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MRI of the Lumbar Spine: A Sports Medicine Approach - page 3 / 4

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fat signal seen in adults, the marrow may be bright on a T2 weighted sequence and de- creased in signal on a T1 weighted sequence. Modic first described this MRI finding, and it is called Modic Type 1 change. The finding is due to granulation tissue (not just edema), and therefore much as the granulation tissue around a disc extrusion will enchance after intravenous contrast.

If the signal is dark on T2 and bright on T1 (typical of complete fatty replacement), then this is termed Modic Type 2. There is evidence that Type 1 change is specific for discal pain and perhaps instability [15,18,28,30]. A recent study indicated that moderate end plate changes of both Type 1 and Type 2 may show a high correlation with discogenic pain [42]. Similar inflammatory marrow changes may be seen adjacent to Schmorl´s nodes [26,32,33,34]. It may be that there is a progression from Type 1 to Type 2 as the spine restabilizes, or in the case of spinal fusions, the fusion becomes solid. It is also possible for Type 2 to revert to Type 1 with interval destabilization.

SPINAL STENOSIS

Lumbar spinal central stenosis may be divided into developmental and acquired. Almost all central stenosis is due to developmental stenosis with short pedicles and relatively large facets; or degenerative spondylolisthesis. Developmental central stenosis alone is unlikely symptomatic, but lessens the “reserve“ necessary to protect against central stenosis when the disc and posterior elements degenerate. As the facet joints degenerate there is a decrease in the interfacet angle and often flattening of the posterior thecal sac from the noncompliant posterior epidural fat pad. Absolute measurements of the diameter or cross sectional area of the central canal are of less importance than the observation of the effect on the thecal sac and nerve roots. We

Developmental Central Stenosis

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MRI of the Lumbar Spine

Up-Down Foraminal Stenosis with swollen L5 nerve root

categorize stenosis by quarters: <25% cross sectional loss – mild; 25-50% – moderate; 50-75% – moderately severe; and >75% severe.

The anatomic area from the exit of the nerve root from the thecal sac until the entrance zone of the foramen is termed the lateral recess. In reality, lateral recess stenosis is almost always a result of facet hypertrophy, and the area narrowed is therefore the “subarticular gutter“ which is the most cranial portion of the lateral recess.

Foraminal or lateral stenosis is almost al- ways a result of loss of disc height and posterolateral osseous ridging secondary to annular bulging. These findings narrow the foramen in an “up-down“ or “cranio- caudal“ fashion, entrapping the exiting nerve root between the posterolateral ridge and the undersurface of the pedicle. Less commonly isolated overgrowth of enlarged facet joints and facet capsular hypertrophy results in isolated “front-back“ or “ventro- dorsal“ foraminal stenosis. A combination of both types of lateral stenosis would be termed concentric foraminal narrowing. As with disc extrusions, pre or post compressive nerve root swelling may be seen with central and foraminal stenosis.

SUMMARY

The knowledge of normal and intradiscal anatomy demonstrated by MRI has grown exponentially over the last few years. While the significance of some findings is clear cut, especially in the evaluation of radiculopathy, in the study of discogenic pain, controversies still exist. As with all imaging studies, the comparison of MRI findings with the clinical evaluation is always essential.

Jay A. Kaiser MD jkaiser@immixmgt.com

Imaging of the Spine Bibliography (March 23, 2001)

[1] Ito, M et al Predictive Signs of Discogenic Lumbar Pain on Magnetic Resonance Imaging with Discography Correlation. 1998 Spine 23, Number 11, 1252-1260.

[2] Yu S, et al. Comparison of MR and discography in detecting radial tears of the annulus: A postmortem study. Am J Neuroradiol 1989:10: 1077-81.

[3] Yu S., et al. Tears of the annulus fibrosus: Correlation between MR and pathologic findings in cadavers. Am J. Neuroradiol 1988; 9: 367-70.

[4] Aprill C, Bogduk N. High-intensity Zone: A diagnostic sin of painful lumbar disc on magnetic resonance imaging. Br. J. Radiol 1992; 65: 361- 69.

[5] Ricketson R, Simmons JW et al. The prolapsed intervertebral disc: the high intensity zone with discography correlation. Spine 1996; 21: 2758-

62. [6] Schellhas KP et al

. Lumbar disc high intensity

zone: Correlation of magnetic resonance imaging and discography. Spine 1996; 21:79-86.

[7] Buirski, G. Magnetic resonance signal patterns of lumbar discs in patients with low back pain. Spine 1992; 17: 1199-2004.

[8] Bogduk, N. Point of View Spine 1998; 23:11; 1259-1260.

[9] Saifuddin A S et al. The Value of Lumbar Spine Magnetic Resonance Imaging in the Demonstration of Annular Tears. Spine 1998; 23; 4: 453-457.

[10] Stadnik TW et al. Annular tears and disk herniation: prevalence and contrast enhancement on MR images in the absence of low back pain or

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