Comparison of [18F] FDG-PET/MRI and Clinical Findings for Assessment of Suspected Lumbar Facet Joint Pain: A Prospective Study to Characterize Candidate Nonanatomic Imaging Biomarkers and Potential Impact on Management

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Ten patients with clinically suspected facetogenic low back pain were prospectively recruited with a designation of specific facet joints implicated clinically. Subsequently, patients underwent an FDG-PET/MR imaging examination with gadolinium. Each facet joint was graded for perifacet signal change on MR imaging and FDG activity. The frequency and correlation of MR imaging, FDG-PET, and clinical findings were determined. There was low concordance of perifacet signal change and FDG activity with clinically implicated facet joints. This could indicate either the potential to change patient management or a lack of biomarker accuracy.

Abstract

Clinical concordance of the sides of pain and imaging findings, but discordance of specific implicated facet joints. Clinically, this patient had bilateral low back pain and had been prescribed bilateral L4–L5 and L5–S1 facet joint injections. There were high-grade MR imaging scores and increased FDG activity of the bilateral L3–L4 facet joints, but not of the bilateral L4–L5 or L5–S1 facet joints. Sagittal fat-suppressed T1-weighted image with gadolinium demonstrates high-grade perifacet enhancement of the left L3–L4 facet joint (arrow), but not of the L4–L5 or L5–S1 facet joints (A). Sagittal FDG-PET and fused PET/MR images (B and C) also demonstrate increased L3–L4 perifacet FDG activity (arrows). Note that the FDG activity is distinguishable from areas of vascular enhancement but is not visually increased in the area of L3 pedicle enhancement (arrowhead in D and E). The perifacet signal change of the bilateral L3–L4 facet joints on axial fat-suppressed T2-weighted images is identified (arrows, D) but is more apparent on axial fat-suppressed T1-weighted images with gadolinium (arrows, E). An axial fused PET/MR image also demonstrates increased perifacet FDG activity of the bilateral L3–L4 facet joints (arrows, F).

BACKGROUND AND PURPOSE

Prior retrospective studies have suggested that both T2 hyperintensity and gadolinium enhancement on fat-suppressed MR imaging are associated with lumbar facet joint pain, but prospective evaluation of FDG-PET/MR imaging with a standardized protocol and correlation to clinical findings are lacking. The primary aim was to prospectively assess a standardized FDG-PET/MRI protocol in patients with suspected facetogenic low back pain, with determination of the concordance of imaging and clinical findings.

MATERIALS AND METHODS

Ten patients with clinically suspected facetogenic low back pain were prospectively recruited with a designation of specific facet joints implicated clinically. Subsequently, patients underwent an FDG-PET/MR imaging examination with gadolinium. Each facet joint was graded for perifacet signal change on MR imaging and FDG activity. The frequency and correlation of MR imaging, FDG-PET, and clinical findings were determined.

RESULTS

FDG activity showed high concordance with high overall MR imaging scores (concordance correlation coefficient = 0.79). There was concordance of the clinical side of pain with the side of high overall MR imaging scores and increased FDG activity on 12/20 (60%) sides. Both a high overall MR imaging score (concordance correlation coefficient = 0.12) and FDG-PET findings positive for increased activity (concordance correlation coefficient = 0.10) had low concordance with the specific clinically implicated facet joints. Increased FDG activity or high MR imaging scores or both were present in only 10/29 (34%) facet joints that had been clinically selected for percutaneous intervention. Eleven (11%) facet joints that had not been selected for treatment demonstrated these imaging findings.

CONCLUSIONS

There was low concordance of perifacet signal change and FDG activity with clinically implicated facet joints. This could indicate either the potential to change patient management or a lack of biomarker accuracy. Therefore, additional larger randomized studies with the use of comparative medial branch blocks would be useful to further investigate the clinical utility of these findings.

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