High False-Negative Rate of Intraoperative Neurophysiologic Monitoring in Blood Blister-Like Aneurysm Surgery: Insights from a Retrospective Case Series.

Objective: Surgical management of blood blister-like aneurysm (BBA) is challenging and contentious because of high morbidity and mortality. Intraoperative neurophysiologic monitoring (IONM) is a well-established tool in intracranial aneurysm surgery, although its application in BBA surgery lacks reports. This study retrospectively analyzes the usefulness of IONM in BBA surgery between 2018 and 2023.

Methods: We used somatosensory evoked potentials (SSEPs) and transcranial motor evoked potentials to monitor ischemia during operations. Neurologic outcomes were mainly assessed through daily assessment with the Glasgow Coma Scale, computed tomography within 24 hours, and modified Rankin Scale at discharge.

Results: Thirteen patients with ruptured BBAs (9 Tibetan, 4 Han; 10 women, 3 men; mean age, 55 years) underwent surgical procedures involving 10 clippings (6 direct, 2 wrapping-assisted, and 2 balloon-assisted) and 3 trappings. There were 8 clipping procedures applied for temporary arterial occlusion ranging from 5 to 125 minutes. Irreversible change of SSEPs/transcranial motor evoked potential (tcMEPs) occurred in 3 clippings; all these patients developed postoperative neurologic deficits. Reversible signal change of SSEPs occurred in 3 clippings, with 1 neurologic deficit. As for 3 trapping surgeries, all showed significant deficits regardless of reversible signal change or unchanged signals in IONM.

Conclusions: Our results show that IONM has low sensitivity (37.5%) and high specificity (100%) in detecting ischemic events during BBA surgery. The high rate of false-negative results in BBA-IONM suggests that its predictive value is limited particularly in complex maneuvers such as trapping and advanced vasoreconstruction, warranting cautious interpretation and further investigation of IONM modalities for BBA management.