AJR: MRI may be cheaper, rad-free method of lymphoma staging
Whole body diffusion-weighted MRI in lymphoma patients may yield staging results largely equal to those of the standard 18F-FDG PET/CT, while delivering no radiation and a more economical alternative, according to a study published in the March issue of the American Journal of Roentgenology. However, further studies are required to confirm the role of MRI.

“FDG PET/CT is currently regarded as the reference standard in the staging of high-grade lymphoma,” though bone marrow biopsy is still considered mandatory, explained Henriëtte M. E. Quarles van Ufford, MD, from the department of radiology at University Medical Center Utrecht, in Utrecht, the Netherlands, and co-authors.

However, van Ufford and colleagues pointed out that 18F-FDG PET/CT is both a radiation-inducing and high-cost procedure, relative to whole-body MRI. The authors therefore sought to compare the two modalities in the staging of lymphoma, looking at interobserver agreement of T1-weighted, short T1 inversion recovery (STIR) and diffusion-weighted (DWI) MRI. Twenty-one patients newly diagnosed with lymphoma underwent all three procedures plus 18F-FDG PET/CT.

Whole-body MRI-DWI staging equaled that of FDG PET/CT in approximately 75 percent of patients, delivering an interobserver agreement (kappa value) of 0.597 and 0.507 for all nodal and extranodal regions together, respectively. Kappa values for interobserver agreement for two observers between all MRI-DWI staging was 0.676 and 0.452 for all nodal regions and all extranodal regions, respectively.

MRI-DWI overstaged findings relative to FDG PET/CT in five of 22 cases, though it never understaged relative to FDG PET/CT. “Importantly, whole-body MRI-DWI overstaging relative to FDG PET/CT was clinically relevant in two of 22 patients.” That is, the disparity would have led to different therapies, according to van Ufford and colleagues.

The authors attributed MRI’s overstaging to several factors, including variations in measurement between the techniques resulting from axial and coronal views. In addition, van Ufford and colleagues said that bone marrow metastasis may have been present in some patients, for which MRI is believed to carry greater sensitivity.

“Hence, both modalities appear to have limited sensitivity in the detection of lymphomatous bone marrow involvement,” van Ufford and co-authors wrote, therefore declaring that “bone marrow biopsy remains a crucial part of the staging workup of patients with lymphoma.”

“Our early results indicate that overall interobserver agreement at whole-body MRI-DWI is moderate to good. Overall agreement on whole-body MRI-DWI and FDG PET/CT findings is moderate,” the authors argued.

Citing their small sample size and inclusion of only newly diagnosed lymphoma patients, the authors concluded that “[u]ntil larger-scale studies show that use of whole-body MRI-DWI results in correct staging in this minority of cases, FDG PET/CT remains the reference standard for the staging of lymphoma.”