A novel simple real-time electrooculographic monitoring system during transsphenoidal surgeries to prevent postoperative extraocular motor nerve dysfunction

In transsphenoidal surgery (TSS) for pituitary tumors, the use of endoscopes allows approach to the lateral sides in and around the cavernous sinus. However, this approach is often associated with a risk of cranial nerve dysfunction causing impaired extraocular movement. We employed a novel, simple, and real-time monitoring system using electrooculography during TSS to avoid postoperative extraocular motor nerve dysfunction. A conventional electroencephalograph, which is available in every hospital, was used to detect effects induced by intraoperative manipulation on the cranial nerves related to extraocular movement (EOM) during TSS for pituitary adenomas. One hundred patients with pituitary adenomas who underwent endonasal endoscope-assisted TSS with EOM monitoring were included in the present study. When the extraocular motor nerves were stimulated mechanically directly or even indirectly by surgical procedures, abnormal extraocular muscle responses [electrooculograms (EOGm)] appeared on the monitor screen. When repeated or continuous EOGm were recorded, surgical procedures were discontinued briefly for around 5 to 10 s. The EOGm disappeared promptly when surgical procedures were stopped. Permanent extraocular dysfunction did not occur in the present series of patients. One, who was the fifth patient in the present series, of 100 patients (1.0 %) had transient delayed diplopia after TSS. We have not experienced any more postoperative EOM dysfunction since the first case. EOM monitoring during TSS is a novel, efficient, and simple method to prevent postoperative cranial nerve palsy related to EOM.