Surgical resection of lesions in the temporal lobe carries the risk to visual pathways. Mapping these pathways directly can offer guidance during surgery, reducing the risk of postoperative visual deficits. While intraoperative mapping of motor and language pathways is common, monitoring visual pathways primarily relies on occasional use of visual evoked potentials(VEPs). The direct mapping of visual pathways with subcortical evoked potentials(SCEP) remains an underexplored area, lacking established protocols.

We review cases from 2022-2023 involving temporal lobe resection at a single academic center which required the use of VEPs and SCEPs. VEPs were obtained using flash goggles. SCEPs was obtained with monopolar and bipolar stimulation probes directly over temporal subcortical areas. Potentials were recorded from occipital corkscrew scalp electrodes (O1, O2, Oz). Patients’ preoperative visual deficits, anesthetic agents utilized, and thresholds for evoked potentials are analyzed.

Of the four cases, direct subcortical stimulation evoked responses in two cases. Thresholds for stimulation ranged from 7-8mA. Latencies of the P1 responses ranged from 5.5-9ms. Neither of these patients experienced visual deficits before or after the procedure. One of the cases involved use of inhaled anesthetics (MAC 0.2-0.3). In two cases, both with visual deficits at baseline, direct subcortical stimulation did not elicit evoked potentials.

These cases offer valuable insights into the use of SCEPs for mapping of optic radiations and show possible correlations to patient deficits and anesthetic effects. We also demonstrate reliable acquisition of direct subcortical evoked potentials, even under general anesthesia with intermittent inhaled gas. These cases support continued exploration and implementation of subcortical evoked potentials.