Evaluation of bone marrow metastasis of neuroblastoma and changes after chemotherapy by MRI

To evaluate the usefulness of MRI for diagnosing bone marrow metastasis of neuroblastoma, we compared MRI findings with histological findings. MRI was performed 26 times in 20 patients with neuroblastoma to detect metastasis to the bone marrow of the femur and tibia. Abnormal areas observed by MRI were histologically examined. The lesion visualized by MRI as a low-intensity area on T1-weighted images and as a high-intensity area on T2-weighted images was histologically confirmed to be neuroblastoma in 81% (17/21). The percentage varied according to the treatment state: 89% (8/9) by MRI imaging performed before the initiation of chemotherapy, 67% (6/9) within 3 weeks after cessation of chemotherapy (during chemotherapy), and 100% (3/3) in recurrent cases 1 year or more after chemotherapy. During the follow-up period after chemotherapy, tissue with signal intensities similar to that of bone marrow was observed in a speckled pattern in the intramedullary space on T1- and T2-weighted images. This tissue was histologically demonstrated to be normal bone marrow and was considered to be bone marrow remaining after chemotherapy. In this small series, histological findings supported the results of MRI, confirming the usefulness of MRI for diagnosing bone marrow metastasis of neuroblastoma. However, bone marrow metastasis after chemotherapy was difficult to evaluate by comparing signal intensities alone.