Imaging of Herniated Discs of the Cervical Spine: Inter-Modality Differences between 64-Slice Multidetector CT and 1.5-T MRI

Abstract

Objective: To assess inter-modality variability when evaluating cervical intervertebral disc herniation using 64-slice multidetector-row computed tomography (MDCT) and magnetic resonance imaging (MRI).

Materials and methods: Three musculoskeletal radiologists independently reviewed cervical spine 1.5-T MRI and 64-slice MDCT data on C2-3 though C6-7 of 51 patients in the context of intervertebral disc herniation. Interobserver and inter-modality agreements were expressed as unweighted kappa values. Weighted kappa statistics were used to assess the extents of agreement in terms of the number of involved segments (NIS) in disc herniation and epicenter measurements collected using MDCT and MRI.

Results: The interobserver agreement rates upon evaluation of disc morphology by the three radiologists were in fair to moderate agreement (k = 0.39-0.53 for MDCT images; k = 0.45-0.56 for MRIs). When the disc morphology was categorized into two and four grades, the inter-modality agreement rates were moderate (k-value, 0.59) and substantial (k-value, 0.66), respectively. The inter-modality agreements for evaluations of the NIS (k-value, 0.78) and the epicenter (k-value, 0.79) were substantial. Also, the interobserver agreements for the NIS (CT; k-value, 0.85 and MRI; k-value, 0.88) and epicenter (CT; k-value, 0.74 and MRI; k-value, 0.70) evaluations by two readers were substantial. MDCT tended to underestimate the extent of herniated disc lesions compared with MRI.

Conclusion: Multidetector-row computed tomography and MRI showed a moderate-to-substantial degree of inter-modality agreement for the assessment of herniated cervical discs. MDCT images have a tendency to underestimate the anterior/posterior extent of the herniated disc compared with MRI.

Keywords: Cervical spine; Disc herniation; MDCT; MRI.

Fig. 1. Study flow diagram

MDCT = multidetector-row computed tomography, MRI = magnetic resonance imaging, NIS = number of involved segments

Fig. 2. Schematic of seven virtual segments of C-spine for evaluation of epicenter and number of involved segments of herniated disc materials.

Two imaginary lines (*) are drawn by tracing inner margin of bilateral pedicles, and additional four lines that divide inter-pedicular space evenly are drawn. Additionally, another two lines that divide same space at lateral aspect of lines drawn along inner margin of pedicles are drawn. As result, eight virtual lines are drawn on posterior aspect of body of cervical spine, and seven segments are created.

Fig. 3. Epicenter and number of involved segments (NIS) of herniated disc on MRI.

45-year-old female with left upper extremity tingling sensation. A. T2-weighted axial imaging shows disc protrusion at C5-6 level. B. Eight virtual lines delimit seven segments, and epicenter (6) and NIS (5, 6, and 7; i.e., three segments) of herniated disc material are determined.

Fig. 4. Comparison of cervical MRI and MDCT in 43-year-old female with posterior neck pain.

Central disc protrusion is evident at C3-4 level on MRI (A, B; arrows). However, all readers interpreted disc as normal on MDCT (C, D). MDCT = multidetector-row computed tomography, MRI = magnetic resonance imaging

Fig. 5. Inter-modality agreement rates between MDCT and MRI findings at five disc levels.

Kappa values of C2-3, C3-4, C4-5, C5-6, and C6-7 disc levels are 0.67, 0.73, 0.68, 0.56, and 0.49, respectively, as depicted by central dot with whiskers, indicating upper and lower limits of 95% CIs. Decreasing trend is observed from C3-4 to C6-7 disc level. CI = confidence interval, MDCT = multidetector-row computed tomography, MRI = magnetic resonance imaging