Evaluation of an intracranial arachnoid cyst with MEG after magnetic stimulation.

A 34-year-old male diagnosed of an intracranial arachnoid cyst arising in the left-sided temporal-parietal area, by computed tomography (CT), underwent evaluation by means of MEG. Biomagnetic waveform recordings were obtained from the target area and the Fourier analysis of these measurements was carried out. External magnetic stimulation in the order of pico Tesla was applied with proper field characteristics (intensity: 1-7.5 pT, frequency: 8-13 Hz), which were obtained prior to the application and the emitted MEG activity was recorded again. The cortical area adjacent to the borders of the arachnoid cyst emitted biomagnetic waveforms with high values. The application of magnetic stimulation resulted in a rapid attenuation of the high MEG activity in the target area. MEG may provide useful information in the diagnostic evaluation of arachnoid cyst patients and could be a supplement to other imaging modalities.