Cath Lab Digest

What is PIN?
PIN stands for percutaneous intraspinal navigation. Just as we’ve been using the arteries as a conduit to navigate the vascular system for a long time, we also believe it may be possible to use the space surrounding the brain and spinal cord — the so-called sub-arachnoid space — to navigate in and around the brain and spinal cord. We've known for a long time that you can access that space by putting a needle in the back. Currently, people visualize the spinal cord via myelograms and also perform lumbar punctures to draw some of the spinal fluid. Another way that people have accessed the subarachnoid space is through the brain. Neurosurgeons put in ventriculostomies, or shunt catheters, to treat hydrocephalus. So, the concept is not new. It's probably a little more developed now, but PIN is essentially the concept of putting catheters in the subarachnoid space to treat that space just like it was the inside of an artery, using tools that we use in interventional radiology, like catheters and guidewires, to navigate that area and also move around the surface of the brain.

How do the catheters and guidewires that you are using compare to the standard interventional equipment?
What I've been doing so far is using off-the-shelf technology — basically the exact same devices that we use for angiographic procedures, but adapted for these procedures. I personally believe that there is a whole new family of technologies which could emerge if PIN develops and people start incorporating it into more routine activities.

For instance, there are structures that we may want to access where we can use a combination of x-rays and direct visualization. We've been working with some different types of endoscopes on catheter-type devices in order to look at the brain or spinal cord from inside the subarachnoid space. These devices also have channels where we can pass guidewires and other things through to be able to perform surgical procedures. However, the types of procedures that endoscopes are now developed for are things like bronchoscopy. There are a few endoscopes that have been developed for looking inside the blood vessels, but none really have the type of flexibility and the field of view that we would like to have for managing the subarachnoid space, so there are some adaptations that could be made in endoscopic technology.

We also have experimented with the use of MR imaging to guide the navigation and to watch as we are passing catheters and devices up alongside the spinal cord and the brain. However, the types of tools that are available for interventional MR procedures are really pretty primitive in terms of resolution, as well as any use of those tools to interact with the MR scanner technology to generate better information about your location with respect to the surrounding structures.

What types of conditions do you believe this procedure could address?
When you put a catheter or device into the lumbar space, the first thing that you encounter is the nerve roots coming off of the spinal cord. Working with cadavers, we've done endoscopic procedures which look at nerve roots and experimented with the manipulation of these nerve roots from a percutaneous approach. The typical way this area is approached surgically, such as with a laminectomy, is where you actually remove bone to open up and visualize the area. We also believe that there are some ways that we can use electrophysiology to test for nerve damage or nerve malfunction, or to possibly treat pain syndromes. Right now, they use neurostimulation of electrodes as a form of treatment, and with PIN, you can get more precise placement against nerve roots or adjacent to nerve roots, since we can look at them directly.

As you move up towards the brain, you reach the area alongside the spinal cord. There's a whole lot of work being done right now with stem cell implantation for spinal cord injury. Also, different places are working with spinal cord hypothermia. Devices that are introduced through the PIN technique should be really ideal for these two types of treatments, because it saves a whole operative procedure along with the attendant risks and discomforts associated with it.

Moving on up towards the head, you can have abnormalities in the subarachnoid space, or the space around the brain, where blood vessels sometimes press on nerves or press against nerve roots and cause pain sensations in the face. These are called Tic Doloreaux, or facial tic. Neurosurgeons will put devices between the blood vessels and the nerve roots to keep the blood vessels from pulsing against the nerves, which is another procedure that might be feasible via the PIN technique. We know for sure that it is possible to pass a catheter up into the ventricular system, because we’ve done that and reported it in the literature.¹ We believe that there may also be some patients who have increased pressure in their brain, hydrocephalus, who could be treated with this type of a surgical approach. Neurosurgeons currently do a procedure that they call a third ventricular fenestration, where they will take a piece of skull off and go down between the right and left hemispheres of the brain to the corpus collossum, and go into the ventricular system that way, in order to make a hole in the bottom of the third ventricle. We’ve shown that PIN can do essentially the same thing, without doing any kind of brain surgery.