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Week: 558.7 Guest: Dr. Gary Hack, DDS, Prof. of Dentistry, Univ of MD. Dental School Topic: A newly discovered neck/brain connective tissue and new jaw muscle Producer/Host: Steve Girard


NEMA: Thanks for joining us again. Dr. Gary Hack, a dentist and professor at the University of Maryland Dental School, has a hobby...one which recently led to the discovery of two new physical structures in the head and neck...and which may help us more fully understand the way things work, and the role these structures may play in some of our most nagging and painful conditions: TMD's, or jaw pain...and headaches....

HACK: Actually, I've always had an interest in temporomandibular disorders. These are disorders of the jaw joint. And one of the main components of that disorder is that the muscles that move the jaw, the muscles of mastication, can become dysfunctional. And I had joined with my colleagues in beginning a series of cadaver dissections, to look at, on a very close level, the muscles of mastication...basically so that we would have a better understanding of this entity called temporomandibular disorders. And as a result of that study of the muscles of mastication, we basically stumbled upon two anatomical features in the human head and neck that have never been described before in the medical literature.

NEMA: It's an amazing thing to find something new after all this time. For you, it must feel great to make this discovery...

HACK: It was unbelievable to us. With this first discovery, this connection between the deep neck musculature and the covering of the brain and spinal cord, we said, "this is an area that surgeons operate on all the time, anatomists have been dissecting human bodies for at least 500 years....this must be in the literature somewhere". We began to do an exhaustive literature search, both in the library, through the computer, and there was absolutely no evidence of a physical connection described between the deep neck muscles and the covering of the brain and spinal cord. And now that we have announced this discovery, scientists and neurosurgeons from all over the world are writing to us, telling us that, yes...now that they know it's there, they're looking for it, and they're seeing it. People assume in anatomy that everything is known, that everything is described in a textbook, and I think they begin to develop a mind set that there's nothing new to learn. But if you begin to dissect and keep an open mind, and say to yourself, "maybe there are new structures, maybe there are new relationships that are not described in the anatomy books". In that way, you begin to see things and appreciate things in a very different way than the anatomy books present.

NEMA: We do stories all the time on new molecular level discoveries, but most of us think the skeletal - muscular system is a known quantity...that there's nothing more to find....

HACK: The ironic thing is that many anatomy departments within medical and dental schools are closing, because the assumption is everything is known, everything is in the textbook. And they're beginning to move toward the molecular, that's where all the scientific movement is moving... towards this sub-microscopic level...and it's assumed that everything at a growth level, the large level is known. I'm hoping that through our discoveries, people will realize that there's still a great deal to learn at this larger, structural level.

NEMA: What has been the feedback from peers and colleagues on the discovery of the muscular dural connection?

HACK: Everything that we have heard, everything that people have said to us about the muscle dural connection has been positive. Neuroscientists, neurologists are beginning to speculate that, yes, this may play a role in some headache conditions. Anatomists are beginning to confirm, in their own laboratories, yes, this structure does exist, even though it has never been described before. Brain surgeons are beginning to write to us and tell us, yes, when they operate in this area, they are definitely seeing this structure each and every time they operate...now that they know where to look. And now the exciting thing is that we're beginning to get some reports that people who have had this structure cut, for whatever reason, are now experiencing less headache pain than they had before the procedure was done. So, some very exciting things are beginning to happen, in particular, one group is very excited about this is the chiropractic group...because they have claimed for years that they can relieve headache by manipulating neck muscles and neck structures, and this may be an anatomic basis for why their therapy works.

NEMA: Now we have another structure that may be responsible for headaches, but what do you speculate the purpose of this structure is...what does it do?

HACK: Now, one of the things that is interesting, and we're beginning to think about this, obviously, in terms of great detail, is this structure...this bridge that goes from the muscle to the dura, is in an area right at the base of the skull. And just deep to this dura is fluid...the brain fluid that surround the brain. And we know that when the head is tipped backwards, this dura has a tendency to buckle inwards, or to kink inwardly...potentially compromising this fluid flow. What we speculate is that the function of this connection may be that in backward head movement, contraction of the neck muscles could pull on the dura, through this connective tissue bridge that we've described, and prevent this kinking or folding of the dura that may compromise what is called cerebro-spinal fluid flow. So, obviously this is speculation on our part, we can't say for sure what the function of this connection is, but this is one possibility we're considering.

NEMA: What's next? And being as how you are a dentist, and an instructor...and this is not really your field...but more of a hobby. You kind of have to let your discovery go...and follow along from the sidelines....

HACK: This is a very good point that you make, because indeed, I am a general dentist...and this is clearly an area that is beyond my expertise. So, in a sense, I have to let it go, and I have to let the brain surgeons and the anatomists and the neurologists begin to look at it. But I also can continue with it on other levels. We can continue the dissections to see if there are other, similar types of connections throughout the cervical spine. We can begin to look at the histology, we can begin to look at animal models, and another very exciting thing that I'm becoming very intimately involved in is... The National Institutes of Health developed a project called The Visible Human project...where they took a human cadaver, and actually sliced it in five thousand sections. Each one of those sections was photographed and fed into a computer. So now, what you basically have is a digital man. You can go into the computer and do three dimensional reconstruction's of any part of the body or any area of the body. Because you have all this information from an actual human cadaver...and we are now confirming the existence of this connective tissue bridge in the Visible Human project. Working with a number of engineering and software companies, we're going to hope to develop models, that is, functional models, through the computer to begin to analyze what the potential function of this structure may be...and what happens in pathology. So, some very exciting things are happening that I'm hoping to stay very closely involved with...in this project.

NEMA: Now let's switch gears a bit....to another anatomical rabbit you pulled out several months ago. The discovery of a new muscle in the face. Tell me about that....and who worked on it with you.?

HACK: Dr. Gwendolyn Dunn and I are co-discoverers of this sphenomandibularis muscle. What we have found is a muscle which is not described in anatomy textbooks. We know that there are four known muscles - chewing muscles, muscles that move the jaw in chewing, and we believe that this may be a fifth muscle of mastication. That is, those muscles that move the jaw. If you look in any anatomy textbooks, when they dissect out the main chewing muscle on the side of the head, which is called the temporalis, they always approach the dissection from the side...from the side of the head. And what we had done, Dr. Gwendolyn Dunn and I, is something very unique: we approach the dissection from a totally different perspective. Instead of going from the side of the head, we went from the front. And when we did that, it allowed us to see a structure that was deep, or inside of the temporalis, that is not described in the anatomy books. The bible of the anatomy books is Grey's Anatomy, and Grey's makes absolutely no discussion or description of this muscle. We are calling this new muscle the sphenomandibularis, because it runs from the sphenoid bone...at the base of the skull, to the mandible, which is the lower jaw. And actually this muscle attaches to a bony structure just behind the eye socket. Interestingly, we know that in some jaw joint problems, when the muscles have certain spastic problems, people can experience pain behind the eye. And what we have now found is what we think is a chewing muscle that actually originates from immediately behind the eye. So again our speculation is that this new finding, this new muscle, the sphenomandibularis, may indeed have something to do with retro-orbital pain, that is pain behind the eye in people who suffer from temporomandibular disorders... particularly those that have dysfunction of the muscles of chewing.

NEMA: What other problems do you believe it may cause?

HACK: We are beginning to speculate beyond TMD, or temporomandibular, or jaw joint disorders. That is our area, in dentistry, dentists certainly treat these conditions. Now there are other types of headaches, where people experience pain behind the eye, cluster headache, for example, experience extreme, severe pain behind the eye. And we're beginning to look at what the potential is...that this structure, that we never knew existed before, may indeed play a role in some of those types of headaches. So the fact that you find something new, something new in the human head and neck, something of significant size...this finding opens many doors of possibility, in terms of what it means, what it means in function, and what it means in disease states. How do you uncover what the cause of a particular problem is unless you know what structures are there? And by having this structure there, it's like a missing piece of the puzzle...there's no way that you can fully understand a condition unless you understand the anatomy. The anatomy is the basic building block. And what we're finding from our discoveries is that all of the building blocks are not known. And it becomes impossible to truly understand these conditions if the basic anatomy is not fully understood.

NEMA: Maybe a great side effect of your finds will be new interest in double checking what we know about ourselves...

HACK: I hope so, because one of the things that happens is that when you do dissect, you destroy the structures as you move along. You destroy relationships...you push things out of the way. And once you've done the dissections from a particular point of view, you really can't go back to another perspective, because you destroy those structures. The head and neck is such a complex entity, there're so many structures in there, that dissecting becomes such a tedious and challenging way to truly understand the anatomy, and I think that's why some of these things have been missed, even after hundreds of years of dissecting and of surgery.

NEMA: Thanks to Dr. Gary Hack of the University of Maryland Dental School. To find the transcript for this program, and others from the past year...you can visit our web site. Here's the address:


Or you can call 800-332-6362 for more information on The National Emergency Medicine Association. I'm Steve Girard for The Heart of the Matter!


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