Chiari Malformations Abstract VI

Trivial Degrees of Tonsillar Ectopia May be Symptomatic

Dan S. Heffez, M.D.; Jack D. Clemis, M.D.; Dean A. Elias, M.D.; Michael A. Mikhael, M.D. and Leonard J. Cerullo, M.D.; Chicago, Illinois

OBJECTIVE: Cerebellar Tonsillar ectopia is considered of clinical significance only when both tonsils are herniated at least 3mm below the foramen magnum. This criterion is too restrictive.

METHODS: We have evaluated 25 patients with symptoms of cervicomedullary compression in whom the MRI scans showed less than 3mm of tonsillar ectopia. The most common complaints were headache (23/25), nausea (19/25), vertigo (18/25), and gait instability (18/25). The duration of symptoms ranged from 6 weeks to 11 years. Physical findings included an intolerance of neck extension (21/25 patients), dysmetria (15/25), positive Romberg sign (12/25) and occipital tenderness (11/13). The mean tonsillar ectopia was only 0.49mm below the inferior rim of the foramen magnum. Supplemental axial MRI images obtained through the plane of the foramen magnum demonstrated crowding of the neuroanatomical structures to advantage in every case.

RESULTS: One month following decompressive craniectomy with or without duraplasty, 22/24 treated patients had shown an improvement in all symptoms. One patient has refused treatment and 2 are still pending follow-up. After a mean follow-up of 11.94 months, 7 patients remain asymptomatic, 14 patients are improved with resolution of neurological signs despite some mild recurrent or residual symptoms, and 1 patient has severe dizziness.

CONCLUSION: We conclude that even minimal tonsillar ectopia can be symptomatic and that surgical decompression of the foramen magnum can be beneficial. The clinical significance of tonsillar ectopia should be determined by the crowding of the contents of the foramen magnum rather than simply by a measure of tonsillar descent.

Presented at 75 Years of Neurosurgery in Canada 1923-1998, October 28-31, 1998, in Toronto, Ontario, Canada.