Introduction: Since the introduction of MRI, the incidence of Chiari I malformations (cerebellar tonsils ectopia) has increased. The clinical significance of this finding remains questionable in some instances. Recently, cine flow MRI has added to the understanding of the dynamics of cerebrospinal fluid at the craniocervical junction and to the pathophysiology of the Chiari I malformation. The present study attempts to analyze the role of cine flow MRI in Chiari I malformations.
Materials and methods: Between January 1990 and December 2000, 24 patients were identified who met the following inclusion criteria: patients diagnosed with Chiari I malformation who had had an MRI of the brain including the craniocervical junction, clinical follow-up for at least six months, and cine flow studies had to have been performed pre- and postoperatively. The cine flow studies were repeated during follow-up if the patients were not surgical candidates. Patients harboring intracranial space occupying lesions or lumboperitoneal shunts were excluded. Sixteen of the 24 selected patients underwent 18 operations and 8 were followed conservatively. There was a wide variation in clinical presentations. Twelve patients had cerebellar tonsils protruding more than 5 mm below the foramen magnum, and in 12 patients the descent of the cerebellar tonsils was less than 5 mm. Despite this difference in the degree of protrusion, there was no significant difference in clinical presentation. The cisterna magna was small or absent in 20 patients with sluggish cine flow posteriorly, 19 of whom were symptomatic, in contrast to 1 symptomatic patient who had satisfactory cine flow.
Results: All patients with Chiari I malformation and an associated cervical syrinx had absent cine flow at the craniovertebral junction, and this finding was statistically significant. There was a good correlation between the clinical presentation and cine flow preoperatively, and between clinical improvement and cine flow postoperatively. Patients with Chiari I malformation, cervical syrinx, and absent cine flow preoperatively improved after suboccipital decompression and duroplasty. Patients with Chiari I malformations without syrinx and absent cine flow underwent suboccipital bony decompression alone and had satisfactory outcomes.