[Postoperative normalization of prolonged P100m latency in the visual evoked magnetic field in a patient with occipital meningioma].

A 49-year-old female with a left occipital parasagittal meningioma was found to have prolonged P100m latency of the pattern reversal visual evoked magnetic field only in the hemisphere containing the lesion. After total removal of the tumor, the P100m latency was normalized in the affected hemisphere. Based on current dipole models, all the P100m dipoles were localized at the lateral bottom of the calcarine fissures bilaterally, as indicated by our previous study with normal subjects. Since the tumor was located near the parietoocipital sulcus and distant from the primary visual cortex, disturbance of the higher visual cortex probably affected the P100m latency.