Quote Originally Posted by NowhereMan View Post
Hi Dr. Wise,

I am a c6/7 complete inury from a motor vehicle accident, and no bone or object penetrated my cord. Yet, i saw an MRI of my spinal cord and above and below the injury site was the cord but at the injury site was a gap, full of celebralspinal fluid. So my spinal cord is severed from a contusion injury, otherwise there would be no gap with fluid in it. So my question is, why wouldn't you consider that a severed spinal cord? and how would repairing my injury be any different than the one you are reffering to above in Clementine's case? Does that make sense? thank you Dr. Wise

The spinal cord is covered by three membranes. The first is on the surface of the spinal cord, called pia mater. Then there is the arachnoid, a thin vascular layer. Cerebrospinal fluid is usually between the pia and the arachnoid. Finally, there is a thick membrane called dura mater (literally meaning hard or tough mother).

It takes a great deal of force or a sharp knife to cut through all three membrane to severe the spinal cord so that there are two separated ends of the cord. That is why a "severed" spinal cord is very rare. Even when there is a jumped facet where the front end of one vertebral body is locked behind the back end of another vertebral body, essentially reducing the spinal canal to a few mm at most, the spinal cord is seldom severed.

When the spinal cord is contused (rapidly indented) or crushed (compressed to a small fraction of its normal diameter), the tissue is damaged and cells at the injury site die. The dead tissue is cleared out by macrophages. In most people and animals after contusion injuries, the injury site becomes filled with loose matrix of cells that include macrophages, astrocytes, and stem cells. In fact, axons can often be seen growing into the injury area.

In 15-20% of people, the space may be filled with cerebrospinal fluid. Note that the space may look empty but a thin rim of tissue usually remains just below the pial surface. That rim of spinal cord may be only 1-2 mm think and contains myelinated axons. Most MRI's have a resolution of about 1 mm and therefore can barely show that rim. In some people, syringomyelic cysts (enlargements of the central canal) develop above and below the injury site and may communicate with the injury site to fill it with cerebrospinal fluid.

If you transect (cut through) the spinal cord, three things happen. First, you are cutting through blood vessels, particularly the anterior spinal artery which supplies blood to the anterior and middle of the spinal cord. Note that the blood supply of dorsal and outer part of the spinal cord comes from posterior arteries that enter alongside the posterior sensory roots. The loss of blood flow causes the two stumps to die back.

Second, through most of its length, the spinal cord is under some tension. So, when you transect the spinal cord, the two ends tend to spring apart. In rats, there is only one place in the spinal cord that does no spring apart when you transect the cord and this is at T10. Certainly, with movement, the two ends of the cord will spring apart. Axons will not grow across empty spaces and therefore a gap between the two ends of the cord represent a significant obstacle to regeneration.

Third, cells from outside the spinal cord, i.e. fibroblasts, invade into the area between the two stumps. Fibroblasts are skin cells that form scar tissue. On the spinal cord side, astrocytes will grow and line the stump. This is a true "glial scar" that has collagenous scar and glial cells facing each other. However, such a scar seldom forms in the contused spinal cord unless there is a penetrating wound.

When there has been a penetrating wound of the spinal cord, the injury site often feels hard and lumpy, due to the scar. The dura may have been torn. Most surgeons will just clean up the area and may try to repair the dura. Animal studies have shown that that there is a difference in the recovery of the animal after the spinal cord is cut, depending on whether or not the dura is repaired and closed. Recovery tends to be better if the dura is repaired.

I am not saying that spinal cord transections cannot occur. They do occur, particularly in cases where a bullet has penetrated into the spinal canal, in thoracic spinal cords (which usually involve high speed impacts that are sufficient to tear all the ligaments holding the vertebral bodies and that cause the vertebral body to "scissor" the spinal cord, and in knife or sword cuts of the spinal cord.

But, even in cases where a sharp knife is used to cut the spinal cord, part of the spinal cord may remain. For example, I have seen two cases of knife-inflicted cuts of the spinal cord. Both times, the knife cut three-quarters or two-thirds of the cord, severing the vertebral artery on one side and possibly the anterior artery in the middle, leaving a third to a quarter of the spinal cord on one side. This often results in a Brown-Secquard syndrome and people can recovery walking after such an injury.

Coming back to your situation where the MRI is showing an empty space at the injury site, filled with cerebrospinal fluid and surrounded by a thin rim of spinal cord. Presumably axons can grow in the thin rim of cord. Cells injected into the surround cord may migrate into the rim and fill it out. We don't know whether this is the case and therefore, at least in our first clinical trial involving transplants, decided to exclude those patients who have a large cyst in the middle of the cord that occupies more than half of the diameter of the cord.

In future trials, we would like to assess the effects of cell transplant in these patients, to see if cells injected into the surrounding cord will move into the "empty space" in the injury site and fill it. We know that this occurs in animals and hope that this would also occur in humans.