs frequently with craniovertebral junction (CVJ) abnormalities that reduce posterior fossa volume. Syringohydromyelia (SHM) is often present. Posterior fossa dorsal decompression (PFD) is customary, but has an adverse outcome when ventral bony abnormality exists in these circumstances. The results of a prospective study on CVJ abnormalities with Chiari malformation I (CM1) and SHM are presented. Between 1984 and 1999 (MRI era), 428 patients aged 6–68 years underwent operation for CM1; 154 had ventral CV abnormalities; 44 had associated SHM. Twelve had bone softening states with secondary basilar impression (6 previous PFD and 6 fusions); 26 had primary basilar invagination (10 had PFD, 9 previous syrinx-subarachnoid shunts and syrinx to peritoneal shunts). Symptoms reflected brainstem and high cervical myelopathy and cranial nerve deficits. Neurodiagnostic imaging included CT and MRI in dynamic modes and cine flow studies. All 44 patients had irreducible ventral CVJ bony invagination and underwent transpalatopharyngeal decompression of the cervicomedullary junction and dorsal occipitocervical fusion. Cervicothoracic SHM was present in 30, thoracic in 6, and holocord in 6. Brainstem symptoms regressed in 36 of the 44 patients; myelopathy regressed in 38 of 44 patients; and SHM showed MRI resolution in 34 of 44. Neurological improvement and SHM resolution can occur with ventral cervicomedullary junction decompression in patients with basilar invagination and basilar impression, likely because of relief of the neural encroachment and reestablishment of CSF pathways.