Past studies have suggested that tumor resection might lead to fewer postoperative visual field defects if surgeons monitor the posterior visual pathway during the procedure. This study evaluated the value of intraoperative navigation using MRI-based tractography and electrophysiological monitoring of the visual pathways during awake craniotomy.

Study design

The authors retrospectively analyzed data collected from 18 patients who underwent an awake craniotomy for resection of intra-axial tumors involving, or adjacent to, the optic radiations. During the craniotomy, MRI-based tractography, direct cortical visual evoked potentials, subcortical recordings from the optic radiations, and subcortical stimulation of the optic radiations were used to assess visual function and proximity of the lesion to the optic radiations. Visual fields were assessed before and after the surgery.

Outcomes

No association was found between preoperative visual field status and baseline presence of cortical visual evoked potentials. Five of 14 patients who underwent subcortical stimulation of the optic radiations reported seeing phosphenes in their corresponding contralateral visual fields.

There was a positive correlation between the subcortical threshold stimulation intensity and the distance from the optic radiations. Subcortical recordings from the optic radiations were present only when recordings were obtained within 10 mm of the optic radiations. Seven patients had postoperative visual field deterioration, which was associated with a length of less than 8 mm between the tumor and the optic radiations.

Limitations

The authors conclude that intraoperative electrophysiological monitoring of the visual pathways is feasible, but may be of limited value in preserving the functional integrity of the posterior visual pathways. Subcortical stimulation of the optic radiations intraoperatively may identify the location of the optic radiations when done in proximity to the pathways, but such proximity could potentially cause visual field defects to worsen after surgery.

Clinical significance

It is possible that intraoperative monitoring of the visual pathways during neurosurgical resection of tumors may be able to limit damage to the visual system, resulting in less visual field loss.