Cranial Nerve Monitoring… Continued

In the last post, Cranial and Peripheral Nerve Monitoring – Clinical Uses Part 1, I went over a scenario were an unanticipated postoperative problem occurred due to poor neuromonitoring. The SNP’s feedback led the surgeon to believe the opposite what was true. It doesn’t matter of your doing peripheral cranial nerve monitoring or central cord monitoring, poor neuromonitoring is probably worse than no monitoring at all.

Now back to our story…


cranial nerve monitoring

Image from


Scratching your head, you figure out that today wasn’t the shining moment in your IOM career. Here’s what you had to offer:

  1. False negative EMG on the first side, since the nerve was cut and you didn’t get any activity.
  2. False positive tEMG on the first and second sides (ok, debate if you want to label this as a real false positive or not since he didn’t stimulate the whole nerve), since the surgeon only stimulated distal to the lesion to get a response.
  3. True positive EMG on the second side, since the patient woke up with an injury on that side.

Even though your EMG was correct on the second side, it missed the severing of the nerve on the first side. And in this case, we aren’t sure as to what extent it helped in preventing injury. For the second side, we’ll never know if it was the initial insult, the second, or a compounding effect. EMG does a poor job at qualifying the extent of the injury.

You also realize that the disappearance of train EMG and stimulating the portion of the nerve distal to the operative site offers poor clinical data.

What’s The Peripheral and Cranial Nerve Monitoring Lesson Learned?

It’s very likely that the surgeon severed the nerve on the first side, and there was not enough activity for the EMG to pick up a response (reports of this are seen in the literature as well). So if the surgeon stimulated proximal and distal to the nerve on the first side, he would have realized that the nerve was severed completely.

The surgeon might not have risked injury to the other nerve since vocal paresis is not as detrimental as vocal paralysis. He might have second guessed his opinion to aggressively remove the tumor on the second side with a severed nerve on the other and train EMG  on the second side. But again, this is all hypothetical.

Also, if the surgeon used the probe to trace the nerve better, he might have found out some other useful info. He might have been able to map it out better, and prevented the nerve injury altogether.

While I made this whole scenario up, it’s not far fetched to find yourself in this very predicament. The best way to handle something like this is to prevent it before it happens in the first place.

  1. Let the surgeon know what the best stimulating techniques are for identifying a cranial nerve.
  2. Talk during the surgery so you can better interpret your free-running EMG by knowing what the surgeon is doing.
  3. Inform the surgeon to strengths and weaknesses of your modalities.
  4. Be better than the automated system.

Anyone else ever have a case similar while performing cranial nerve monitoring? What was done differently, or the same?


Here’s a nice anatomy lesson of the recurrent laryngeal nerve during a thyroidectomy…



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Joe Hartman DC, DACNB, DABNM

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