Development of Lumbar High Intensity Zone on Axial Loaded Magnetic Resonance Imaging

ⓒ 2003 Lippincott Williams & Wilkins, Inc.

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Volume 28(21)             1 November 2003             pp E449-E451

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[Case Report]

Saifuddin, Asif FRCR*; McSweeney, Emer FRCR*; Lehovsky, Jan FRCS(I), MCh, Orth.↕

From *Wide Open MRI of North London, London, and the

↕Department of Spinal Deformity, The Royal National Orthopaedic Hospital Trust, Middlesex, United Kingdom.

Acknowledgment date: February 13, 2003.

First revision date: April 17, 2003.

Acceptance date: June 6, 2003.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence to Dr. A. Saifuddin, Consultant Radiologist, The Royal National Orthopaedic Hospital Trust, Brockley Hill, Stanmore HA7 4LP, England; E-mail: ASaifuddin@aol.com

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Abstract

Study Design. Case report.

Objectives. To report the development of high intensity zones in the lumbar posterior anulus on axial loaded magnetic resonance imaging.

Summary of Background Data. The high intensity zone is seen in the posterior anulus of degenerate lumbar discs on T2-weighted magnetic resonance images and represents a radial anular tear. Although the specificity of the high intensity zone for a concordantly painful anular tear in patients undergoing discography for discogenic low back pain is high, the sensitivity of magnetic resonance imaging for identification of discographically demonstrated anular tears is approximately 30%.

Methods. A 55-year-old female with chronic low back pain was imaged with lumbar spine magnetic resonance imaging before and following axial loading with an magnetic resonance imaging-compatible compression device.

Results. The nonloaded study demonstrated degeneration of the lower four lumbar discs. Following axial loading, posterior central high intensity zones were identified at the L2-L3 and L4-L5 levels.

Conclusion. High intensity zones developed on axial loaded magnetic resonance imaging of the lumbar spine. We postulate that lumbar spine magnetic resonance imaging with axial loading may increase the sensitivity of magnetic resonance imaging for the detection of high intensity zones.

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The high intensity zone (HIZ) was first described by Aprill and Bogduk on sagittal T2-weighted (T2W) magnetic resonance imaging (MRI) studies of the lumbar spine in patients with chronic low back pain. 1 The HIZ is defined as a focal area of high signal intensity (SI) within the posterior anulus of a degenerate disc, separated from and of higher SI compared to the disc nucleus. 1 Although in the original report, the HIZ was described as being seen mainly in the midline, 1 it is also known that it can occur in the posterolateral anulus. 2 Comparison studies with lumbar discography suggest that the HIZ is associated with concordant pain reproduction on disc injection, 3?7 although the exact nature of the HIZ is not fully understood. A Grade 3 to 4 radial anular tear is always present on injection of a disc containing a HIZ, leading Aprill and Bogduk to postulate that the HIZ is a marker of a radial anular tear. 1 The high SI of the lesion suggests that it at least partly represents fluid within cavities in the outer anulus. 8 However, a large proportion of HIZs show enhancement following intravenous contrast administration, indicating the presence of associated vascular granulation tissue. 9

Not all discographically demonstrated anular tears are manifest at MRI as a HIZ. 1,4 The reason for this is not known. We present a case in which HIZs were identified in a patient only after axial loading with an MRI-compatible compression device.

Case Report

A 55-year-old female presented with a history of long standing low back pain. The symptoms were progressive over the previous 4 years. The pain was located in the low back with radiation to the left hip, groin, and lower limb. Examination revealed no neurologic deficit. Radiographs demonstrated a mild degenerative lumbar scoliosis. Magnetic resonance imaging studies identified disc degeneration at the lower four lumbar disc levels. She was initially managed with a combination of oral analgesia and facet joint injections, which resulted in approximately 20% to 30% improvement in her low back pain.

Due to progressive symptoms, a further MRI study was performed. The patient was imaged in a low field open MR scanner at 0.3 Tesla, with the following imaging parameters for the T2-weighted sequences: sagittal T2-weighted fast spin echo sequence; TR 3100 ms, TE 125 ms, slice thickness 4.5 mm, interslice gap 1.0 mm, matrix 256 × 256: axial T2-weighted fast spin echo sequence; TR 3900 ms, TE 125 ms, slice thickness 4.0 mm, interslice gap 1.0 mm, matrix 256 × 256. The lumbar spine was then loaded to 50% of the patients body weight for 5 minutes with an MRI-compatible compression device as previously described (Dynawell, Dynamed AB, Stockholm, Sweden) 10 and reimaged with the same imaging sequences and parameters as the nonloaded study. Nonloaded T2W images demonstrated degeneration of the lower four lumbar discs as before. Following axial loading, HIZs developed at the L2-L3 and L4-L5 levels (Figure 1). Review of previous discogram reports confirmed the presence of radial anular tears at these two discs, with the production of concordant pain responses at both levels.

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Figure 1. T2-weighted spin echo lumbar spine MRI. A, Mid-line sagittal image before application of axial loading. The lower four lumbar discs are degenerate. No HIZ is evident. B, Mid-line sagittal image following application of axial loading showing the development of HIZs at the L2-L3 and L4-L5 levels. C, Axial image at the L2-L3 level before axial loading. D, Axial image at the L2-L3 level following axial loading showing a linear central HIZ. Note also contour change of the posterior disc margin, which becomes convex.

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Discussion

Yu et al8 have described three types of anular tears of the lumbar disc, of which the radial tear is implicated as a source of discogenic low back pain. The radial anular tear is the commonest and most specific pathologic discographic finding in patients with concordant low back pain at discography. 11

Radial anular tears are optimally imaged with computed tomographic (CT) discography. 12 The tear itself is typically not identified by standard MR techniques but is manifest as the HIZ. 1 Discography of discs containing a HIZ reveals the presence of a radial anular tear, with early studies suggesting that the HIZ was a highly specific marker of a painful disc. 1?7 However, later studies report that the HIZ can be identified in the absence of low back pain 13,14 and is not associated with any particular group of clinical symptoms. 2 The true relevance of the HIZ in patients with low back pain is, therefore, unclear.

Aprill and Bogduk 1 have suggested that the HIZ represents displaced nuclear material within the posterior anulus, which becomes hyperintense due to associated inflammation. Although all discs containing a HIZ will show a radial anular tear at discography, many discographically demonstrated anular tears are not identified as the HIZ. 1,4 The reason for this is not known.

Axial loaded MRI was developed with the aim of simulating lumbar spine imaging in the upright position. Loading the patient to 50% of body weight for 5 minutes produces forces at the L3?L4 disc level, which are equivalent to the effect of gravity on the lumbar spine with the patient standing. 10 The effect on morphology of the normal and degenerate disc has not been clarified, although alterations in disc height and increase in lumbar lordosis are seen, 15 and lordosis has been shown to alter the position of the nucleus pulposus. 16 Magnetic resonance imaging with axial loading is of value in the demonstration of occult nerve root compression in patients with neurogenic claudication or sciatica. 17 However, its potential role in the setting of low back pain has not been investigated.

We have presented a case of a patient with chronic low back pain and multilevel disc degeneration on conventional T2-weighted MRI, whose loaded MRI study demonstrated the development of HIZs at the L2?L3 and L4?L5 disc levels on both the sagittal and axial images. Review of a previous discography report indicated that radial anular tears were present at these disc levels. We postulate that changes in intradiscal pressure and anular stresses, which occur with axial compression, 18 resulted in fluid being forced through a radial anular tear to fill a cavity in the outer anulus, as can be seen during CT discography. Although the addition of axial loading allowed identification of the HIZs, the relationship of this finding to the patient’s symptoms is unclear. However, these findings suggest that axial loaded MRI may increase the detection of the HIZ compared to conventional MRI, although a prospective study with a large number of patients comparing nonloaded with axial loaded T2-weighted MRI and discography would be required to test this hypothesis.

Key Points

* Radial anular tears are manifested as the HIZ on MRI.

* Magnetic resonance imaging has a high specificity but low sensitivity for the detection of anular tears.

* High intensity zones were demonstrated at two disc levels on axial loaded MRI but were not seen on the nonloaded study.

* Axial loaded MRI may increase the sensitivity of MRI for detection of anular tears.

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