Sonographic characterization of the lumbar intervertebral disk with anatomic correlation and histopathologic findings.

OBJECTIVE: The purpose of this study was to describe the normal anatomy and abnormalities of the lumbar intervertebral disk with sonography in cadaveric specimens and to correlate the sonographic findings with pathologic findings. METHODS: Sonographic imaging with both 4.5- and 10-MHz linear array transducers was performed on 35 lumbar intervertebral disks in 13 human cadaveric spines. The cadaveric specimens were sectioned for anatomic and histopathologic evaluation. Findings on anatomic sections were correlated with the findings on corresponding sonographic images with respect to the sonographic appearance of disk components in 30 intervertebral disks. RESULTS: High-resolution sonography with a 10-MHz frequency transducer enabled distinction of the nucleus pulposus from the annulus fibrosus and assessment of the echogenic characteristics of these structures. Sonography showed numerous fine linear echoes in the outer portion of the intervertebral disk in 26 (87%) of 30 specimens, which corresponded to the normal concentric arrangement of the fibers in the periphery of the annulus fibrosus. Amorphous areas of low echogenicity in the inner portion of the annulus fibrosus (n = 14, 47%) correlated with degenerative changes of the disk on corresponding microscopic sections. The nucleus pulposus appeared relatively isoechoic (n = 5, 17%) or hyperechoic (n = 4, 13%) to the annulus fibrosus. In degenerative disks (n = 21, 70%), the nucleus pulposus showed decreased echogenicity, and differentiation between the nucleus pulposus and annulus fibrosus was difficult. CONCLUSIONS: High-resolution sonography is a simple imaging method that can show the normal lumbar intervertebral disk and degenerative changes in appropriate subjects. High-resolution sonography proves superior to conventional sonography for evaluation of the lumbar intervertebral disk.