The goal of all brain tumor surgery is really to get what we call a maximal safe surgical resection. Which means that we want to remove all of the tumor but we don't want to have any negative effects on the surrounding normal brain tissue. Prior to any brain tumor operation in eloquent cortex, the patient is admitted to the program for translational brain mapping.
All of the information that we get from the functional MRI scan is actually used to improve the outcome of the patient at the time of surgery. This particular patient underwent fMRI prior to surgery and this evaluation revealed that the tumor resided within the superior frontal gyrus, immediately anterior to the motor cortex. It revealed that there was no direct language representation over the tumor.
It revealed that the supplementary motor area language representation was confined to the opposite hemisphere. And finally, it revealed in the DTI analysis that the frontal aslant tract was located anterior to the anterior margin of the tumor. We always start with a patient having a dominant frontal tumor resection with the patient in a lateral decubitus position, but then we roll the patient back so that we don't have to place an axillary roll.
We put pillows and other foam devices around the patient so that when they do wake up and spend an hour or perhaps two hours during the mapping procedure, that the patient will be comfortable during the procedure. We then have to place the Mayfield head holder and we position the head holder over the scalp. We then inject local anesthetic where the three pins will be placed.
We fixate the Mayfield device to the table and to the skull. We then register the patient's head to the pre-operative MRI using a cranial navigation system. At the University of Rochester we use Brainlab for inter-operative navigation and the system has worked extremely well for us on a number of levels.
A very important step of the operation is to perform the local anesthetic block. We use probably 30-40cc of local anesthesia in each case. And the first stage of the blockade is to inject the incision along its entire extent all the way to the skull.
And then we perform regional blocks which block, in this case, the supraorbital nerve, the auriculotemporal nerve, the greater occipital nerve, and then we perform deep muscle blocks which block the temporalis muscle and the area just above the ear. Contemporaneous with our efforts to comfortably position the patient the neurophysiology team is preparing for the inter-operative monitoring that they're going to be performing. The cognitive science team is setting up their equipment.
When the patient wakes up in the operating room, there's a small monitor that's positioned in front of them and attached to that monitor is a microphone and a speaker and a video camera. And this allows us to duplicate in the operating room everything that we're doing with functional MRI when we study the patient before surgery. The advantage of the overhead table is that the anesthesiologist and the nurse practitioner, as well as the cognitive scientist and the neurophysiology team, all have access to the entire patient during the operation.
We prepared a craniotomy that was sufficiently large to allow us to map the majority of the motor cortex. That would allow us to map any language function within the middle frontal gyrus. And the craniotomy would also be large enough to allow us to obtain anterior margin of tumor in the anterior portion of the superior frontal gyrus.
This differentiates our approach in this particular case from more minimalist approaches in which negative responses are acquired from the region of direct tumor resection. Once the scalp is completely open, the first thing we did in this case was to mark out the location of the tumor, to mark the midline, and then to begin to decide where we would place our burr holes and where we would make the saw cut. Once the dura was completely opened and the bridging veins had been protected and separated from the medial aspect of the dura, the next goal was to attach the electrocortigraphy device to the skull clamp so that we would be able to test after discharge thresholds and to perform electrocortigraphy during the entirety of the procedure.
Prior to beginning the brain mapping portion of the operation, we register the bipolar stimulator in the same space as the pre-operative MRI using the cranial navigation system, in this case, Brainlab. This allows us to record a 3-dimensional coordinate for each location of direct electrical stimulation. After surgery, we can carry out quantitative analyzes that relate pre-operative functional MRI with he consequences of inter-operative stimulation mapping and ultimately with patient outcome.
At the very beginning of the brain mapping procedure we usually begin with motor mapping. Starting in the tongue area with the patient protruding the tongue and then stimulating at a very low milliamperage level, usually 5 to 1.0 milliamps, and looking for tongue retraction or facial movements which would indicate that we were successfully mapping motor function. Ah, look at his hand.
Wrist rotated. Tell me if you feel anything tingle. Right elbow?
Right elbow, perfect. You read the textbook. Tell me if you feel anything now tingling.
Ah, right neck. Up in here? More to the back.
In this area the tumor appears to end right here. This is motor for the finger and hand and wrist and arm. Leg motor is, in all likelihood, right here.
And this is all sensory, we had really good sensory responses in the hand and all the way up to the shoulder and neck. And so now the goal is to take the tumor and continue to map, with his active participation, to map the foot motor activity because this posterior margin of the tumor is a key area we want to remove without causing any weakness in the leg. We elected to begin the tumor resection in the posterior margin of the tumor, immediately anterior to the motor cortex.
And the purpose of this decision was, while the patient was awake and fully cooperative, was to begin the debulking posteriorly to identify the anterior peel bank of the leg motor cortex to denude the peel bank of tumor, and possibly infiltrated white matter, and with the patient performing various tasks with the upper and lower extremity, we were then able to completely resect the tumor at its intersection with the rolandic area. Once this initial resection was completed, we were then free to begin the anterior portion of the tumor resection, and the deproportion of the tumor resection anteriorly. Recognizing that if the patient's ability to cooperate should change, we had already performed the most dangerous portion of the operation successfully.
The reporting of patient movement, the reporting of patient dexterity, with precision, is extremely important. And in this particular case, the nurse practitioner, Susan Smith, who has worked with us in these operations for over 20 years, and who has experience with hundreds of similar operations, her reporting constitutes an extremely important part of the operating team. Check his foot.
Flex your foot up and down. Wiggle your toes, push down on my hand, pull up hard, nice and strong. Thank you, Sue.
You're welcome. In similar cases where the tumor is located more anteriorly in the superior frontal gyrus, we have been able to identify involvement of the frontal aslant tract on DTI pre-operatively and we have successfully been able to map the frontal aslant tract with sub-cortical stimulation mapping. The yellow triangle is above the red diamond.
The green circle is above.the. Keep going We obviously warned the patient and his family that a transient SMA syndrome could occur. We did not make an attempt to map the supplementary motor area because it was completely involved with tumor.
And indeed, post-operatively the patient had a subtle SMA syndrome with some expressive aphasia and some incoordination and very slight loss of motor control in the right upper extremity. But this faded quickly and by the time of discharge at Day 5 the patient's examination was normal. Over the last couple of years as we have evolved our translational brain mapping program, and as we have worked increasingly closely with our cognitive science colleagues, we have developed a nimble ability to tailor the operation and the brain mapping component of the operation to the needs of the patient depending on the location of the tumor.
As a consequence, we have now developed significant experience with mapping of number knowledge and mathematics. 53 plus 18 equals 71.65 plus 16 equals 81. We have also developed significant experience with the mapping of different aspects of language function, including naming, reading, and repetition.
Here is a in, inger. This is a hot mouth. And we have also developed more recently the ability to map music function in the non-dominant hemisphere.
Brain mapping really allows us to be as complete as we can with surgery while maintaining a margin of safety for the brain tissue around the tumor that we're trying to preserve at the end of the case. Every time we do an operation on a patient with a brain tumor or with epilepsy, every time we do an operation we have an opportunity to learn something more about the brain.
