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Accurate Identification of Disc Material Critical for Preoperative Planning

January 21, 2008
Written by: , Filed in: Neuroradiology
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Angled axial images are believed to be more sensitive for detection of disc herniations, although no data exist in the literature. Angled images typically are limited to the disc space with resultant image gaps. Sagittal images are assumed to be enough to compensate for those gaps.

The objective of a recent study was to compare sensitivities of contiguous axial images with disc space-targeted angled images of the lumbar spine for detection of spondylolysis defects and disc sequestra.

The study has concluded that as migrated disc material can lie above or below the disc space, contiguous axial images should be performed to increase the detection rate.


Prospective imaging was done in 103 patients with targeted disc space.

Contiguous axial images (spin-echo [SE] T1 and fast spin-echo [FSE] T2) in addition to sagittal SE-T1- and fat-suppressed FSE-T2-weighted images were taken.

Sagittal images were combined with axial images and were read separately with a time delay; researchers were blinded to the initial interpretation. On discordant readings, a consensus was reached.

Neuroradiology Review

The Johns Hopkins University School of Medicine
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In the continuous axial dataset, spondylolysis was identified in 14 patients at 15 levels (14%). The pars defects were bilateral in 14 of those 15 cases; 50% had spondylolisthesis. Twelve patients (12%) had migrated disc material, which was midline in 4 and off midline in 8. In the disc-targeted image set, pars defects were found in 8 patients (7%); all were bilateral.

Spondylolisthesis was found in 50%. Migrated disc material was found in 3 patients (3%), off midline in 2 and 1 in midline. All disc sequestra detected in targeted disc images were seen on contiguous axial images. However, in 9 of 12 cases, migrated disc material was missed on targeted images.

Nine pars defects were not seen on targeted images. However, 2 pars defects were not seen on contiguous images but were found on targeted images.

The difference in sensitivity comparing both protocols was statistically significant (P =0.016). There was a trend toward decreased sensitivity for diagnosis of spondylolysis defects, but it did not reach statistical significance (P =0.12).

Contiguous axial images are more sensitive than axial angled images for detection of migrated disc material and spondylolysis defects.

Reviewer’s Comments
Sagittal images alone are faulty in diagnosing pars defects, which has been documented in the literature by Johnson et al (AJR 1989, 152; 327-332).

Spondylolysis defects can be a significant cause of lower back pain. Often patients do not have correlative imaging, such as plain films or CT, so missing that diagnosis may have a negative impact on patient treatment.

Sagittal images can result in both false-positive and false-negative diagnoses of disc sequestra, especially with lateral location of the disc fragment, which occurs in a majority of cases, due to a midline septum. Accurate identification of extruded disc material is critical for preoperative planning.

Author: : Cornelia Wenokor, MD
Reference: :
Singh K, Helms CA, et al. Disc Space-Targeted Angled Axial MR Images of the Lumbar Spine: A Potential Source of Diagnostic Error.
Skeletal Radiol; 2007; 36 (December): 1147-1153

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