The integrity of our circulatory system is maintained by critically balancing the tendency to leak, with that to clot. In an intracerebral hemorrhage, blood leaks into the brain, and then forms a massive clot. Treatment with drugs is a precarious path because those that break down clots can also make any residual leak worse. A minimally invasive way to get to the problem mechanically, rather than chemically is now being developed by a group of researchers at Vanderbilt University. With a steerable robotic device that is introduced to the brain much like an arthroscopic probe, the researchers can navigate around critical structures to get to the clot, and then suction it out.

The issues involved in getting inside the brain to treat vascular pathology, or even a tumor, are much the same as those for accessing the brain for electrical stimulation. We have discussed some solutions previously for reaching deep brain structures either transnasally, or perhaps through the ventricular system, but surgeons have been slow to adopt such techniques for things other than pituitary surgery. The Vanderbilt team, which had previously developed a steerable transnasal probe for removing pituitary tumors themselves, realized that their device could be repurposed for clot removal.

The researchers call their instrument an active cannula, and it is basically a series of nested tubes with different curvatures. By rotating, extending and retracting the tubes, the tip of the probe can be controlled as it is introduced to the brain under the guidance of CT. To look at the device, it does not appear all too complex, and if I may be forgiven, perhaps even a little bulky. With a diameter of 50 thousandths of an, inch there is likely room for further miniaturization, and addition of other tools. The team would like to add ultrasound imaging, perhaps using a probe-mounted sound source much like that commonly used to generate a transesophageal echocardiogram of the heart.

There are many ways to steer catheters, but the best method depends on the application at hand. A modern catheter may have several concentric bores and side channels of different sizes depending on the tooling to be used inside. Fiber optic illuminators, cameras, drug delivery, suction, heating, radiofrequency ablation and various steering apparatus all have their own special mechanical requirements. For now, most of these tools are integral to the catheter, but increasingly, we are seeing end-effector tools that are deposited inside the tissue and given a chance to work independently. Stents, balloons, magnetically guided drug delivery vessels, and radiation emitters or absorbers comprise the modern medical arsenal which critically depends on precise delivery.

The researchers are also developing computer models of how brain tissue deforms when it is pushed upon. Not only should it be expected that white matter would behave differently from grey matter, but we might expect that white matter has isotropic properties that would depend on the directions of the axons within it. Having a white-matter connectome for the individual prior to surgery would permit the least damaging access trajectories to be considered beforehand. Adding vibrating elements, slight heating, or enzymatic release capability to the tip might even allow the probe to safely displace whole axon fields and pass through them like a caper through spaghetti.

The device has already been tested on brain phantoms that the researchers constructed to mimic the gross material properties of the brain, and hopefully it will be made available to surgeons for the treatment of this very widespread condition.

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