brought to you by the nerve stimulation experts at Neurosign

July 13, 2024

Large acoustic schwannoma



This middle aged man has a 3.5cm acoustic schwannoma and severe ataxia, deaf on the affected side. He is otherwise healthy, though a little overweight.

From a monitoring point of view, he is straightforward; 4 channels for facial nerve, trigeminal, glossopharyngeal, vagus and accessory. On the scan, the tumour appears solid with a cystic component, and given his age and state of health, I would expect a total clearance to be attempted. Any residual tumour will be treated with radiosurgery.

The patient has no neurological issues before surgery (apart from the ataxia).

The craniotomy has been completed and the dura opened, cerebellum retracted. Surface of tumour stimulated at 1mA, no response.

Tumour capsule explored and IX, X and XI visible. Stimulated these at 0.25mA and facial nerve response obtained. Further exploration and facial nerve stimulated at 0.05mA in this area.

Tumour being debulked.

Trigeminal identified at 0.4mA. Gives an odd response, difficult to see take off point reliably, but appears delayed at more than the usual 3.2ms. Causes the face to respond as well every time, so more confusing than usual. This may improve as Vth nerve is separated from tumour.

With much of the tumour debulked, the lower cranial nerves are now easily visible, with a strap of tumour running parallel to the lower cranial nerves. AICA is running in the same plane but is not attached to tumour. The facial is also running down the back of the tumour, parallel to the lower cranial nerves, and enters the brainstem next to them, so that stimulating here gets the facial or lower cranial nerves with little movement of the probe. All in all, very unusual anatomy!

However, nerves are stimulating well at 0.05mA. Surgeon is going to remove remainder of tumour not involved with the nerves and then leave some capsule on the facial, to be treated by radiosurgery later.