Yonsei Med J.  2011 Jan;52(1):137-144. 10.3349/ymj.2011.52.1.137.

Comparison of Magnetic Resonance Imaging and Computed Tomography-Myelography for Quantitative Evaluation of Lumbar Intracanalar Cross-Section

• Ogura H
• Miyamoto K
• Fukuta S
• Naganawa T
• Shimizu K

• KMID: 1106448
• DOI: http://doi.org/10.3349/ymj.2011.52.1.137

Abstract

PURPOSE
A comparison of MRI and computed tomography-myelography (CTM) for lumbar intracanalar dimensions. To compare the capability and reproducibility of MRI and CTM in measuring the cross-sectional morphology of intracanalar lesions of the lumbar spine.
MATERIALS AND METHODS
MRI and CTM of lumbar disc levels from 61 subjects with various lumbar spinal diseases were studied. Dural area, dural anteroposterior (AP) diameter, dural right-left diameter, and thickness of the ligamentum flavum were measured by two orthopedic surgeons. Each section was graded by degree of stenosis. Absolute value and intra- and inter-observer correlation coefficients (ICC) of these measurements and the associations between MRI and CTM values were determined.
RESULTS
Except for MRI determination of ligament flavum thickness, CTM and MRI and intra- and ICC suggested sufficient reproducibility. When measurements of dural area, dural AP diameter, and RL diameter were compared, values in CTM were significantly (p = 0.01-0.004) larger than those in MRI (CTM/MRI ratios, 119%, 111%, and 105%, respectively). As spinal stenosis became more severe, discrepancies between CTM and MRI in measurements of the dural sac became larger.
CONCLUSION
Both CTM and MRI provided reproducible measurements of lumbar intracanalar dimensions. However, flavum thickness may be more accurately measured by CTM. Because the differences in the measurements between CTM and MRI are very slight and there is very little data to suggest that the precise degree of stenosis is related to symptoms or treatment outcome, the usefulness of the CTM over MRI needs to be confirmed in future studies.

Keyword

Magnetic resonance imaging; computed tomography; myelography; CTM; lumbar spine; lumbar spinal canal stenosis; diagnosis

MeSH Terms

Aged
Aged, 80 and over
Female
Humans
Lumbar Vertebrae/*pathology/*radiography
Magnetic Resonance Imaging/*methods
Male
Middle Aged
Myelography/*methods
Spinal Stenosis/*pathology/*radiography
Tomography, X-Ray Computed/*methods

Figure

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  Fig. 1 Grades of stenosis severity by MRI and CTM.

• 

  Fig. 2 Measurements of intracanalar morphology using magnetic resonance imaging (MRI, left) and computed tomography-myelography (CTM, right). (A) Dural area: Cross-sectional area of the dural sac. (B) Dural AP diameter: Maximum anteroposterior diameter of the dural sac. (C) Dural RL diameter: Maximum right-left diameter of the dural sac. (D) Ligamentum flavum thickness: Thickness of the ligamentum flavum at its thickest part on the right and left. AP, anteroposterior; RL, right-left.

• 

  Fig. 3 Average measurements of dural area, dural AP and RL distance, and flavum thickness in each grade of stenosis severity. (A) Dural area: MRI measurements were significantly smaller than CTM measurements for total levels and grades 1 and 2. More severe stenosis was significantly correlated with a smaller cross sectional area of the dural sac in both CTM and MRI (one-factor ANOVA, p < 0.001). (B) Dural AP diameter: MRI measurements were significantly smaller than CTM measurements for total levels and grades 1 and 2. (C) Dural RL diameter: MRI measurements were significantly smaller than CTM measurements for total levels and grades 1 and 2. (D) Flavum thickness: CTM measurements of flavum thickness were significantly smaller than MRI measurements for total levels and grades 1 and 3. AP, anteroposterior; RL, right-left.

• 

  Fig. 4 Simple regression of dural area in MRI and CTM by stenosis grade: For grades 1 and 2, there were significant correlations between MRI and CTM, with high R2 values (p < 0.01 each). For grade 3, however, R2 was very low.

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  Fig. 5 Typical examples of discrepancies between CTM and MRI in severe stenotic levels. (A) In the MRI, the dural sac could be confirmed. In the CTM, however, dural shape and ligamentum flavum could not be observed. (B) On the MRI, the dural sac is boomerang-shaped with compression by a herniated disc. On the CTM, however, the shape of the dural sac is altered as it becomes partially filled with contrast medium.

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