Sphenoidal electrode positions and basal EEG during long term monitoring.

In 33 patients undergoing extended EEG monitoring, stereoscopic basal skull radiographs demonstrated the positions of Teflon-coated, 40-gauge, multistranded, silver wire electrodes shortly after their insertion and just before their removal an average of 5.12 days later. Although the electrodes had been firmly secured to the skin with plastic surgical adhesive tape and there was no evidence that they had been manually pulled out, many wee kinked and relatively superficially situated at the end, compared with the onset, of each monitoring period. Electrodes moved similar amounts bilaterally and migrated further as the days passed. Sphenoidal wire tips that had been an average of 7.02 mm lateral to the foramen ovale when placed eventually averaged 15.79 mm from this landmark. There was no relationship between distance moved by the electrodes and sex, age, or number or type of seizures exhibited. Review of EEG records of interictal discharges and seizures revealed no differences attributable to the relative electrode positions.