OBJECTIVE: To determine if slight descent of the cerebellar tonsils (< 5 mm below the foramen magnum; tonsillar ectopia) may cause surgically treatable symptomatology. METHODS: A consecutive series of nine symptomatic patients with tonsillar ectopia seen between December 1990 and March 1993 are reported on. The same number of age and sex matched controls were selected at random from outpatients. Twelve asymptomatic subjects with tonsillar ectopia were found among 5000 people between January 1991 and March 1996. Diagnosis of tonsillar ectopia was based on midsagittal MRI. RESULTS: Patients presented mainly with chronic intractable occipital dull pain, vertigo, and dysequilibrium. In all patients MRI showed normal brain structure except for tonsillar ectopia (-2.9 (SD 0.8) mm), which has historically been thought to be of no clinical relevance. In the control group the tonsilar position was +2.1 (SD 2.8) mm (p<0.01). Neurotologically abnormal findings were detected with a monaural speech integration test (100%), eye tracking test (56%), optokinetic nystagmus test (89%), and visual suppression test (67%) which strongly suggested a CNS lesion. In accordance with the results of MRI and precise neurotological examination, posterior fossa decompression surgery was carried out, followed by improvement of preoperative symptoms and less severity of neurotological abnormalities in all patients. CONCLUSION: Tonsillar ectopia could cause neurological symptoms in small populations, which were surgically treatable. Neurotological assessment was necessary to verify the aetiological relation between tonsillar ectopia and various symptoms.
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