A Primer on Brain Mapping
On Tues ., Feb . 7 , the GLMS Foundation Senior Physicians Speaker Series welcomed Dr . Jeffrey E . Florman to speak on new trends in brain surgery and brain mapping . Interim Chair , Dr . Sam Yared , shared that Dr . Florman ’ s father is Dr . Larry Florman , well-known and respected plastic surgeon in town , and he soon followed in his father ’ s footsteps and attended medical school at the University of Louisville , going on to complete his internship and residency in neurological surgery at the University of Vermont Medical Center . He is currently practicing in Maine and has extensive experience in treating the nervous system , neoplasms , cranial neurosurgery and neurocortical care disorders .
Brain mapping is essentially localizing specific brain functions to specific areas in a specific patient . As brain mapping has evolved over the years , we now have a good understanding of just where things such as motor , sensory , language , vision , memory and high cortical function live as a general rule , but all patients are different .
For a lot of patients , Dr . Florman said they use “ practical mapping .” Using historical anatomic maps , he can easily look at a scan and tell that a lesion is or is not near a language area or primary motor cortex . This can make them less worried about a lesion if it is far from eloquent brain areas or if it is superficial or has a lot of surrounding edema . There are challenges , though , in that many brain tumors are infiltrative with microscopic “ fingers ” that go through the brain or there are lesions that are very close to a language or motor area , making them more difficult to approach . Also , deep lesions , those on the dominant side ( on a right handed person , the left side is more language and memory areas ), or congenital or longstanding lesions can be mapped . Additional challenges present themselves when you look at the surface of the brain , and it can be difficult to determine where the tumor is with your eye ; the anatomy can be very distorted , and boundaries can be difficult to define .
To map the brain for a patient , imaging is essential , often using CT / MRI as well as functional MRI and magnetoencephalography ( MEG ). With only a handful of MEG machines around the country , this technology is rarely used . It ’ s a superconductor-based technology that looks at electrical activity while people are doing tasks . We can also use non-invasive , non-imaging-based things like neurocognitive testing .
In looking at a few specific examples , Dr . Florman asks , “ Is this resectable ? Is there functioning brain in the tumor ? Or is the function ‘ reorganized ’ or pushed to the side ?” The bottom line is that sometimes , determining “ resectability ” is often impossible preoperatively . “ The best maps are drawn with the head open ,” he said .
Intraoperative mapping has been around for a long time , but has been used increasingly in the last decade as anesthesia has evolved . The functions we can map include motor and language function , while sensory and vision are a bit more difficult to do .
by KATHRYN VANCE
When using Somatosensory Evoked Potentials ( SSEP ), we take an electrical grid , straddling the central sulcus where there is motor and sensory function , and look for a phase reversal . Put simply , with someone asleep in the operating room , we can determine where the motor and sensory parts of the brain are , just by the way peripheral stimulation electrically causes a signal in the cortex . Using Motor Evoked Responses , they can stimulate from the top down , electrically stimulating the motor cortex then measuring the response in the muscles peripherally . Using cortical electric stimulation , we can use grids or strips to perform bipolar stimulation , indicating where we are “ inside .” In the example Dr . Florman showed , we can literally number parts of the brain to indicate whether a particular part “ didn ’ t do anything ” or “ caused the arm to move ” or a variety of other language or motor functions . While motor and sensory cortexes are pretty consistent , language is less predictable . Even with MRI mapping , intraoperative mapping can be much more accurate .
“ At the end of the day , sometimes if we ’ re really trying to do an aggressive resection , we ’ re better off just waking someone up in the operating room and identifying the things we ’ re trying to protect . It has proven an incredible adjunct to identify these things so that we can optimize the extent of our resection ,” he said . But , we must choose patients that this makes sense for . Selection criteria for an awake craniotomy include lesions proximate to language / motor / sensory cortex , the proper psychological profile and an uncomplicated airway .
These procedures can of course come with complications . Intolerance can occur , with pain control issues , agitation and confusion . There is also a chance of seizures or airway issues such as obstruction , desaturation or hypercapnia .
He said they ’ ve developed a practical approach for awake craniotomy , shared with several other institutions around the world . They use a very simple anesthesia protocol : some narcotic , Propofol to “ do the stuff that hurts ” and some generous local anesthesia . They try to stay away from things like anxiolytics because it can cause adverse reactions such as fogginess or uncooperative behavior . They also use anticonvulsants , as seizures are very common , and neuronavigation-specific , high-tech computers help to point to the tumor .
After looking at a few cases in further depth , Dr . Florman closed his presentation with a quote from a friend , French neurosurgeon Dr . Hughes Duffau , who said , “ See the brain , not the tumor .” Dr . Florman expanded to say , “ When we get in there , we ’ re not looking to say , ‘ I think I see the edge of the tumor ,’ we just say , ‘ We know the tumor is in this piece of brain , we know there ’ s function here . We ’ re going to go all the way over to the edge of the function and draw a line and then we ’ ve got a maximum extent of resection . So we have this idea of seeing the brain , not the tumor . And it works .’”
Kathryn Vance is the Communication Specialist at the Greater Louisville Medical Society .
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