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Neuromonitoring of Cerebral Aneurysm Coiling: A Case Review

If you’re interested in intraoperative neuromonitoring (IONM) technology, you likely already have an idea of what procedural and technological roles IONM can play in a successful surgery or procedure. We’ve put together a case study detailing – from diagnosis to recovery – a specific circumstance in which intraoperative neuromonitoring technology was integral to a patient’s treatment.


The patient was a 68-year-old woman who experienced shortness of breath over the course of several days, a symptom which emerged leading up to a scheduled atrial fibrillation. Once admitted, she underwent a cardiac catheterization and afterward developed a right facial droop. An MRI was conducted to determine the cause and it was discovered that the patient suffered a middle cerebral artery cerebrovascular accident (or MCA CVA, a type of stroke). The cause of the stroke was determined through the usage of a computed tomography (CT) angiogram, which revealed a 9-millimeter aneurysm in the patient’s right clinoidal segment.

Following a short recovery period for the weakness on her right side, the patient was treated for her aneurysm at the neurovascular lab, with intraoperative neuromonitoring provided by Medsurant.  The procedure included aneurysm coiling, a technique designed to block blood flow into the weakened area of the artery. It was determined that the IONM professional on the team would need to monitor three modalities during the procedure; an electroencephalogram (EEG), a somatosensory evoked potential (SSEP), and an auditory brainstem response (ABR).

An EEG is a typically non-invasive method by which an IONM provider can record the electrical activity of the brain. Although recordings are typically taken by electrodes attached to the patient’s scalp, invasive electrodes are sometimes used in what is referred to as an intracranial electroencephalography (iEEG). In either case, the electrodes are connected to a differential amplifier which amplifies the received signal before passing it to an analog-to-digital converter and then to an anti-aliasing filter. This combination of tools allows the signal to be stored and displayed electronically.

SSEP tests also measure the electrical activity of the brain, but their focus is wholly on the activity that results from the stimulation of touch. Though there are a variety of methods by which stimuli of that nature can be delivered, the most common method is via electrodes that apply electrical stimulation to the skin covering the nerves of the affected limb(s).

Likewise, the body’s response to an ABR is also measured through electrodes attached to a patient’s scalp. An ABR, however, also entails the use of earphones placed just inside the outer canal of the ear, which exposes the patient to a series of sounds. As those sounds occur, the display equipment records the degree to which the patient’s auditory nerves respond.

Included below are the baseline readings from each test as taken before the procedure and what they indicated.


SSEP Baseline

These readings measure the activity of the bilateral median (MN) and posterior tibial nerves (PTN). From studying them, the IONM provider was able to determine that the amplitude of the patient’s right N20 response was smaller than that of her left N20 response.


EEG Baseline

From these readings, the IONM provider could see that the amplitude of the left hemisphere of the patient’s brain was lower than that of her right hemisphere.


ABR Baseline

The ABR indicated similar baseline readings for both the left and right hemispheres of the patient’s brain.



The patient’s brain and nerve activity were monitored continually via SSEPs, ABRs, and EEG  during the procedure; below, we’ve included images of said tests as they appeared approximately nine hours and twenty-one minutes into the surgery, which is when the surgeon began advancing the clotting wire to the patient’s aneurysm.



These measurements indicate a 90% reduction in the amplitude of the left N20 lobe and a slight reduction in the amplitude of the left P37 lobe.


From these results, the IONM technician could determine that a reduction in right hemisphere amplitude and alpha activity had occurred.



No significant differences occurred between the baseline ABR readings and those taken mid-procedure.

When the surgeon found a clot in the patient’s right M2 lobe, they initiated heparin treatment in order to bring activated clotting time (ACT) above 200 seconds. Once that was achieved, they executed retrieval of the clot with a Trevo wire. On the left, we see the identification of the clot; on the right, the insertion of the wire.


The effects of the procedure were quickly seen on both the SSEP and the EEG. Below is an image of the SSEP test as taken less than five minutes after the retrieval of the clot, results which show the recovery of both the left N20 and P37 lobes.

Approximately twenty-five minutes later, the SSEP (as seen below) indicated continued recovery of the amplitude of both lobes.

The below EEG image, meanwhile, taken shortly after clot retrieval indicated the recovery of amplitude and an increase in alpha activity for the right hemisphere of the patient’s brain.

As with the SSEP, the EEG as taken twenty-five minutes later illustrated the continued recovery of the right hemisphere’s amplitude and alpha activity.


Ten hours into the surgery, the angiogram indicated that the clot had been completely removed. The surgeon chose to treat the aneurysm itself at a later date and the patient awoke from the procedure with no new neurological issues.

This operation would not have been as successful if it were not for the use of IONM technology and for the talented provider who monitored the case. Their technical knowledge allowed them to give the surgical team real-time updates on the patient’s neurological condition, indispensable information that gave the surgeon near-instant confirmation that the procedure had been a success. By the same token, the IONM provider would have been able to inform the surgeon at once of any irregularities or issues had the procedure not gone as planned, which would have given the surgical team the opportunity to correct said issues before permanent damage to the patient’s neurological functions resulted.

The above case study is but one of the countless procedures in which intraoperative neuromonitoring technology and equipment provide positive value and an indispensable part of a successful outcome. Medsurant hopes that this case gives you a clearer idea of how you, as an IONM professional, can contribute to the execution of a successful operation. If you have any other questions about the role of IONM technology or professional careers in this growing field, please feel free to contact one of our knowledgeable and friendly representatives.

If you think that you’re ready to invest or learn more about IONM technology and solutions for your facility or team, we welcome you to visit our IONM technology page to learn more about our technology and about the benefits of partnering with Medsurant Health.

Medsurant announces partnership agreement with Capstone Health Alliance

West Conshohocken, Pennsylvania, January 19, 2017 – Medsurant, leading provider of high quality clinical services, and Capstone Health Alliance, regional group purchasing organization of Asheville, North Carolina, are proud to announce their recent partnership agreement in the Intraoperative Neuromonitoring (IONM) service line. Continue reading “Medsurant announces partnership agreement with Capstone Health Alliance” »