SAN FRANCISCO – Intraoperative neurophysiologic monitoring techniques may require modification for moyamoya disease because of a lack of sensitivity for new strokes, according to a retrospective study of 700 moyamoya revascularization cases.
The monitoring caught only 4 of 29 new strokes during procedures on 435 patients, said Dr. Viet Nguyen, a neurologist at Stanford (Calif.) University.
Dr. Viet Nguyen
Intraoperative neurophysiologic monitoring (IONM) can help detect ischemia or hemorrhage during procedures in which patients cannot communicate sensations like numbness and tingling. But until now, no one had specifically examined how well it works in surgery for moyamoya disease.
Dr. Nguyen and his colleagues studied the effectiveness of IONM that was performed during superficial temporal artery–middle cerebral artery anastomosis or encephaloduroarteriosynangiosis.
For the monitoring, the researchers used bilateral upper-extremity somatosensory-evoked potentials (SSEPs) and eight-lead parasagittal scalp EEG.
They recorded postoperative events, including new strokes, new hemorrhages within the first postoperative day, and transient neurological events. They defined transient neurological events as postoperative symptoms that lasted longer than 24 hours but resolved completely and without new infarcts on MRI.
They defined permanent IONM changes as those that lasted through the end of monitoring. Transient IONM changes were those that resolved during the monitoring.
Three of the cases had intracerebral hemorrhage in the first postoperative day, but only one of these incidents caused a change in the IONM.
Transient IONM changes occurred in 19 cases. Most of these were speech or facial deficits that fluctuated over days without correlating infarcts detected by imaging. The IONM picked up a change in only one of these incidents.
These findings led the investigators to conclude that IONM is not adequately sensitive in moyamoya surgery.
On the other hand, the monitoring had 100% specificity.
"If we saw a permanent change, it indicated something bad was going to happen," Dr. Nguyen said.
Each of the four permanent changes they recorded was correlated with a serious event (three strokes and a hemorrhage). In contrast, only 2 of the 19 temporary IONM changes correlated with a postoperative event. These included one stroke and one transient neurological event.
One reason for the reduced sensitivity might be the difficulty of placing electrodes properly around the surgical site. Also, the criterion that was used to define an official drop in SSEPs – a decrease in the amplitude to less than 50% of baseline levels – might have been too high to detect mild ischemia. The surgeons’ interventions, such as increasing the median arterial pressure or unocclusion of the middle cerebral artery (MCA) distal branch following anastomosis to an extracranial artery, also might have reversed the IONM change while also averting a pending infarction, the investigators concluded.
The researchers had expected that the events would mostly come during the occlusion of the MCA, but they found that the IONM changes could occur during any part of the case. "We found that [occluding the MCA] was not the riskiest part of the procedure," Dr. Nguyen said.
He suggested that future research should include monitoring for ischemic changes in a broader territory, not just the area around the site of the procedure.
None of the investigators had relevant disclosures.