Visualization of the Muscle-Dural Bridge
in the Visible Human Female Data Set

Thanks to Gary D. Hack for the use of this article!

BY Gary D. Hack (1), Peter Ratiu (2), John P. Kerr (2), Gwendolyn F. Dunn (3), Mi Young Toh (4)

1.   University of Maryland School of Dentistry
2.   Engineering Animation, Inc.
3.   University of Maryland School of Medicine
4.   National Library of Medicine


We have described (1) a previously unreported anatomical connection between a deep occipital-cervical muscle, the rectus capitis posterior minor and the dura mater, observed in 15 cadaveric specimens, and clinical MRI scans (figure 1.

A connective tissue bridge between the rectus capitis posterior minor muscle and the dorsal aspect of the spinal dura mater at the atlanto-occipital junction was observed in cadaver dissections of fresh (figure 2.) and fixed (figure 3.) specimens. The fibers of the muscle-dural bridge were oriented primarily perpendicular to the dura. This arrangement of fibers appears to resist movement of the dura toward the spinal cord.

Using EAI's visualization technology it has been possible to identify this structure in the Visible Human Female data set. We have reformatted the data set by reslicing it first in the coronal and the sagittal planes. We have also reformatted the data set in five more, non-conventional planes, between the sagittal and coronal planes, at 15 degrees increments (figure 4.). These planes afford a better visualization of the muscle-dural bridge than the conventional, sagittal and coronal planes. As a general observation, most structures are best identified when the sectional plane is either perpendicular or parallel to the long axis of the respective structure. Therefore, we expected to gain a better view of the muscle-dural bridge in planes parallel to the rectus capitis posterior minor muscle. Indeed, in the planes that are offset by an angle of 60 to 75 degrees from the coronal plane not only the RCPM is clearly visible, along with its attachment on the atlas, but also the connective tissue superior to the muscle, which clearly appears to protrude between the occipital bone and the atlas into the spinal canal. In figure 4, we have also noticed muscle fibers that do not follow the direction of the RCPM, but seem to run along the connective tissue fibers (second image, clockwise).

It has been speculated that the function of the muscle dural bridge may be to prevent folding of the dura mater during hyperextension of the neck. Also, clinical evidence suggests that the muscle dural bridge may play an important role the pathogenesis of the cervicogenic headaches. The functional research of the muscle-dural bridge poses obvious difficulties, due to various reasons. Its size makes it difficult to attempt functional MR studies, although the structure has been identified in clinical MR images (figure 5.). Therefore, we are planning to perform a computer aided biomechanical simulation of this structure, which is likely to yield important data regarding its function.


Reference:

1. Hack, G.D., Koritzer, R.T., Robinson, W.L., Hallgren, R.C., Greenman, P.E.
Anatomic Relation Between the Rectus Capitis Posterior Minor Muscle and the Dura Mater
Spine 1995 (Dec); 20 (23): 2484-2486


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