Monitoring of visual-evoked potentials during fat packing in endoscopic resection of a giant pituitary adenoma.

Background: Endoscopic transsphenoidal surgery has become a mainstay surgical approach for sellar pathologies and can effectively decompress mass effects on the optic nerves. Visual-evoked potentials (VEPs) have been utilized as an intraoperative adjunct during endoscopic transsphenoidal surgery to monitor the integrity of the optic pathways, but the data surrounding its reliability and efficacy remain heterogeneous.

Case Description: An 80-year-old male underwent endoscopic transsphenoidal resection of a pituitary macroadenoma with preoperative visual deficits related to optic nerve compression. During fat packing of the resection cavity, a decrease in VEPs was noted, which seemingly improved after partial fat removal, although with paradoxically reduced VEP latencies. Despite this, the patient developed a visual field deficit postoperatively, requiring re-operation for further removal of the fat packing.

Conclusion: This was a case of initially poorly formed VEPs that deteriorated and apparently improved following surgical intervention. The finding of shortened latencies of the VEPs was likely from noise contamination, creating the illusion of improved signal amplitudes. We recommend careful assessment of VEP data for baseline reproducibility, particularly in patients with pre-existing visual field deficits. Appropriate anesthetic selection is also important to reduce noise interference from the electroencephalogram.