MR imaging of diffuse bone marrow replacement in pediatric patients with cancer.

In the magnetic resonance (MR) imaging examinations of three children with tumors (two neuroblastoma, one rhabdomyosarcoma) and three with leukemia, the marrow demonstrated a diffuse, uniform pattern of hypointensity on T1-weighted images and hyperintensity on T2-weighted images. The authors observed that this reversal ("flip-flop") of the usual MR characteristics of fatty marrow was seen in the epiphyses, metaphyses, and diaphyses. The purpose of this study was to establish the radiographic and clinicopathologic correlates of this MR finding on the basis of findings from plain radiographs, bone scans, and bone marrow aspirates. Plain radiographs and bone scans demonstrated either normal findings or changes limited to the metaphyses. In all patients, analysis of bone marrow aspirates demonstrated metastases. The authors concluded that even in the absence of evidence of discrete bone metastases on a plain radiograph or a bone scan, this diffuse and uniform "flip-flop" pattern reflects diffuse marrow replacement by tumor cells.