Bone marrow reconversion mimicking pelvis metastases in a patient with rectal cancer: a pitfall on magnetic resonance images

The bone marrow is one of the largest organs in the body. There are two main types of bone marrow in human body: red and yellow bone marrow in the human body. Their proportions are determined by the overall distribution of fat and water, which ultimately determines the magnetic resonance imaging (MRI) signal intensity. At birth, red bone marrow (40% fat, 40% water and 20% protein) is present throughout the entire skeleton. It gradually converts into yellow bone marrow (80% fat, 15% water and 5% protein) (1). The conversion begins in the extremities and progresses toward the axial skeleton, and it can always be completed by approximately 25 years of age (1-3)