Lymphoma: multifocal bone marrow involvement. Sagittal T1-weighted (500/10, TR/TE) MR image of the lumbar spine shows multiple foci of bone marrow replacement (arrows). This appearance of lymphomatous involvement of the bone marrow is similar to bone metastases. Note extraosseous mass in the presacral space with apparent preservation of the bony cortex and small retroperitoneal lymph node at the level of L2 (arrowheads).