Objective: To study the outcome of EEG from patients with Chiari I malformations and nonspecific EEG abnormalities, after posterior fossa decompression and CSF flow normalization.
Methods: Three 'apparently asymptomatic' children who had been diagnosed with Arnold-Chiari type 1 EEG abnormalities and who exhibited (a) a wide range of abnormalities according to common anatomical Chiari MRI classifications (Elster AD, Chen MY. Chiari I malformations: clinical and radiologic reappraisal. Radiology 1992;183:347-53), (b) a lack of specific, clinical signs of increased intracranial pressure, and (c) apparently unrelated, EEG-nonspecific abnormalities (focal intermittent rhythmic delta activity (IRDA)--solely in patients 1 and 3, and with focal IRDA plus spikes and spike waves of high voltage in patient 2). Standard EEGs were recorded before surgery and within one month of surgery, which was performed in conjunction with intraoperative echo-Doppler ultrasonography to control CSF flow. Subsequent EEGs and clinical follow-ups were performed within 6-12 months of surgery.
Results: In all patients, intraoperative echo-Doppler ultrasonographic control demonstrated poor CSF flow, which was completely restored by posterior fossa decompression. In all patients, the EEG abnormalities disappeared within one month of surgery and the EEGs were normal at follow-up.
Conclusions: A new CNS symptom, identified as focal IRDA alone or focal IRDA plus spikes and spike waves of high voltage in the EEG, seems to be associated with poor CSF flow in 'apparently asymptomatic' patients with Chiari type I malformations.
Significance: The identified, paroxysmal EEG abnormalities should be interpreted as an indirect sign of subtle CNS distress.