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

Abstract

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.

Keywords: cerebral aneurysm; coil embolization; contrast-induced encephalopathy; false-negative; motor-evoked potential.

Figure 1. Multiple ICA aneurysms on the right side

A right ICA angiogram revealed multiple aneurysms (A and B). Three right ICA aneurysms were identified on 3D rotational angiography, including an Ach AAn and a large Pcom AAn (C and D). White arrows and arrowheads indicate the Ach A and the posterior cerebral artery arising from the Pcom A. Ach Aan, anterior choroidal artery aneurysm; ICA, internal carotid artery; Pcom AAn, posterior communicating artery aneurysm

Figure 2. Intraoperative angiography of the right ICA

Preoperative (A and B) and postoperative (C and D) angiograms during coil embolization of an Ach AAn are shown, with the missing branch not detected. Preoperative (E and F) and postoperative (G and H) angiograms during coil embolization of a Pcom AAn are also shown, with the missing branch not detected. White arrows and arrowheads indicate the Ach A and the posterior cerebral artery arising from the Pcom A. Ach Aan, anterior choroidal artery aneurysm; ICA, internal carotid artery; Pcom AAn, posterior communicating artery aneurysm

Figure 3. TcMEP monitoring throughout the procedure

There was no difference in the MEP wave of the left upper and lower extremities before (A) and after (B) coil embolization of the Ach AAn. Similarly, the MEP wave remained unchanged following coil embolization of the Pcom AAn (C). Ach AAn, anterior choroidal artery aneurysm; MEP, motor-evoked potential; Pcom AAn, posterior communicating artery aneurysm; TcMEP, transcranial motor-evoked potential

Figure 4. Postoperative MRI and CT findings

DWI (A), fluid-attenuated inversion recovery (B), and T2*-weighted imaging (C) revealed no acute ischemic or hemorrhagic changes. Noncontrast CT, performed within one hour after coil embolization, showed cortical and subcortical contrast enhancement in the right cerebral hemisphere (D and E). DWI on postoperative day one (F) showed no ischemic changes. The contrast enhancement in the right cerebral hemisphere on CT completely resolved by postoperative day four (G and H). DWI, diffusion-weighted imaging