Confidence in Assessment of Lumbar Spondylolysis Using Three-Dimensional Volumetric T2-Weighted MRI Compared With Limited Field of View, Decreased-Dose CT

Abstract

Background: Limited z-axis-coverage computed tomography (CT) to evaluate for pediatric lumbar spondylolysis, altering the technique such that the dose to the patient is comparable or lower than radiographs, is currently used at our institution. The objective of the study was to determine whether volumetric 3-dimensional fast spin echo magnetic resonance imaging (3D MRI) can provide equal or greater diagnostic accuracy compared with limited CT in the diagnosis of pediatric lumbar spondylolysis without ionizing radiation.

Hypothesis: Volumetric 3D MRI can provide equal or greater diagnostic accuracy compared with low-dose CT for pediatric lumbar spondylolysis without ionizing radiation.

Study design: Clinical review.

Level of evidence: Level 2.

Methods: Three pediatric neuroradiologists evaluated 2-dimensional (2D) MRI, 2D + 3D MRI, and limited CT examinations in 42 pediatric patients who obtained imaging for low back pain and suspected spondylolysis. As there is no gold standard for the diagnosis of spondylolysis besides surgery, interobserver agreement and degree of confidence were compared to determine which modality is preferable.

Results: Decreased-dose CT provided a greater level of agreement than 2D MRI and 2D + 3D MRI. The kappa for rater agreement with 2D MRI, 2D + 3D MRI, and CT was 0.19, 0.32, and 1.0, respectively. All raters agreed in 31%, 40%, and 100% of cases with 2D MRI, 2D + 3D MRI, and CT. Lack of confidence was significantly lower with CT (0%) than with 2D MRI (30%) and 2D + 3D MRI (25%).

Conclusion: For diagnosing spondylolysis, radiologist agreement and confidence trended toward improvement with the addition of a volumetric 3D MRI sequence to standard 2D MRI sequences compared with 2D MRI alone; however, agreement and confidence remain significantly greater using decreased-dose CT when compared with either MRI acquisition.

Clinical relevance: Decreased-dose CT of the lumbar spine remains the optimal examination to confirm a high suspicion of spondylolysis, with dose essentially equivalent to radiographs. If clinical symptoms are not classic for spondylolysis, 2D MRI is still very good at detecting spondylolysis while remaining sensitive for detection of alternative diagnoses such as disc abnormalities and pars stress reaction. The data suggest that standard 2D MRI sequences should not be entirely replaced by a volumetric T2-weighted 3D sequence (despite promising features of rapid acquisition time, increased spatial resolution, and reconstruction capability).

Keywords: 2D MRI; 3D MRI; CT; spondylolysis; volumetric.

Figure 1.

(a) Kappa values for computed tomography (CT) compared with magnetic resonance imaging (MRI). (b) Rater agreement and lack of certainty.

Figure 2.

Bilateral L5 pars defects are more conspicuous on decreased-dose CT (a, c) compared with 2-dimensional (2D) MRI T1-weighted sequences (b, d). The conventional 2D MRI was obtained a few weeks before the CT, and only the left defect (d, white arrow) was initially detected on the sagittal T1-weighted sequence. (b) The right pars was called intact on MRI. CT clearly shows bilateral L5 defects (a, c, black arrows), and in hindsight, the right defect becomes more apparent on MRI (b, white arrow). CT, computed tomography; MRI, magnetic resonance imaging.

Figure 3.

In order of confidence level for detecting left L5 spondylolysis (white arrows), (a) decreased-dose CT was favored over (b) the 2D MRI T1-weighted sequence, which was favored over (c) the 3D MRI T2-weighted sequence. 2D, 2-dimensional; 3D, 3-dimensional; CT, computed tomography; MRI, magnetic resonance imaging.

Figure 4.

Right L5 pars defect (white arrows) in a patient with a lumbosacral hemivertebra and distorted anatomic planes. In order of confidence level for detecting spondylolysis (a) decreased-dose CT was favored over (b) the 2D MRI T1-weighted sequence, which was favored over (c) the 3D MRI T2-weighted sequence. 2D, 2-dimensional; 3D, 3-dimensional; CT, computed tomography; MRI, magnetic resonance imaging.

Figure 5.

(a, b) Right and (c, d) left L5 pars defects (white arrows). Although improved spatial resolution with 3D MRI T2-weighted sequences would theoretically improve detection of spondylolysis, all raters favored the 2D MRI T1-weighted sequence (a, c) over 3D images (b, d), likely related to improved contrast resolution. 2D, 2-dimensional; 3D, 3-dimensional; CT, computed tomography; MRI, magnetic resonance imaging.

Figure 6.

(a, b, c) Right and (d, e, f) left L5 pars defects. The defects (white arrows) are best defined on the 2D MRI T1-weighted sequence (a, d) compared with the 2D STIR sequence (b, e) and 3D T2-weighted sequence (c, f). An advantage of MRI over CT (not obtained in this case) is identification of edema associated with the left defect (e, red arrowheads), indicating a subacute or symptomatic defect, compared with the nonedematous chronic right defect (b). MRI is also helpful in detecting pars stress reaction, which may be symptomatic prior to the appearance of a defect on CT. 2D, 2-dimensional; 3D, 3-dimensional; CT, computed tomography; MRI, magnetic resonance imaging; STIR, short tau inversion recovery.