Purpose: The pattern-reversal visual evoked potential measured electrically from scalp electrodes is known to be decreased, or absent, in patients with occipital lobe lesions. We questioned whether the measurement and source analysis of the neuromagnetic visual evoked field (VEF) might offer additional information regarding visual cortex relative to the occipital lesion.
Methods: We retrospectively examined 12 children (6-18 years) with occipital lesions on MRI, who underwent magnetoencephalography and ophthalmology as part of their presurgical assessment. Binocular half-field pattern-reversal VEFs were obtained in a 151-channel whole-head magnetoencephalography. Data were averaged and dipole source analyses were performed for each half-field stimulation.
Results: A significant lateral shift (P < 0.02) in the dipole location was observed in the lesional hemisphere compared with those in the nonlesional hemisphere, regardless of the lesion location. No differences were observed in latency, strength (moment), and residual errors of VEF dipoles between the lesional and nonlesional hemispheres.
Conclusions: Magnetoencephalography demonstrated the mass effect on the dipole location of VEF in children with occipital lesions. Magnetoencephalography may be useful as a screening test of visual function in young patients. We discuss potential explanations for this lateral shift and emphasize the utility of adding the magnetoencephalography pattern-reversal visual evoked field protocol to the neurologic work-up.