False-Negative Motor-Evoked Potential Due to Contrast-Induced Encephalopathy During Coil Embolization for Intracranial Aneurysm: A Case Report.

Contrast-induced encephalopathy (CIE) is a rare neurological complication that can occur following the use of contrast media during angiographic procedures. It can lead to neurological deficits, such as motor weakness. Transcranial motor-evoked potential (TcMEP) monitoring is commonly used to detect pyramidal tract disorders during embolization for intracranial aneurysms. However, it remains unclear whether TcMEP monitoring is effective in cases of motor weakness associated with CIE. We present a case of a false-negative motor-evoked potential caused by CIE during coil embolization for unruptured internal carotid artery aneurysms. A 68-year-old woman with dizziness underwent an MRI, which revealed multiple unruptured cerebral aneurysms, including a right anterior choroidal artery aneurysm (Ach AAn) and a posterior communicating artery aneurysm (Pcom AAn). Coil embolization was performed for the right Ach AAn and Pcom AAn with intraoperative TcMEP monitoring under general anesthesia. Throughout the procedure, no abnormalities were detected in the TcMEP monitoring. A total of 360 mL of contrast medium was used. After regaining consciousness, the patient experienced left hemiplegia and unilateral spatial neglect. Cerebral angiography revealed no missing branches, including those of the Ach A and Pcom A. MRI showed no acute ischemic or hemorrhagic changes. However, CT revealed CIE. The left hemiplegia and unilateral spatial neglect gradually improved and were completely resolved by postoperative day four. This case suggests that CIE-associated motor weakness may not be detected by intraoperative TcMEP monitoring. Therefore, in patients who develop motor weakness immediately after coil embolization for intracranial aneurysms without changes in TcMEP, brain CT should be performed to exclude CIE.