by Neurophysiology Plus Iceland © 2018
IONM in 31 year-old male patient
with 43/41mm right cerebello-pontine angle (CPA) tumor
(e-Bulletin report)
We performed the following
modalities:
Transcranial MEP, Corticogeniculate
MEP (CoMEP), SSEP from both tibialis nerve, EEG, mapping cranial nerves
(accesorius, hypoglossus, glosopharingeal, facialis ), BAEP, TOF, Blink Reflex.
Results: All modalities could be performed with exception of blink
reflex which was not elicited.
Incidents: At the end of the surgery we observed decrement of right
facialis (Orbicular oris muscle), CoMEP
decrement of more than 80% which did not recover throughout the rest of the
surgery. Surgeons explained that "there was a bleeding around the
nerve". They started cooling,
irrigate and "treat" the lesion. Mapping showed also partial decrement, but
recovered after 20 minutes when stimulation was performed proximally.
Our protocol for corticobulbar
MEP was double train: 1st train formed by 5 stimuli with 50 ms duration (ISI
2ms), 2nd train (single pulse 50 ms) ITI
(inter-train interval) 40 ms.
LIMIT: The assessment was possible for the right Orbicularis oris muscle and slightly for
the right Orbicularis oculi muscle.
No responses were obtained from the left muscles (we didn´t increase the
stimulus intensity to look for the better Threshold-level ) and we consider the
absence of other muscle MEP ipsilaterally (e.g. mentalis) as a serious limit of
interpretation.
Right Orbicularis oris
Corticogeniculate MEP decrement
Mapping with 0,3 mA baseline
Mapping with 0,86 mA (after the decrement was seen in CoMEP)
Conclusions:
Ø All
modalities with exception of CoMEP
showed similar findings at the end as at the beginning of the surgery. R1
(Trigeminofacial reflex) was not possible to elicit during this surgery.
Ø Mapping
was useful to drive the surgery moments before debulking and after the surgical
removal of the tumor. We expect partial
facial nerve dysfunction (temporary deficit) in the right side.
Ø 24h
after surgery, the patient showed 60% function of facial nerve preserved, Grade
III (of VI) on House-Brackmann. Other VIII, IX and XII monitored cranial nerves
didn´t show deficit 24 h after the surgery.
Ø CoMEP
as a measure of corticogeniculate motor tracts with different and variable
assessment protocols should be considered as mandatory when trigeminofacial
reflex (R1) cannot be monitored and the interpretation of the amplitude loss
should be verified with anesthesist, neurosurgeons and with T-L technique
(Calancie B, 2017).
Reference:
