RADIOLOGICAL SOCIETY OF NORTH AMERICA 2003 (RSNA): Scientific Papers
Neuroradiology/Head and Neck (My Aching Back)

POSTURAL VARIATION IN DURAL SAC CROSS SECTIONAL AREA MEASURED IN NORMAL INDIVIDUALS SUPINE, STANDING, AND SITTING, USING pMRI

DATE: Thursday: December 04, 2004
START TIME: 11:40 AM
END TIME: 11:47 AM
LOCATION: ROOM N228
CODE: Q13-1316

PARTICIPANTS PRESENTER
Francis W. Smith, MD
University of Aberbeen, Scotland, U.K.

CO-AUTHOR
Yoichiro Hirasawa MD
Waseem Bashir MBBS
Malcolm Pope PhD

Keywords: Spinal canal

PURPOSE
Clinical symptoms in lumbar spinal stenosis are posture-related. Pain and numbness in the buttock and leg are often provoked either by walking or by prolonged standing. Symptomatic relief may be obtained by lying and sitting. It is well known that the available space within the lumbar spinal canal decreases with extension, axial loading, and increases in flexion. The unique design of Position MRI allows patients to be scanned whilst standing, sitting or lyijng down. This facilitates imaging in postures where patients report discomfort. Before this new capability is applied to diagnosis, the relationship between dural sac cross sectional area and lumbar posture in normal individuals must be ascertained.

METHODS AND MATERIALS
29 male volunteers, with no symptoms of low back pain or sciatica, were recruited for this study. The mean age was 32.9 years (21-61). Prior to imaging each individual lay for 20 minutes in the supine position before studied with pMRI using a 0.6T FONAR Indominitable Stand-up MRI scanner. Data was collected in the supine, standing, simple sitting, sitting flexion and sitting extension positions. Cross sectional area of the dural sac and diameter of the dural sac, in both sagittal and axial images were measured at the level of the disks at L3/4, L4/5 and L5/S1 on pMRI images, by two trained observers.

RESULTS
Statistically significant positional dependence of the dural sac diameter was found at the L3/4, L4/5 and L5/S1 levels. The smallest dural sac dimensions were found in the supine position. The greatest area was found in the sitting flexed position. In the erect posture the area was less than sitting in neutral or flexion. Sitting in extension was found to have a smaller area than sitting in flexion. The difference in the cross-sectional area was also statistically significant in each posture at all levels studied. The supine posture gave the smallest cross-sectional area compared to sitting in flexion and in extension.

CONCLUSION
Alterations in the dimensions of the dural sac can be observered and accurately measured in different postures, using pMRI. This information will be useful for the examination and management of patients sufferijng from lumbar spinal canal stenosis.