Cavernoma Resection Using Intra-operative MRI at The Wellington Hospital Neurosurgical Unit

August 14, 2022

In the summer of 2022 The Wellington Hospital became the first independent sector healthcare provider to open an intraoperative MR imaging facility. The system allows transfer of a patient during surgery into an MR coil where high quality images can be obtained either to confirm completion of a surgical objective or to help direct the subsequent course of the procedure.

The platform chosen is integrated with the BrainLab Digital OR Automated Registration allowing near seamless transition back to the operating position and instant re-registration of the image guidance system based on the updated MR images ensuring optimal accuracy. Below we provide a case illustration showing how this can be applied to neurovascular pathologies.

The patient presented with seizures triggered by a small cavernoma located close to the speech area of the brain in the left frontal lobe. After considering their options they elected to have the cavernoma removed. This was planned through a small incision and a bony door (craniotomy) measuring 2 x 3 cm was raised over the area where the cavernoma was located. A navigation system was used to plot where the cavernoma could be found. This allows the surgeon to point an instrument at the patient and see it virtually represented on an MRI scan carried out pre-operatively. It is reminiscent of looking at a satellite navigation screen and seeing your car virtually represented on the landscape.

Confirm Location in Real Time

One of the weaknesses of such a system is that structures may alter position over the course of surgery. A key step in ensuring no injury comes to the brain tissue is to ensure it remains relaxed by administering medication that reduced the amount of water in the tissue as well as by allowing the cerebrospinal fluid to escape. This results in small movements in the tissue which mean your map can become inaccurate. This is a particular issue when relying on minimally invasive approaches to intracranial lesions when a few millimeters can make an important difference

Intraoperative coronal MRI showing a cavernoma at margin of a craniotomy
A coronal view showing that the target lesion has moved to the periphery of the small cranial opening after drainage of only a small amount of cerebrospinal fluid

The image to the right shows the position of the cavernoma relative to the position of the minicraniotomy after just a small amount of shift has taken place. The cavernoma is no longer located at the centre of the surgical exposure but has shifted with the hemisphere to the inferior edge of the small craniotomy. It can be located with intraoperative ultrasound but carrying out an intraoperative MRI before ANY of the brain tissue is disturbed allows the precise resection of the lesion with the very minimum of disturbance of any functional tissue nearby.

Updating The Satellite Navigation Map

The Welington Hospital's iMRI system here is integrated with the operating theatres "satellite navigation system"- the latest BrainLab image guidance system- which allows the information gleaned from the intraoperative scan to once the patient moves back out of the scanner coil and into position on the operating table.

This is akin to updating ones cars'Sat Nav' map library midway through a journey to take account of changes in the terrain e.g. a new road. The surgeon may then resume confident that the guidance software is as accurate as it possibly can be.

Confirm Removal before Closing

Finally the iMR confirmed that no discernible cavernoma tissue remained an observation confirmed before the patient awoke by an expert Neuroradiologist.

This technology allows microneurosurgery to be as accurate and therefore as safe and effective as it possibly can be especially when combined with advanced neuroimaging techniques to plan operations in advance and intraoperative neurophysiological monitoring. These are the techniques now in routine use at the most advanced neurosurgical centres in the world.

(Images used with patient's consent)

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