Anterior commissure: anatomic-MR correlation and use as a landmark in three orthogonal planes

Correlation of cryomicrotomic and myelin-stained sections of human cadaver heads with spin-echo magnetic resonance (MR) images documents that MR imaging routinely displays the anterior commissure in three orthogonal planes as a distinct white-matter tract that resembles bicycle handlebars. The anterior commissure crosses the midline at the upper end of the lamina terminalis, just anterior to the anterior columns of the fornices. To each side of midline, it curves antero-inferolaterally and then postero-inferolaterally through the lateral nucleus of the globus pallidus to course with the white matter of the external and extreme capsules toward the middle and inferior temporal gyri. Because the anterior commissure is easily recognizable in all three planes at differing pulse sequences, the commissure has proved to be a major landmark for identification of the complex anatomy of this region, especially in sagittal sections.     

Effect of chymopapain on the meninges studied in an experimental model

The effect of chymopapain and contrast media in the epidural space on meninges has not been studied conclusively. The authors injected chymopapain into the epidural space of monkeys and measured the degree of arachnoid fibrosis that resulted. Animals were given injections of 1.2 mL of diatrizoate (280 mg iodine per milliliter), chymopapain (100 IU/mL), kaolin (100 mg/mL) (as a positive control), or saline (0.9%) (as a negative control). Three months later the animals were killed; the dural sac was removed intact and was fixed, sectioned, stained, and examined with light microscopy. Kaolin-treated animals developed mild to marked fibrosis of the dura. The saline- and diatrizoate-treated animals developed little or no evidence of fibrosis. One of four chymopapain-treated animals developed degenerative changes in dorsal nerve roots and fibrosis in the adjacent arachnoid. The other chymopapain-treated animals had little or no evidence of fibrosis. The studies suggest that neither diatrizoate nor chymopapain causes arachnoid fibrosis.     

T1 and T2 measurements on a 1.5-T commercial MR imager

In order for relaxation times to be used in clinical diagnosis, the precision of the measurement must be determined. The authors measured T1, T2, and proton density in a phantom and in human volunteers to determine the reproducibility of the method. The coefficient of variance of T1 measurements in the phantom during a 15-month period with two software upgrades was 5%. Variance of T2 measurements with any given software was 4% or less, and overall in the 15-month period, with two software changes, the T2 reproducibility was between 6% and 9%. The reproducibility is sufficiently high that precise clinical measurements of T1, T2, and proton density are feasible.     

Effect of axial loading on neural foramina and nerve roots in the lumbar spine

The hypothesis that the neural foramina in some patients are critically narrowed by axial compression of the spine has not been studied with direct imaging techniques. Frozen cadaveric motion segments of the lumbar spine (intervertebral disk and contiguous vertebrae) were imaged with computed tomography (CT). The segments were thawed and compressed in a hydrostatic press to simulate axial loading, and then the segments were frozen and imaged again. The motion segments were subsequently sectioned with a cryomicrotome, and the chronic degenerative changes present in the disks were classified. Pre- and post-compression CT images were compared, and anatomic relationships were studied. In 41 randomly selected segments (some with preexisting radial, transverse, and concentric annular tears), compression diminished the diameters and cross-sectional areas of the spinal canal and neural foramina. In no cases were nerve roots displaced, distorted, or compressed by axial loading. This study suggests that axial loading, such as that produced by ordinary weight bearing, does not critically compromise the neural foramina even in the presence of chronic degenerative disk changes.