Diffusion‐weighted MRI compared to FDG PET‐CT in the staging and response assessment of Hodgkin lymphoma

Abstract

A 29-year-old man presented with a large right supraclavicular mass, weight loss and night sweats. A diagnosis of stage 4B nodular sclerosis Hodgkin lymphoma was made. F-fluorodeoxyglucose positron emission tomography with computed tomography (FDG PET-CT) and whole-body magnetic resonance imaging with diffusion-weighting (DW-MRI) were performed before and after escalated BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, prednisone) chemotherapy. The pre-treatment FDG PET-CT (top left) demonstrated extensive nodal disease above and below the diaphragm, including the right supraclavicular fossa. Post-treatment FDG PET-CT (top right) showed physiological FDG uptake only. The pre-treatment DW-MRI (bottom left) showed extensive nodal disease in the same distribution as the pre-treatment FDG PET-CT. DW-MRI revealed a bone lesion (arrow) not diagnosed on the FDG PET-CT, confirmed on the source axial images. Post-treatment morphological MRI (not shown) demonstrated residual nodal disease in the right lower neck and upper abdomen but this was all inactive on DW-MRI (bottom right). FDG PET-CT and DW-MRI independently established a complete response. FDG PET-CT is a recommended imaging method for determining disease activity in residual masses after treatment for Hodgkin lymphoma. There is an increasing body of evidence to support its use in the assessment of early response to chemotherapy and it has been established as reliable for staging Hodgkin lymphoma. However, it involves radiation exposure for both the CT and FDG components of the test. MRI does not use ionizing radiation and offers higher soft tissue contrast compared with CT. The reduction of exposure to ionizing radiation is of particular significance in patients with lymphoma who have a high chance of cure, especially in younger patients. Water diffusion whole body MRI also allows functional assessment of lymphoma response. DW-MRI relies on measuring the random motion of water molecules in tissues. Many malignant tumours, including lymphomas, are more cellular than benign/normal tissue and therefore show more restricted water diffusion, appearing bright on normal images or dark on inverted images such as those shown above. The disadvantages of MRI include the exclusion of patients with pacemakers, implantable defibrillators or significant claustrophobia. In addition, bulk tissue movements and physiological water motion can sometimes affect DW-MRI image quality. In general, FDG PET-CT is accurate for diagnosis of marrow and bone involvement in Hodgkin lymphoma but, in this case, DW-MRI revealed bone disease not diagnosed on FDG PETCT. Further research is needed to compare the relative merits of DW whole-body MRI with FDG PET-CT in the staging and monitoring of lymphoma.