Peripheral focal low signal intensity areas in the degenerated annulus fibrosus on T2-weighted fast spin echo MR images: correlation with macroscopic and microscopic findings in elderly cadavers

Morphology of the cartilaginous endplates in human intervertebral disks with ultrashort echo time MR imaging

PURPOSE

To image human disk-bone specimens by using conventional spin-echo (SE) and ultrashort echo time (TE) techniques, to describe the morphology at magnetic resonance (MR) imaging, and to identify tissue components contributing to high signal intensity near the cartilaginous endplates (CEPs).

MATERIALS AND METHODS

This study was exempt from institutional review board approval, and informed consent was not required. Five cadaveric lumbar spines (mean age, 61 years ± 11) were prepared into six sample types containing different combinations of disk, uncalcified CEP, calcified CEP, and subchondral bone components and were imaged with proton density-weighted SE (repetition time msec/TE msec, 2000/15) and ultrashort TE (300/0.008, 6.6, echo-subtraction) sequences. Images were evaluated to determine the presence of intermediate-to-high signal intensity in regions excluding the bone marrow. Logistic regression was used to determine which tissue components were significant predictors of the presence of signal intensity for each MR technique.

RESULTS

On ultrashort TE MR images, intact disk/uncalcified CEP/calcified CEP/bone samples exhibited bilaminar intermediate-to-high signal intensity in the region near the CEP, consistent with the histologic appearance of uncalcified and calcified CEPs. Conversely, proton density-weighted SE images exhibited low signal intensity in this region. Results of logistic regression suggested that the presence of uncalcified CEP (P = .023) and calcified CEP (P = .007) in the sample were strong predictors of the presence of signal intensity on ultrashort TE images, whereas the disk was the only predictor (P < .001) of signal intensity on proton density-weighted SE images.

CONCLUSION

Ultrashort TE imaging, unlike proton density-weighted SE imaging, enabled direct visualization of the uncalcified and calcified CEP. Evaluation of the morphology and identification of sources of signal intensity at ultrashort TE MR imaging provides opportunities to potentially aid in the understanding of degenerative disk disease.

Imaging of disk disease and degenerative spondylosis of the lumbar spine

Low back pain is a common but poorly understood entity. Features of degeneration depend on which component of the motion segment is predominantly affected, and include disk space narrowing, vacuum phenomenon, disk desiccation, vertebral osteophyte formation, disk herniation, and facet arthrosis, but these features do not necessarily have any relationship to symptoms. Since most episodes of back pain resolve on their own, and most disk herniations spontaneously regress, imaging of low back pain, although widely performed, is probably not necessary in most cases.

The lumbar vertebral body and diskovertebral junction. Radio MR imaging anatomic correlations

Radiographs and MR images of spine specimens provide superb tomographic views of changes that involve the mineralized network and the medullary content of vertebral bodies. By illustrating changes in the balance between bone resorption and formation and between fat and nonfat marrow cells, these frozen images of the reality help us to understand normal variants and lesions that develop in osseous and articular diseases of the lumbar spine.