Leukemic infiltration - distal femur
Known case of leukemia, presented with severe knee pain.
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Well-defined areas of altered bone marrow signal intensity involving the distal femoral shaft as well as in the medial tibial plateau and the proximal fibula manifested by low signal intensity on T1 weighted images as compared to the adjacent muscles and high T2 signal intensity on the fluid sensitive fat-suppressed sequences. Soft tissue edema around the distal femur is seen. Considering the patient's history and the imaging appearance on T1, leukemic bone infiltration is highly likely.
There is mild increased signal intensity involving the body of the posterior horn of medial meniscus not extending into articular surface in keeping with mucoid degeneration. Lateral meniscus, cruciate and collateral ligaments are intact with no evidence of definite tear.
Fat component in the normal bone marrow will be replaced by leukemic cells in patients with Leukemia. The infiltration/replacement of the marrow will result in typical appearance on MRI T1 sequence where the abnormal marrow appears darker than the adjacent muscles or disks (in case of lumbar MRI studies). Additionally, the abnormal bone marrow will appear show higher signal intensity on the fluid-sensitive sequences. Leukemia can also presents as lucent metaphyseal bands classically in pediatric patients.