Method

Parotidectomy

Parotidectomy is the partial or complete removal of the parotid gland. The most frequent indications for parotidectomy are benign or malignant tumours, and in rarer cases also infectious diseases of the parotid gland.^[1]

Importance of neuromonitoring during parotidectomy

Depending on the extent of the parotidectomy, the branches of the facial nerve (which fan out through the parotid gland in a path which varies between individuals), are in or near the surgical field. These branches can be affected by tension, pressure or other manipulation. Injury to the facial nerve during parotidectomy can lead to temporary or permanent paresis or paralysis of the mimic muscles.

Localisation and functional monitoring of the facial nerve by intraoperative neuromonitoring has already been established for several years in ENT surgery, for example in parotidectomy, thanks to the advantages it offers for patient protection. If the tumour has infiltrated the facial nerve, it is often not possible to perform a nerve-sparing surgery in the course of a radical parotidectomy.

Neuromonitoring method during parotidectomy for monitoring the facial nerve

Please note that the following recommendations on neuromonitoring during parotidectomy are of a general nature. The individual vital parameters of the patients, the existing surgical situation and the technology used should always be considered.

>> An extensive electromyographic recording (EMG) of the mimic muscles requires 2 to 4 recording channels. One pair of electrodes is required per channel. It is recommended to place the two needles of a pair of electrodes at a distance of approximately 0.5 to 1 cm from each other in the same muscle. The ground electrode should be placed in the contralateral soft tissue.

>> Bipolar and monopolar stimulation probes can be used to stimulate the branches of the facial nerve during parotidectomy. This enables the localisation and functional monitoring of the nerve.

>> Monopolar stimulations should be performed at least 5 cm away from the recording electrodes.

>> To trigger a stimulus response during parotidectomy, the stimulation must exceed the motor threshold.

>> The lower the current intensity, the more selectively the nerve can be identified.

>> The muscle contraction caused by the stimulation is displayed acoustically and visually via the recording electrodes on a monitoring device as an EMG response. This allows the surgeons to adjust their surgical approach during the parotidectomy if necessary.

In addition to parotidectomy, EMG montoring is also used in proctology for complex nerve structures.

References

1. Bova, R.; Saylor, A.; Coman, W. B. Parotidectomy: review of treatment and outcomes: ANZ journal of surgery. pp. 563–568 (2004).

Aage R. Møller, Intraoperative neurophysiological monitoring, 2nd ed. Totowa, N.J: Humana Press, pp. 205–206 (2006).

Nuwer, M. Handbook of Clinical Neurophysiology, Volume 8, Intraoperative Monitoring of neural Function, Chapter 25, Intraoperative facial nerve monitoring (2008).