brought to you by the nerve stimulation experts at Neurosign

June 19, 2024

Revision acoustic schwannoma



This lady had a suspected meningioma excised a few years ago, but it was diagnosed as an acoustic schwannoma once the tumour was examined by histology. As it was thought to be a meningioma, the internal auditory canal was not opened and tumour was left within the canal; it is assumed that it has regrown from the canal.
The tumour is about 3cm and is severely affecting the trigeminal nerve. The patient has numbness in the face and pain, but can still chew.
The goal is to obtain a complete clearance.

As this is a revision, it cannot be assumed that the tumour capsule will have pushed the cranial nerves out of the way; the nerves may now be passing through the tumour. The surgeon will need to be especially careful and pay attention to the monitoring so that the affected nerves can be found and identified.


I am using my standard ‘acoustic’ protocol; 4 branches of VII, V, IX, X and XI. I am using the Neurosign V4 to monitor the facial nerve, as the stimulator on the V4 can go as low as 0.01mA, as opposed to the 0.05mA of the Neurosign 800. I am using the Neurosign 800 for the trigeminal, glossopharyngeal, vagus and accessory nerves (V, IX, X and XI).

After the patient was positioned on the operating table, the Neurosigns were connected and electrodes checked. All channels show flat lines; impedance check on the V4 showed green (for low impedance)

1030 patient draped, knife to skin. As the patient has had a previous craniotomy, less drilling will be needed to gain access.

1150 microscope in

1230 surgeon exploring down the sides of the tumour capsule and then debulking centre of tumour. Probe used to check for nerve fibres. Possibly identified XII, but no needles in the tongue.

1240 X identified and stimulated

1315 ENT surgeon has started to take canal wall down. Facial nerve responses as wall is drilled.

1415 facial nerve stimulated in IAC at 0.05mA and tumour cleared

1500 neurosurgeon stimulated facial at porus @0.05mA

1515 trigeminal nerve stimulated @0.2mA and good response obtained – patient has facial numbness prior to surgery

1645 surgeon has removed as much of the tumour as is practical; trigeminal has been decompressed (patient had facial numbness and pain); the motor element of the trigeminal is functioning; the facial has not been identified at the brainstem but the tumour has been cleared from the IAC. Patient will be sent for radiosurgery for fdurther treatment.