Taking the guesswork out of brain surgery

Brain_tumor_resection

Trick to removing a tumor from the brain is knowing where to cut. You would assume that your incredibly smart neurosurgeon would be able to tell the difference between brain and tumor. Cut out the tumor. Leave in the brain. Sounds simple, right?

It turns out to be not that simple.

Lets talk about where cancer comes from in the first place. You could think of your body like a city where each citizen has a specific role — accountant, janitor, teacher, physician, trader, farmer etc. To make the city function, each citizen has to contribute their bit. And for each citizen to be productive, they need resources to be distributed equitably (though not necessarily equally) among them. Cancer happens when some citizens decide that they are too good for the work they do. And they deserve much more than the share of resources they are currently getting. The 1% economics works no better for the body than it does for societies.

Cancer is our own cells gone rogue. They look and act like normal healthy cells in some ways. No surprise then that a surgeon might have some trouble telling them apart from healthy tissue. These tumor cells are good at blending in, but not that good. For instance, it’s selfish nature is a giveaway. Body’s resources (nutrients, oxygen) are distributed through blood. When a cancer tries to hog as much blood as possible, it does so by making new blood vessels, through a process known as angiogenesis. These new blood vessels tend to be leaky, which forms the basis of contrast enhanced images where the tumor lights up.

Contrast enhanced MRI image. Source: http://openi.nlm.nih.gov

Contrast enhanced MRI image. Source: http://openi.nlm.nih.gov

While you can see the tumor, the trickiness lies at the edges, which look all murky.

Brain tumor. Source: (Okuda, J Clin Neurosci)

Brain tumor. Source: (Okuda, J Clin Neurosci)

Neurosurgeons face a dilemma. Get too aggressive, take out too much, and risk cutting out parts of the brain along with the tumor that the patient needs for important things like walking and talking. Not be aggressive enough, leave too much tumor behind, and the cancer comes back with vengeance.

Different technologies are under development to help surgeons define the brain-tumor boundary better. One of these methods bounce a laser light on the brain (or tumor) surface. Light comes back in two forms — reflection and fluorescence. Reflection is quite simply the light you would see in a mirror, some percentage of the light bounces back and you see a likeness of yourself. Fluorescence is an internal property of objects where they absorb the light and then emit it, but the wavelength coming out is different than what went in. This how the energy efficient fluorescent light bulbs work. Different objects behave differently, reflecting different percentage of light or fluorescing different wavelengths, forming their own signature. Brain and tumor, because of their inherent differences would have their own signatures, a fact that is being exploited by researchers to help surgeons guide where to make the cut.

Another technology that helps distinguish between tumor and brain tissue uses mass spectrometry. You might remember this technology from any number of TV crime shows. Splatter of grime on a victim’s shirt showed traces of compound X, commonly found in car paint, so the car mechanic must have done it. Recently published paper in PNAS uses mass spectrometry with a twist to tell the difference between brain and tumor tissue. Normally to analyze samples in mass spectrometer, they have to be specially treated, suspending them in vacuum. Needless to say, that it would make it tough to use while operating on the brain. This new type of mass spectrometry, termed desorption electrospray ionization (DESI), lets a user perform mass spectrometry analysis on sample outside, without a need for special preparation in vacuum. Here’s an explanatory video of this technology from the company that has commercialized DESI.

Just like researchers who used the inherent difference in florescence of brain and tumor, these researchers use the differences in the outer membranes of brain and tumor cells that are detected by DESI-MS to guide neurosurgeons.

Neither of these technologies is currently in use in operating rooms, but hopefully in the near future these tools will take some guesswork out of brain surgery.

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  • Legalese

    The purpose of this blog is to share interesting bits from around the web and beyond. All opinions expressed on this site are my own, unless credited to someone else. The images and artwork have also been created by me, unless credited to the sources. Oh! And please don't hold me liable for your actions resulting from any information on this site. As with everything else on the internet, read with the requisite amount of skepticism.
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